Progress 04/13/02 to 10/01/06
Outputs
Progress Report 1. What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? Why does it matter? Elevated ground level ozone is a major problem in many areas of the world for humans, agriculture, and natural environments. Elevated ozone- induced stress initiates premature aging in plants as well as loss of photosynthetic productivity leading to substantial losses in vegetative, fruit and/or grain yield, resulting in substantial economic losses for sites all over the world. Also, global warming, apparently caused by rising atmospheric carbon dioxide levels, is another problem for the United States' and the world's agriculture. Warming of the earth is believed to contribute to the increasing frequency of drought-induced water stress of crops, resulting in tremendous losses in agricultural productivity and threatening the world food supply. Understanding the various physiological
and biochemical aspects of tolerance mechanisms of crop plants to ozone-induced and drought-induced water stress is important for selecting the most appropriate cultivar and management practices. Thus, more basic information is urgently needed that will assist plant breeders in developing elevated ozone-tolerant and/or drought-tolerant cultivars of all crops. This research directly contributes to the accomplishment of ARS National Program 203 (Air Quality). 2. List by year the currently approved milestones (indicators of research progress) Year 1 (FY 2002) Develop and validate techniques to extract and measure antioxidants and pyridine cofactors from both symplastic and apoplastic extracts. Examine and quantitate antioxidant levels and their redox status as a result of oxidative stress in soybean cultivars. Year 2 (FY 2003) Finish development and validation of techniques to extract and measure antioxidants and pyridine cofactors from both symplastic and apoplastic extracts. Develop
extraction and measuring techniques for ribulose-1,5- bisphosphate carboxylase/oxygenase, glyceraldehyde 3P dehydrogenase, and fructose bisphosphate. Continue to examine and to quantitate antioxidant levels and their redox status as a result of ozone induced oxidative stress in soybean cultivars. Examine the influence of elevated CO2 exposure on the relationship between the photosynthetic carbon metabolism, photosynthate partitioning and the synthesis of ascorbic acid in the leaves of barley. Year 3 (FY 2004) Continue examining the influence of elevated CO2 exposure on the relationship between the photosynthetic carbon metabolism, photosynthate partitioning and the synthesis of ascorbic acid in the leaves of barley and wheat. Year 4 (FY 2005) Examine the enzymes of ascorbate synthesis pathway in leaves of sunflower infected with the organism Pseudomonas syringae pv tagetin to determine how tagetitoxin causes a reduction in foliar levels of ascorbate in infected leaves. Determine how
hexose phosphate metabolism and partitioning to ascorbate has been affected by tagetitoxin. Examine the relationship between sunflower leaf ascorbate concentration, and gene expression in sunflower plants that are associated with the attempted defense against tagetitoxin attacks on chloroplast RNA synthesis enzymes, e.g. RNA polymerase. Year 5 (FY 2006) Examine foliar ascorbic acid relations in relationship to photosynthesis during ozone exposure and during drought in spinach and soybean. 4a List the single most significant research accomplishment during FY 2006. "Drought increases the oxygen inhibition of photosynthesis in soybean." Work in the Crop Systems and Global Change Laboratory determined that the oxygen inhibition of photosynthesis in soybeans under water stress was not predictable from the oxygenation function of the ribulose bisphosphate carboxylase/oxygenase enzyme, because it increased under stress and was no longer reversible by high carbon dioxide concentrations. This
indicates that oxygen has a previously unknown role in affecting photosynthesis during drought. This work will be of interest to scientists trying to increase the drought tolerance of crops. NP 203, Component IV. The scientist position has been vacant since 01/01/2006. The project will terminate on 09/30/2006. 4b List other significant research accomplishment(s), if any. Contributed to a multi-location comparison of two snap bean cultivars for the sensitivity of yield to ozone by relating yield differences to ozone levels in different locations and times during the season. NP 203, Component IV. 5. Describe the major accomplishments to date and their predicted or actual impact. Demonstrated that there was a correlation between ozone tolerance in soybean cultivar Essex and higher levels of ascorbic acid (ASC) in leaves when compared with ozone sensitive soybean cv Forrest. Higher ASC levels in cv Essex accompanied a greater ozone tolerance of leaf photosynthesis and stomatal
conductance compared with cv Forrest. These studies suggested that, relative to ozone-sensitive cv Forrest, leaf cells of ozone-tolerant cv Essex may have more active enzymes which regenerate ASC. Further, we observed higher activities of compounds which are able to remove damaging peroxides and superoxides, than are leaf cells of cv Forrest. An additional important accomplishment has been the recognition that an economically important plant pathogen, P. syringae pv tagetin during infection of sunflower plants, causes an apparent inhibition of the synthesis of ascorbic acid as well as dark respiration in the leaves. There is also a concurrent severe inhibition of photosynthesis accompanied by an inhibition of starch and sucrose synthesis. Thus, the influence of P. syringae pv tagetin infection on sunflower leaf photosynthesis, photosynthate partitioning, as well as apparent dark respiration, provides an important tool to examine the relationship between chloroplast photosynthesis,
photosynthate partitioning, and respiration with respect to ascorbic acid synthesis. Work on this project provided the first direct evidence in soybean leaves for the galactose pathway for ascorbic acid synthesis and that this pathway is inhibited by exposure to ozone. Thus chronic ozone stress results in loss of the active form of ascorbic acid which also results in a severe loss of photosynthetic productivity. In collaboration with the College Miseracordia, Dallas, Pennsylvania evidence was found that there are compounds in soybean leaf in cell walls. These compounds act as signals to cause an increase in activities of antioxidant enzymes systems that help the leaves to tolerate exposure to elevated atmospheric ozone levels. NP 203, Component IV. 6. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the
adoption and durability of the technology products? Methods were developed in USDA-ARS Beltsville for the extraction and measurement of foliar ascorbic acid components, as well as methods for the in vivo analyses of enzymes associated with the synthesis of ascorbic acid in crop plant leaves. These methods are being employed by USDA-ARS plant physiolgists at Raleigh, North Carolina, and by USDA, ARS plant physiologists at Champaign-Urbana, Illinois.
Impacts
(N/A)
Publications
- Robinson, J.M., Sicher Jr, R.C. 2004. Antioxidant levels decline in primary leaves of barley during growth at ambient and elevated carbon dioxide levels. International Journal of Plant Science. 165(6):965-972.
|
Progress 10/01/04 to 09/30/05
Outputs
1. What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? What does it matter? Elevated tropospheric ozone level is a major problem in many areas of the world for humans, agriculture, and natural environments. Elevated ozone- induced stress initiates premature aging in plants as well as loss of photosynthetic productivity leading to substantial losses in vegetative, fruit and/or grain yield, resulting in substantial economic losses for sites all over the world. Also, global warming, apparently caused by rising atmospheric carbon dioxide levels, is another problem for the United States' and the world's agriculture. Warming of the earth is believed to contribute to the increasing frequency of drought-induced water stress of crops, resulting in tremendous losses in agricultural productivity and threatening the world food supply. Understanding the various physiological and
biochemical aspects of tolerance mechanisms of crop plants to ozone-induced and drought-induced water stress is important for selecting the most appropriate cultivar and management practices. Thus, more basic information is urgently needed that will assist plant breeders in developing elevated ozone-tolerant and/or drought-tolerant cultivars of all crops. Studies by USDA, ARS, Crop Systems and Global Change Laboratory (CSGCL) scientists at Beltsville have revealed the ability of crop plant leaf cells to maintain the antioxidant ascorbic acid (vitamin C) in the active state as a factor that assists some soybean cultivars to withstand, and to yield, normally during prolonged exposure to elevated ozone and drought-induced water stress. As a result, the ongoing and previous research in the CSGCL, studies are now going forward to examine: 1) the influence of prolonged elevated ozone-induced stress on leaf components responsible for ascorbic acid (Vitamin C) synthesis; 2) the influence of
drought-induced water stress on leaf components associated with maintaining leaf ascorbic acid (Vitamin C) in the active state and leaf components responsible for the synthesis of ascorbic acid; and 3) the affect of ozone-induced stress and drought-induced water stress on foliar photosynthate partitioning to support the synthesis of ascorbic acid. This research supports National Program 203: Air Quality (60%), Component IV - Ozone Impacts and National Program 204: Global Climate Change (40%), Component III - Agricultural Ecosystems Impacts. 2. List the milestones (indicators of progress) from your Project Plan. FY 2002 Develop and validate techniques to extract and measure antioxidants and pyridine cofactors from both symplastic and apoplastic extracts. Examine and quantitate antioxidant levels and their redox status as a result of oxidative stress in soybean cultivars. FY 2003 Finish development and validation of techniques to extract and measure antioxidants and pyridine cofactors
from both symplastic and apoplastic extracts. Develop extraction and measuring techniques for ribulose-1,5- bisphosphate carboxylase/oxygenase, glyceraldehyde 3P dehydrogenase, and fructose bisphosphate. Continue to examine and to quantitate antioxidant levels and their redox status as a result of ozone induced oxidative stress in soybean cultivars. Examine the influence of elevated CO2 exposure on the relationship between the photosynthetic carbon metabolism, photosynthate partitioning and the synthesis of ascorbic acid in the leaves of barley. FY 2004 Continued examining the influence of elevated CO2 exposure on the relationship between the photosynthetic carbon metabolism, photosynthate partitioning and the synthesis of ascorbic acid in the leaves of barley and wheat. Barley plant treatments were conducted in high light growth chambers equipped with a system to permit manipulating the growth chamber CO2 levels. Examined the influence of elevated ozone on the relationship between
photosynthetic carbon metabolism and photosynthate partitioning to support ascorbic acid synthesis. This work was conducted in the leaves of a mutant of Arabidopsis thallania which has been genetically manipulated to have a deficiency in the carbon assimilatory pathway associated with ascorbate synthesis and has low ascorbate. Other Arabidopsis mutants were employed that had deficiencies in photosynthetic carbon assimilatory capacity. 3a List the milestones that were scheduled to be addressed in FY 2005. For each milestone, indicate the status: fully met, substantially met, or not met. If not met, why. 1. Examine the enzymes of ascorbate synthesis pathway in leaves of sunflower infected with the organism Pseudomonas syringae pv tagetin to determine how tagetitoxin causes a reduction in foliar levels of ascorbate in infected leaves. Milestone Not Met Other 2. Determine how hexose phosphate metabolism and partitioning to ascorbate has been affected by tagetitoxin. Milestone Not Met
Other 3. Examine the relationship between sunflower leaf ascorbate concentration, and gene expression in sunflower plants that are associated with the attempted defense against tagetitoxin attacks on chloroplast RNA synthesis enzymes, e.g. RNA polymerase. Milestone Not Met Other 3b List the milestones that you expect to address over the next 3 years (FY 2006, 2007, and 2008). What do you expect to accomplish, year by year, over the next 3 years under each milestone? FY 2006 1) Experiments-O3: Two experiments on foliar ascorbic acid relations will be conducted in the greenhouse open top chambers in the early to mid spring and two experiments in the late spring with one spinach cultivar. Two experiments on abscorbic acid relations in the greenhouse open top chambers with soybean cultivars in the early to mid summer. One experiment conducted with snapbean at the field site from May through August (vegetative stages and leaf ages). 2) Experiments Drought: Two experiments on ascorbic
acid relations with soybean and spinach cultivars in the growth chambers and the greenhouse. 4a What was the single most significant accomplishment this past year? This phase of the research began to study whether exposure of soybean cultivars to elevated ozone inhibits enzymes in the foliar ASC synthesis pathway. Addition of exogenous L-galactose (GAL) and/or L-galactono-1,4- lactone (GL) through the petietiols of leaflets of the soybean cultivars Essex and cv Forrest, ultimately tripled the amount of endogenous foliar L-ascorbic acid during incubation periods of one hour in high light. Leaflets from cv Essex and cv Forrest growing in very low O3 levels rapidly converted these metabolites to ASC. This is consistent with the currently proposed enzymatic pathway for conversion of GAL to GL catalyzed by the enzyme GAL dehydrogenase, and the conversion of GL directly to ASC catalyzed by the enzyme, GL dehydrogenase. This is the first direct evidence in soybean leaves for the
galactose pathway for ascorbic synthesis. Additionally, in cv Essex and cv Forrest plants exposed to elevated ozone for 40 days, GAL and/or GL dependent ASC synthesis in leaflets were significantly decreased relative to the leaflets of these cultivars in carbon filtered air (low ozone). It is now hypothesized that the enzymes L-galactose dehydrogenase and L-galactono-1,4-lactone dehydrogenase, the terminal enzymes in the ASC synthesis pathway, are sensitive to ROS resulting from prolonged elevated O3 exposure. Since all intermediates in the ASC synthesis pathway were not examined in this study, it is not clear whether the activities of all enzymes in the pathway were negatively influenced by O3. However, it is very likely that the degradation of many foliar proteins during prolonged O3 exposure induced senescence will include those associated with the ascorbic acid synthesis pathway, involved in vital metabolic pathways. Thus chronic elevated ozone stress could result in loss in
the active form of Vitamin C which would, and does result in a severe loss of photosynthetic productivity. 4b List other significant accomplishments, if any. In collaboration with Dr. Cosima B. Weise, College Miseracordia, Dallas, Pennsylvania: Found evidence that there are compounds in soybean leaf in cell walls that act as signals to cause an increase in activities of antioxidant enzymes systems that help the leaves to tolerate exposure to elevated atmospheric ozone levels. 5. Describe the major accomplishments over the life of the project, including their predicted or actual impact. Demonstrated that there was a correlation between ozone tolerance in soybean cultivar Essex and higher foliar levels of the antioxidant ascorbic acid (ASC) as well as a higher ascorbate to dehydroascorbate (its oxidation product) redox status when compared with O3-sensitive soybean cv Forrest. Higher ASC redox status in cv Essex accompanied a greater O3-tolerance of leaf photosynthesis and stomatal
conductance compared with cv Forrest. These studies suggested that, relative to O3- sensitive cv Forrest, leaf cells of O3-tolerant cv Essex may have more active enzymes of the ascorbate-glutathione cycle, for example, glutathione reductase. This would facilitate a more rapid DHA to ASC recycling which would support maintenance of as much as 99% of the total ascorbic acid in its reduced form, and allow the cells to meet the demands for ASC to remove H2O2. Further, we observed higher activities of cytosolic ascorbate peroxidases and superoxide dismutases in O3- tolerant cv Essex, compared with O3-sensitive cv Forrest. This suggests that during O3 exposure, leaf cells of cv Essex are able to more rapidly remove H2O2 and O2, than are leaf cells of cv Forrest. An additional important accomplishment has been the recognition that an economically important plant pathogen, P. syringae pv tagetin during infection of sunflower plants, causes an apparent inhibiton of the synthesis of
ascorbic acid as well as a concurrent dark respiration in the leaves. There is also a concurrent severe inhibition of photosynthesis accompanied by an inhibition of starch and sucrose synthesis. Thus, the influence of P. syringae pv tagetin infection on sunflower leaf photosynthesis, photosynthate partitioning, as well as apparent dark or mitochondrial respiration provides an important tool to examine the relationship between chloroplast photosynthesis, photosynthate partitioning and mitochondrial respiration with respect to ascorbic acid synthesis. 6. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? Technology transfer is associated with the use of methods, developed in USDA,ARS Beltsville, for extraction and measurement of foliar ascorbic acid
components and methods for the in vivo analyses of enzymes associated the synthesis of ascorbic acid in crop plant leaves. This methodology and publications employing these methodologies are being employed USDA-ARS plant physiologists at Raleigh, North Carolina, and by USDA, ARS Plant Physiolgists at Champaign-Urbana, Illinois. 7. List your most important publications in the popular press and presentations to organizations and articles written about your work. (NOTE: List your peer reviewed publications below). Robinson J. M. 2005 Does prolonged exposure of soybean plants to elevated ozone cause inhibition and/or inactivation of the foliar ascorbic acid synthesis pathway enzymes, galactose dehydrogenase and galactono-1,4- dehydrogenase and galactono-1,4-dehydroagenase? Plant Biology 2005, Final Program (Poster Presentation at the 2005 National Meeting of the American Society of Plant Biologists, Seattle, Washington USA, July 16- July 20, 2005) (Abstract): Poster #112: page 118.
(Log #179230).
Impacts
(N/A)
Publications
- Robinson, J.M., Sicher Jr, R.C. 2004. Antioxidant levels decline in primary leaves of barley during growth at ambient and elevated carbon dioxide levels. International Journal of Plant Science. 165(6):965-972.
|
Progress 10/01/03 to 09/30/04
Outputs
1. What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? What does it matter? Ozone (O3), a naturally occurring component of earth's atmosphere, is steadily rising in areas of the earth's troposphere due to human domestic and industrial activities. Unfortunately, tropospheric O3 is rising to very high levels in many North American agricultural areas. In the spring and summer growing seasons, levels of O3 often rise to as high as 40 to 150 nL L-1, and at these higher levels, O3 is phytotoxic. Ozone can cause damage to leaves of ornamental, horticultural, and agronomic crops. It penetrates into the leaves through the stomata, into intracellular air spaces, and then into cell walls where it decomposes to highly-toxic, oxygen-containing molecules, such as superoxide radical, hydroxyl radical, peroxyradical, and hydrogen peroxide. These reactive oxygen molecules can damage plant
cell membranes and photosynthetic mechanisms, ultimately resulting in reduced vegetable, grain, and fruit yields. Global warming, apparently caused by rising atmospheric CO2 levels, is another potential problem for the United States' and the world's agriculture. Warming of the earth is believed to contribute to the increasing frequency of drought-induced water stress of crops, resulting in tremendous losses in agricultural productivity and threatening the world food supply. Drought induced-water stress of crop plants results in inhibition of photosynthesis by reactive oxygen molecules in the plant leaf cells which, in turn, leads to oxidative stress. The crop losses due to ozone-induced oxidative stress are estimated to be in the millions of dollars for North American agriculture alone. Additionally, the recent increase in the duration of drought in parts of North America has caused considerable crop loss. For example, over the last four years, in some Midwestern states such as
Kansas and eastern Colorado, drought has caused as much as a 30% decrease or more in yield in grass crops such as hard red winter wheat. Understanding the various physiological aspects of tolerance of crop plants to ozone-induced and drought-induced water stress is important for selecting the most appropriate cultivar and management practices. Based upon recent environmental emergencies, more basic information which will assist plant breeders in developing O3-tolerant and/or drought-tolerant cultivars of crops is urgently needed. ARS-Environmental Quality Laboratory scientists have shown the ability of leaf cells to maintain the antioxidant ascorbic acid (vitamin C) in the reduced (or active) state as a factor that assists soybean cultivars to be ozone tolerant and to yield normally during season-long exposure to elevated ozone. We also have observed that during drought-induced water stress, the leaves of some cultivars of soybean and spinach maintain ascorbic acid in the reduced
form, thus presumably assisting the plant leaf cells to cope with oxidative stress caused by the internally generated toxic oxygen molecules. A major objective of this project is to determine the role of the oxidation-reduction turnover and synthesis of ascorbic acid (ASC) in relation to crop plant tolerance to oxidative stress, resulting from prolonged exposure to elevated tropospheric O3 and to drought-induced water stress. Differences in ascorbic acid oxidation-reduction and synthesis processes will be identified in various cultivars that could be genetically manipulated to improve crop plant tolerance to O3-induced and drought stress induced oxidative stress. Our research will be conducted in the greenhouse, in the field, as well as in the laboratory. The information produced in these studies will be important to plant geneticists and to breeders developing crop cultivars tolerant of oxidative stress caused by elevated tropospheric ozone and/or drought- induced water stress.
This information will benefit crop breeders, geneticists, farmers, agribusinesses, consumers, and environmental lawmakers and policymakers. This research supports National Program 203: Air Quality (60%), Component IV - Ozone Impacts and National Program 204: Global Climate Change (40%), Component III - Agricultural Ecosystems Impacts. 2. List the milestones (indicators of progress) from your Project Plan. FY 2002 Develop and validate techniques to extract and measure antioxidants and pyridine cofactors from both symplastic and apoplastic extracts. Examine and quantitate antioxidant levels and their redox status as a result of oxidative stress in soybean cultivars. FY 2003 Finish development and validation of techniques to extract and measure antioxidants and pyridine cofactors from both symplastic and apoplastic extracts. Develop extraction and measuring techniques for ribulose-1,5- bisphosphate carboxylase/oxygenase, glyceraldehyde 3P dehydrogenase, and fructose bisphosphate.
Continue to examine and to quantitate antioxidant levels and their redox status as a result of oxidative stress in soybean cultivars. Examine the influence of elevated CO2 exposure on the relationship between the photosynthetic carbon metabolism, photosynthate partitioning and the synthesis of ascorbic acid in the leaves of barley and wheat. FY 2004 Continue to examine the influence of elevated CO2 exposure on the relationship between the photosynthetic carbon metabolism, photosynthate partitioning and the synthesis of ascorbic acid in the leaves of barley and wheat. Barley plant treatments will be conducted in high light growth chambers equipped with a system to permit manipulating the growth chamber CO2 levels. Examine the influence of elevated ozone on the relationship between photosynthetic carbon metabolism and photosynthate partitioning to support ascorbic acid synthesis. This work will be conducted in the leaves of a mutant of Arabidopsis thallania which has been genetically
manipulated to have a deficiency in the carbon assimilatory pathway associated with ascorbate synthesis and has low ascorbate. Other Arabidopsis mutants will be employed that have deficiencies in photosynthetic carbon assimilatory capacity. FY 2005 Examine the enzymes of ascorbate synthesis pathway in leaves of sunflower infected with the organism Pseudomonas syringae pv tagetin to determine how tagetitoxin causes a reduction in foliar levels of ascorbate in infected leaves. Determine how hexose phosphate metabolism and partitioning to ascorbate has been affected by tagetitoxin. Examine the relationship between sunflower leaf ascorbate concentration, and gene expression in sunflower plants that are associated with the attempted defense against tagetitoxin attacks on chloroplast RNA synthesis enzymes, e.g. RNA polymerase. FY 2006 Develop techniques for the extraction and quantitation of soybean leaf lipid hydroperoxides and lipid hydroperoxide breakdown products such as malondialdehyde
to use as markers for assessing ozone-induced and drought- induced oxidative stress in soybean leaves. Use soybean plants exposed to elevated ozone and/or drought stress in the green house and in the field to define the extent of oxidative stress caused by ozone and/or drought. Develop techniques for extraction and measurement of protein sulfhydryl status and assess the protein sulfhydryl status to use as markers for oxidative stress in leaves of soybean plants exposed to elevated ozone or drought in the greenhouse and in the field. Develop methods for extraction and quantitation of enzymes of the ascorbate-glutathione cycle as well as the enzymes of the photosynthetic pentose phosphate reductive cycle and enzymes of the oxidative pentose cycle in soybean cultivars. Measure the impact of drought-and/or ozone-induced oxidative stress on these enzyme systems and attempt to correlate protein sulfhydryl status with enzyme inhibitions caused by oxidative stress associated with elevated
ozone and/or drought. Prepare new project prospectus and plan. FY 2007 Continue to examine the impact of drought-and/or ozone-induced oxidative stress on enzyme systems and attempt to correlate protein sulfhydryl status with enzyme inhibitions caused by oxidative stress associated with elevated ozone and/or drought. Complete preparation of new project plan. 3. Milestones: 3A. The milestones listed below were scheduled to be addressed in FY 2004: Continue to examine the influence of elevated CO2 exposure on the relationship between the photosynthetic carbon metabolism, photosynthate partitioning, and the synthesis of ascorbic acid in the leaves of barley and wheat. SUBSTANTIALLY MET. Barley plant treatments will be conducted in high light growth chambers equipped with a system to permit manipulating the growth chamber CO2 levels. SUBSTANTIALLY MET. Examine the influence of elevated ozone on the relationship between photosynthetic carbon metabolism and photosynthate partitioning to
support ascorbic acid synthesis. This work will be conducted in the leaves of a mutant of Arabidopsis thallania which has been genetically manipulated to have a deficiency in the carbon assimilatory pathway associated with ascorbate synthesis and has low ascorbate. PARTIALLY MET. No new studies were conducted after January 2004. Other Arabidopsis mutants will be employed that have deficiencies in photosynthetic carbon assimilatory capacity. NOT MET. This work was not conducted. 3B. The milestones listed below are expected to be addressed over the next 3 years: FY 2005 Examine the enzymes of ascorbate synthesis pathway in leaves of sunflower infected with the organism Pseudomonas syringae pv tagetin to determine how tagetitoxin causes a reduction in foliar levels of ascorbate in infected leaves. Determine how hexose phosphate metabolism and partitioning to ascorbate has been affected by tagetitoxin. Examine the relationship between sunflower leaf ascorbate concentration, and gene
expression in sunflower plants that are associated with the attempted defense against tagetitoxin attacks on chloroplast RNA synthesis enzymes, e.g. RNA polymerase. Much of this work will be conducted in collaboration with ARS-Sustainable Agricultural Systems Laboratory (J. Lydon), Beltsville, Maryland. FY 2006 Develop techniques for the extraction and quantitation of soybean leaf lipid hydroperoxides and lipid hydroperoxide breakdown products such as malondialdehyde to use as markers for assessing ozone-induced and drought- induced oxidative stress in soybean leaves. Use soybean plants exposed to elevated ozone and/or drought stress in the green house and in the field to define the extent of oxidative stress caused by ozone and/or drought. This work will be conducted in collaboration with ARS-Alternate Crops Systems Laboratory (J. Bunce), Beltsville, Maryland. Develop techniques for extraction and measurement of protein sulfhydryl status and assess the protein sulfhydryl status to
use as markers for oxidative stress in leaves of soybean plants exposed to elevated ozone or drought in the greenhouse and in the field. Develop methods for extraction and quantitation of enzymes of the ascorbate-glutathione cycle as well as the enzymes of the photosynthetic pentose phosphate reductive cycle and enzymes of the oxidative pentose cycle in soybean cultivars. Measure the impact of drought-and/or ozone-induced oxidative stress on these enzyme systems and attempt to correlate protein sulfhydryl status with enzyme inhibitions caused by oxidative stress associated with elevated ozone and/or drought. This work will be conducted using soybean plants grown in the greenhouse and/or a field crop environment. Prepare new project prospectus and plan. FY 2007 Continue to examine the impact of drought-and/or ozone-induced oxidative stress on enzyme systems and attempt to correlate protein sulfhydryl status with enzyme inhibitions caused by oxidative stress associated with elevated
ozone and/or drought. Complete preparation of new project plan. 4. What were the most significant accomplishments this past year? 4A. Single most significant accomplishment during FY 2004: It is now well established that a major problem in agricultural areas, especially those adjacent to industrial areas, is that elevated tropospheric ozone levels are phytotoxic to many crop plant species, e.g. winter wheat, soybean, potatoes, etc., with significant losses in yield. Research is ongoing to understand the mechanisms by which the ascorbic acid (an antioxidant) assists the cells and tissues of plant leaves and other organs to tolerate ozone and drought stress, but due to space retraints in plant growth systems, e.g., greenhouses and growth chambers, new techniques are required that use fewer number of crop plant cultivars and at the same time maintain correctly designed experiments that are statistically valid. In a study examining the physiology of soybean leaflets, each of the three
leaflets of the newly, fully expanded, and/or mature leaves of soybean cultivars were found to be statistically the same in ascorbic acid relations (levels and redox status), net photosynthesis rates, stomatal conductance, and transpiration rates. These results are important to other plant physiologists whose mission is to understand the mechanism of tolerance to ozone-induced stress in other soybean cultivars and other legumes with three leaflets per leaf at each node. 4B-D. None. 5. Describe the major accomplishments over the life of the project, including their predicted or actual impact. The soybean cultivar (cv) Essex has been shown to be tolerant and cv Forrest to be sensitive to the high ozone levels frequently observed in many North American agricultural areas. Studies were conducted to examine the relationship of soybean leaf ascorbate redox and the foliar photosynthesis. The ascorbate-dehydroascorate redox status as well as photosynthesis in cv Essex were always higher in
the mature leaflets of cv Essex than in those of cv Forrest, indicating that greater tolerance to ozone is directly related to ascorbate's role in protecting enzymes of photosynthetic carbon assimilation. This study provides stronger evidence indicating that soybean breeders and genetic engineers, whose mission is to develop elevated ozone tolerant soybeans, should be attempting to increase foliar ascorbic acid levels and the activities of enzymes that help maintain ascorbic acid in the reduced form. Exposure of several grass crops, such as wheat and barley, to elevated carbon dioxide (CO2) levels often induces senescence and/or oxidative stress in the leaves. In a collaborative project with ARS-Alternate Crops and Systems Laboratory, experiments were conducted to determine how the primary leaves of elevated CO2 exposed barley plants were attempting to manage the oxidative stress. Concurrent with a dramatic drop in photosynthesis and photosynthetic carbohydrate production (leaf
senescence), a pronounced decline in the antioxidants, ascorbic acid and glutathione, was observed in the primary leaves of barley plants exposed to elevated CO2 level. Results of this study are important to plant physiologists; to environmentalists; and to human, animal and plant nutritionists because elevated CO2 level is identified as a phytotoxic air pollutant that is related to leaf senescence causing a concurrent decline in levels of antioxidants such as ascorbate and glutathione. The soybean cultivar (cv) Essex has been shown to be tolerant and cv Forrest sensitive to the high ozone levels frequently observed in many North American agricultural areas. The role of cell wall phenolic compounds in the differential sensitivity of two soybean cultivars to ozone was investigated. Data indicted a quantitative difference between ozone tolerant cultivar cv Essex and ozone sensitive cultivar cv Forrest in certain phenolic compounds of the foliar cell wall. These results suggest that
phenolic compounds may play a role in the antioxidant capacity of the leaf cells and the variation in the oxidative tolerance of soybean cultivars. The roles of leaf cell chloroplast and leaf cell mitochondria in the maintenance of ascorbic acid levels were examined. Studies were conducted, in collaboration with ARS-Sustainable Agricultural Systems Laboratory, to measure the antioxidant ascorbic acid and its redox components in the leaves of sunflower plants infected with the bacteria Pseudomonas syringae pv tagetin which produces tagetitoxin, a coupound that causes abnormal chloroplast development and appears to inhibit the mitochondrial function in the leaf cell. The results implied that the carbohydrate products of photosynthetic carbon dioxide assimilation, such as glucose, and one or more functions of mitochondrial respiration, are concurrently required for the maintenance of normal levels of ascorbic acid (vitamin C) in green leaves. The results further suggest that normal
ascorbate synthesis and maintenance of ascorbic acid level in plant leaf cells requires ongoing normal photosynthesis and mitochondrial respiratory function. Soybean breeders and genetic engineers, whose mission it is to develop elevated ozone tolerant soybeans, need to know what traits will affect a cultivar to be more tolerant to oxidative stress. Results thus far indicate that increased foliar ascorbic acid levels and enzymes that assist in maintaining ascorbic acid in the reduced form are highly desirable as well as cultivars that exhibit a cooperation between leaf cell chloroplasts and mitochondria in the synthesis and maintenance of ascorbic acid in leaf cells. This also suggests that any genetic improvement on increasing levels of ascorbic acid in leaves is going to be more complicated than just increasing the activities of rate-limiting enzymes of the ascorbic acid synthesis pathway. Understanding the various physiological aspects of tolerance of crop plants to ozone-
induced stress is important for selecting the most appropriate cultivar and management practices. 6. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? The information produced in these studies will be important to plant geneticists and to breeders developing crop cultivars tolerant of oxidative stress caused by elevated tropospheric ozone and/or drought- induced water stress. This information will benefit crop breeders, geneticists, farmers, agribusinesses, consumers, and environmental lawmakers and policymakers.
Impacts
(N/A)
Publications
- Robinson, J.M., Lydon, J., Murphy, C.A., Rowland, R., Smith, R. 2004. Effect of pseudomonas syringae pv. tagetis infection on sunflower leaf photosynthesis and ascorbic acid relations. International Journal of Plant Science. 165:263-271.
|
Progress 10/01/02 to 09/30/03
Outputs
1. What major problem or issue is being resolved and how are you resolving it? Ozone (O3), a naturally occurring component of earth's atmosphere, is steadily rising in areas of the earth's troposphere due to human domestic and industrial activities. Unfortunately, tropospheric O3 is rising to very high levels in many North American agricultural areas. In the Spring and Summer growing seasons, levels of O3 often rise to as high as 40 to 150 nL L-1, and at these higher levels, O3 is phytotoxic. Ozone can cause damage to leaves of ornamental, horticultural, and agronomic crops. It penetrates into the leaves through the stomata, into intracellular air spaces, and then into cell walls where it decomposes to highly-toxic, oxygen-containing molecules, such as superoxide radical, hydroxyl radical, peroxyradical, and hydrogen peroxide. These reactive oxygen molecules can damage plant cell membranes and photosynthetic mechanisms ultimately resulting in reduced vegetable,
grain, and fruit yields. Global warming, apparently caused by rising atmospheric CO2 levels, is another potential problem for U.S. and the world's agriculture. Warming of the earth is believed to contribute to the increasing frequency of drought-induced water stress of crops, resulting in tremendous losses in agricultural productivity and threatening the world food supply. Drought induced-water stress of crop plants results in inhibition of photosynthesis by reactive oxygen molecules in the plant leaf cells which, in turn, leads to oxidative stress. ARS-Environmental Quality Laboratory scientists have shown the ability of leaf cells to maintain the antioxidant ascorbic acid (vitamin C) in the reduced (or active) state as a factor that assists soybean cultivars to be ozone tolerant and yield normally during season-long exposure to elevated ozone. We also have observed that during drought-induced water stress, the leaves of some cultivars of soybean and spinach are to maintain
ascorbic acid in the reduced form, thus presumably assisting the plant leaf cells to cope with oxidative stress caused by the internally generated toxic oxygen molecules. A major objective of this project is to determine the role of the oxidation-reduction turnover and synthesis of ascorbic acid (ASC) in relation to crop plant tolerance to oxidative stress, resulting from prolonged exposure to elevated tropospheric O3 and to drought-induced water stress. Differences in ascorbic acid oxidation-reduction and synthesis processes will be identified in various cultivars that could be genetically manipulated to improve crop plant tolerance to O3-induced and drought stress induced oxidative stress. Our research will be conducted in the greenhouse, in the field, as well as in the laboratory. The information produced in these studies will be important to plant geneticists and to breeders developing crop cultivars tolerant of oxidative stress caused by elevated tropospheric ozone and/or
drought- induced water stress. This information will benefit crop breeders, geneticists, farmers, agribusinesses, consumers, and environmental lawmakers and policymakers. 2. How serious is the problem? Why does it matter? The crop losses due to ozone-induced oxidative stress are estimated to be in the millions of dollars to North American agriculture alone. Additionally, the recent increase in the duration of drought in parts of North America has caused considerable crop loss. For example, over the last four years, in some Midwestern states such as Kansas and eastern Colorado, drought has caused as much as a 30% decrease or more in yield in grass crops such as hard red winter wheat. Understanding the various physiological aspects of tolerance of crop plants to ozone-induced and drought-induced water stress is important for selecting the most appropriate cultivar and management practices. Based upon recent environmental emergencies, more basic information which will assist plant
breeders in developing O3-tolerant and/or drought-tolerant cultivars of crops is urgently needed. 3. How does it relate to the National Program(s) and National Program Component(s) to which it has been assigned? This research supports National Program 203: Air Quality (60%), Component IV - Ozone Impacts and National Program 204: Global Climate Change (40%), Component III - Agricultural Ecosystems Impacts. 4. What were the most significant accomplishments this past year? A. Single most significant accomplishment during FY2003: The soybean cultivar (cv) Essex has been shown to be tolerant and cv Forrest sensitive to the high ozone levels frequently observed in many North American agricultural areas. Studies were conducted to examine the relationship of soybean leaf ascorbate redox and the foliar photosynthesis. The ascorbate-dehydroascorate redox status as well as photosynthesis in cv Essex were always higher in the mature leaflets of cv Essex than in those of cv Forrest, indicating
that greater tolerance to ozone is directly related to ascorbate's role in protecting enzymes of photosynthetic carbon assimilation. This study provides stronger evidence indicating that soybean breeders and genetic engineers, whose mission is to develop elevated ozone tolerant soybeans, should be attempting to increase foliar ascorbic acid levels and the activities of enzymes that help maintain ascorbic acid in the reduced form. B. Other significant accomplishments. Exposure of several grass crops, such as wheat and barley, to elevated carbon dioxide (CO2) levels often induces senescence and/or oxidative stress in the leaves. In a collaborative project with ARS-Alternate Crops and Systems Laboratory, experiments were conducted to determine how the primary leaves of elevated CO2 exposed barley plants were attempting to manage the oxidative stress. Concurrent with a dramatic drop in photosynthesis and photosynthetic carbohydrate production (leaf senescence), a pronounced decline in
the antioxidants, ascorbic acid and glutathione, was observed in the primary leaves of barley plants exposed to elevated CO2 level. Results in this study are important to plant physiologists; to environmentalists; and to human, animal and plant nutritionists because elevated CO2 level is identified as a phytotoxic air pollutant that is related to leaf senescence causing a concurrent decline in levels of antioxidants such as ascorbate and glutathione. The soybean cultivar (cv) Essex has been shown to be tolerant and cv Forrest sensitive to the high ozone levels frequently observed in many North American agricultural areas. The role of cell wall phenolic compounds in the differential sensitivity of two soybean cultivars to ozone was investigated. Data indicted a quantitative difference between ozone tolerant cultivar cv Essex and ozone sensitive cultivar cv Forrest in certain phenolic compounds of the foliar cell wall. These results suggest that phenolic compounds may play a role in
the antioxidant capacity of the leaf cells and the variation in the oxidative tolerance of soybean cultivars. The roles of leaf cell chloroplast and leaf cell mitochondria in the maintenance of ascorbic acid levels were examined. Studies were conducted, in collaboration with ARS-Sustainable Agricultural Systems Laboratory, to measure the antioxidant ascorbic acid and its redox components in the leaves of sunflower plants infected with the bacteria Pseudomonas syringae pv tagetin which produces tagetitoxin, a coupound that causes abnormal chloroplast development and appears to inhibit the mitochondrial function in the leaf cell. The results implied that the carbohydrate products of photosynthetic carbon dioxide assimilation, such as glucose, and one or more functions of mitochondrial respiration, are concurrently required for the maintenance of normal levels of ascorbic acid (vitamin C) in green leaves. The results further suggest that normal ascorbate synthesis and maintenance of
ascorbic acid level in plant leaf cells requires ongoing normal photosynthesis and mitochondrial respiratory function. C-D. None 5. Describe the major accomplishments over the life of the project, including their predicted or actual impact. Soybean breeders and genetic engineers, whose mission it is to develop elevated ozone tolerant soybeans, need to know what traits will affect a cultivar to be more tolerant to oxidative stress. Results thus far indicate that increased foliar ascorbic acid levels and enzymes that assist in maintaining ascorbic acid in the reduced form are highly desirable as well as cultivars that exhibit a cooperation between leaf cell chloroplasts and mitochondria in the synthesis and maintenance of ascorbic acid in leaf cells. This also suggests that any genetic improvement on increasing levels of ascorbic acid in leaves is going to be more complicated than just increasing the activities of rate-limiting enzymes of the ascorbic acid synthesis pathway.
Understanding the various physiological aspects of tolerance of crop plants to ozone- induced stress is important for selecting the most appropriate cultivar and management practices. 6. What do you expect to accomplish, year by year, over the next 3 years? FY 2004 Continue to examine the influence of elevated CO2 exposure on the relationship between the photosynthetic carbon metabolism, photosynthate partitioning and the synthesis of ascorbic acid in the leaves of barley and wheat. Barley plant treatments will be conducted in high light growth chambers equipped with a system to permit manipulating the growth chamber CO2 levels. Examine the influence of elevated ozone on the relationship between photosynthetic carbon metabolism and photosynthate partitioning to support ascorbic acid synthesis. This work will be conducted in the leaves of a mutant of Arabidopsis thallania which has been genetically manipulated to have a deficiency in the carbon assimilatory pathway associated with
ascorbate synthesis and has low ascorbate. Other Arabidopsis mutants will be employed that have deficiencies in photosynthetic carbon assimilatory capacity. Much of this work will be conducted in collaboration with ARS-Alternate Crops and Systems Laboratory (R.C. Sicher), Beltsville, Maryland. FY 2005 Examine the enzymes of ascorbate synthesis pathway in leaves of sunflower infected with the organism Pseudomonas syringae pv tagetin to determine how tagetitoxin causes a reduction in foliar levels of ascorbate in infected leaves. Determine how hexose phosphate metabolism and partitioning to ascorbate has been affected by tagetitoxin. Examine the relationship between sunflower leaf ascorbate concentration, and gene expression in sunflower plants that are associated with the attempted defense against tagetitoxin attacks on chloroplast RNA synthesis enzymes, e.g. RNA polymerase. Much of this work will be conducted in collaboration with ARS-Sustainable Agricultural Systems Laboratory (J.
Lydon), Beltsville, Maryland. FY 2006 Develop techniques for the extraction and quantitation of soybean leaf lipid hydroperoxides and lipid hydroperoxide breakdown products such as malondialdehyde to use as markers for assessing ozone-induced and drought- induced oxidative stress in soybean leaves. Use soybean plants exposed to elevated ozone and/or drought stress in the green house and in the field to define the extent of oxidative stress caused by ozone and/or drought. This work will be conducted in collaboration with ARS-Alternate Crops Systems Laboratory (J. Bunce), Beltsville, Maryland. Develop techniques for extraction and measurement of protein sulfhydryl status and assess the protein sulfhydryl status to use as markers for oxidative stress in leaves of soybean plants exposed to elevated ozone or drought in the greenhouse and in the field. Develop methods for extraction and quantitation of enzymes of the ascorbate-glutathione cycle as well as the enzymes of the
photosynthetic pentose phosphate reductive cycle and enzymes of the oxidative pentose cycle in soybean cultivars. Measure the impact of drought-and/or ozone-induced oxidative stress on these enzyme systems and attempt to correlate protein sulfhydryl status with enzyme inhibitions caused by oxidative stress associated with elevated ozone and/or drought. This work will be conducted using soybean plants grown in the greenhouse and/or a field crop environment. 7. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? 1. Agricultural Research Service News release, entitled, "High Carbon Dioxide Levels Cause Stress in Barley," January 23, 2003, described the negative influence of elevated atmospheric carbon dioxide levels in causing young developing barley plant,
primary leaf to senescence concurrent with the decline in the foliar antioxidants ascorbic acid and glutathione. The information reported was used by Mr. Ken Thompson, a Northeastern Oregon Farmer as supporting evidence of the dangers of elevated CO2 to crop production in his presentation to farmers of that area concerning industrial related air pollution in Oregon entitled, "Airshed: Is It Important to Umatilla County, Oregon?," March 17, 2003. 2. A poster report, entitled, "Investigating the Role of cell wall phenolics in the differential sensitivity of two soybean cultivars to ozone," was presented at the 35th Air Pollution Workshop held in Vancouver, BC, Canada in April 2003. 3. An oral report, entitled, "Ascorbate redox status is associated with the tolerance of photosynthesis to elevated ozone in soybean," was presented at the Annual Meeting of the Multi-States Experiment Station Committee NE-1013, Mechanisms of Plant Responses to Ozone in the Northeastern United States, held
in Raleigh, N.C.
Impacts
(N/A)
Publications
- Robinson, J.M., Sicher, R.C. Antioxidant levels decline in primary leaves of barley during growth at ambient and elevated CO2. Plant Biology. 2003. Abstract No.131, p.56.
- Wiese, C.B., Robinson, J.M. Investigating the role of cell wall phenolics in the differential sensitivity of two soybean cultivars to ozone. 35th Air Pollution Workshop. 2003. Abstract p. 2.
|
Progress 10/01/01 to 09/30/02
Outputs
1. What major problem or issue is being resolved and how are you resolving it? Ozone (O3), a naturally occurring component of earth's atmosphere, is steadily rising in areas of the earth's troposphere due to human domestic and industrial activities. Unfortunately, tropospheric O3 is rising to very high levels in many North American agricultural areas. In the spring and summer growing seasons, levels of O3 often rise to as high as 40 to 150 nL L-1, and at these higher levels, O3 is phytotoxic. Ozone can cause damage to leaves of ornamental as well as horticultural and agronomic crops. It penetrates the plant foliage through the stomates into cell walls and then decomposes to highly-toxic, oxygen-containing molecules, such as superoxide radical, hydroxyl radical, peroxyradical, and hydrogen peroxide. These reactive oxygen molecules can damage plant cells resulting in the reduced vegetable, grain, and fruit yields. Global warming, another potential problem for U.S.
and the world's agriculture, is believed to contribute to the increasing frequency of drought-induced water stress of crops, resulting in tremendous losses in agricultural productivity and threatening the world food supply. Drought induced-water stress of crop plants inhibits photosynthesis which also leads to the increase of the toxic oxygen-containing molecules in the plant leaf cells, which in turn, leads to oxidative stress. ARS-Environmental Quality Laboratory scientists have shown the ability of leaf cells to maintain the antioxidant ascorbic acid (vitamin C) in the reduced (or active) state as a factor that assists soybean cultivars to be ozone tolerant and yield normally during season-long exposure to elevated ozone. We have also observed that during drought-induced water stress, the leaves of some cultivars of soybean and spinach are better able than others to maintain ascorbic acid as the reduced form, thus presumably assisting the plant leaf cells to cope with oxidative
stress caused by the internally generated toxic oxygen molecules. The major objective of this project is to determine the role of the oxidation-reduction turnover and synthesis of ascorbic acid (ASC) in relation to crop plant tolerance to oxidative stress, resulting from prolonged exposure to elevated tropospheric O3 and to drought-induced water stress. Differences in ascorbic acid oxidation-reduction and synthesis processes will be identified in various cultivars that could be genetically manipulated to improve crop plant tolerance to O3-induced and drought stress induced oxidative stress. Our research will be conducted in the greenhouse, in the field, as well as in the laboratory. The information produced in these studies will be important to plant geneticists and breeders developing crop cultivars tolerant of oxidative stress caused by elevated tropospheric ozone and/or drought-induced water stress. This information will benefit farmers, agribusinesses, consumers and
environmental lawmakers and policymakers. 2. How serious is the problem? Why does it matter? The crop losses due to ozone-induced oxidative stress are estimated to be in the millions of dollars to North American agriculture alone. Additionally, the recent increase in the duration in drought in North America has caused many areas of the United States to suffer extended periods of low water availability resulting in prolonged crop plant drought stress. This has led to very recent crop loss in the millions of acres in the central United States. For example, over the last four years, drought related wheat yield losses in some midwestern states, such as Kansas and eastern Colorado, have caused as much as a 30% decrease in yield. Understanding the various physiological aspects of tolerance of crop plants to ozone-induced and drought-induced water stress is important for selecting the most appropriate cultivar and management practices. Based upon recent environmental emergencies, more
basic information which will assist plant breeders in developing O3-tolerant and/or drought-tolerant cultivars of crops is urgently needed. 3. How does it relate to the national Program(s) and National Program Component(s) to which it has been assigned? This research supports National Program 203: Air Quality (60%), Component IV - Ozone Impacts and National Program 204: Global Climate Change (40%), Component III - Agricultural Ecosystems Impacts. 4. What was your most significant accomplishment this past year? 4A. Single most significant accomplishment during FY2002: Plants that accumulate the foliar ascorbate at a greater or lower normal level are being sought to understand the mechanisms by which ascorbic acid can be synthesized or degraded as well as to further characterize the role of ascorbic acid in assisting plants to tolerant oxidative stress caused by such stressors as ozone and drought. In collaboration with Dr. John Lydon (ARS-SASL, Beltsville), ascorbic acid relationships
were examined in sunflower plant leaves which have been infected with Pseudomonas syringae pv. tagetis; this produces the phytotoxin, tagetitoxin which inhibits the RNA polymerase of chloroplasts and prevents chloroplast formation and chlorophyll synthesis. Sunflower plants infected with Pseudomonas syringae pv. tagetis accumulated lower levels of ascorbic acid. Thus, Tagetitoxin may provide a tool to help us examine the role of ascorbate synthesis or ascorbate breakdown mechanisms in assisting plants to tolerate stresses such as ozone and drought exposures. 4B. Other significant accomplishments The influence of leaf ageing and elevated CO2 concentration on the primary leaf of developing barley seedlings was examined. In collaboration with Dr. Richard Sicher (ARS-ACSL Beltsville), ascorbic acid concentration in the barley primary leaves was found to steadily decline 38% over a period of 9 to 17 days after planting when grown in normal CO2 level. This is an important finding in regard
to the impact of elevated CO2 on global change aspects on plants because plants with decreasing foliar levels of ascorbic acid are more vulnerable to other stressors which cause oxidative stress in leaves, i.e., drought and ozone induced oxidative stress. 5. Describe your major accomplishments over the life of the project, including their predicted or actual impact? This is a new project initiated in April 13, 2002 and expands upon the work begun in the previous CRIS 1265-11120-006-00D, PHYTOCHEMICAL RESPONSES TO ENVIRONMENTAL STRESS: IMPLICATIONS FOR GLOBAL CHANGE AND NUTRITION. This new study will expand upon the work of the previous project. Tropospheric ozone is rising to very high levels in many North American agricultural areas and can cause damage to leaves of ornamental as well as horticultural and agronomic crops by penetrating the plant foliage, decomposing to highly-toxic, oxygen-containing molecules, thereby resulting in the reduced vegetable, grain, and fruit yields.
Drought induced-water stress of crop plants inhibits photosynthesis which also leads to the increase the toxic oxygen-containing molecules in the plant leaf cells; this, in turn, leads to oxidative stress. Previous studies showed that ascorbic acid (vitamin C) in the reduced (or active) state was a factor that assists soybean cultivars to be ozone tolerant and yield normally during season-long exposure to elevated ozone. During drought-induced water stress, the leaves of some cultivars of soybean and spinach are better able than others to maintain ascorbic acid as the reduced form, thus presumably assisting the plant leaf cells to cope with oxidative stress caused by the internally generated toxic oxygen molecules. Results indicated that photosynthesis is less vulnerable to elevated ozone in new fully-expanded soybean leaves than in older mature leaves, further suggesting that cells of younger leaves have a stronger antioxidant-capacity than older mature leaves. Other results
suggested that vernalization may help initiate an increase in antioxidant capacity as wheat leaves develop in the spring and summer, and the yearly cultivation practice of planting hard red winter wheat in the fall and letting the seed overwinter until spring may allow the wheat to develop ozone tolerance. 6. What do you expect to accomplish, year by year, over the next 3 years? FY2003 Develop extraction and measurement techniques for antioxidants including ascorbic acid (ASC), dehydroascorbate (DHA), reduced glutathione (GSH) and oxidized glutathione (GSSG) and the pyridine nucleotide cofactors [e. g. NAD(P) and NAD(P)(H)] from both symplastic and apoplastic extracts from leaves. Develop techniques for the extraction and quantitation for lipid hydroperoxides and lipid hydroperoxide breakdown products such as malondialdehyde which appear in leaf cells after prolonged periods of oxidative stress. Develop techniques for extraction and measurement of protein sulfhydryl status in the
symplast and apoplast of O3-exposed and drought exposed cultivars. Assess leaf cell lipid hydroperoxide and sulhydryl group status during ozone and drought stress of plants. Develop methods for extraction and quantitation of enzymes of the ascorbate-glutathione cycle as well as the enzymes pentose phosphate reductive cycle (PPRC enzymes) and oxidative cycle (PPOC enzymes) in soybean and spinach cultivar leaf apoplastic and symplastic fractions. Elucidate the influence of elevated ozone levels on the antioxidant relations and carbon assimilation relations in ozone tolerant and sensitive cultivars. Conduct experiments concerning oxidative stress response to differences in vegetative stages and leaf ages. Conduct experiments to discern how Tagetitoxin influences the synthesis and cycling of ascorbate acid in noninfected and tagetioxin infected sunflowers and soybean leaves. Toxin infected plants may be more ozone sensitive demonstrating the role of ascorbate in ozone tolerance.
Tagetitoxin infected soybean leaves will be subjected to elevated ozone. FY 2004 Assess ascorbic acid synthesis and cycling in barley and wheat exposed to elevated CO2. Develop extraction and measuring techniques for PPRC enzymes, e.g, ribulose-1,5-bisphosphate carboxylase/oxygenase, glyceraldehyde-3-phosphate dehydrogenase, and fructose-bisphosphatase. Conduct greenhouse studies with the spinach cultivars and soybean cultivars to examine the influence of oxidative stress from ozone and from drought on these enzymes. Carry out field experiments with soybean cultivars to discern the effects of vegetative stages and leaf ages. FY 2005 Continue experiment to examine mechanistic responses of spinach cultivars and soybean cultivars to ozone and drought conditions in the greenhouse and field study sites. Experiments will be carried out considering response differences in vegetative stages and leaf ages. 7. What technologies have been transferred and to whom? When is the technology likely
to become available to the end user (industry, farmer other scientist)? What are the constraints, if known, to the adoption durability of the technology? Provided information on research regarding ascorbic acid as an antioxidant in assisting plants to tolerate elevated ozone to Air Quality Task Force members during their visit to BARC. Presented information demonstrating that in studying plants for foliar mechanisms of ozone tolerance, it is important to examine both younger fully expanded leaves and older mature leaves, because the younger leaves may be more ozone tolerant than the mature leaves as leaves with repressed antioxidant capacity may be compared with leaves with more vigorous antioxidant capacity. This technology has been communicated to several scientist user groups. Provided information on research regarding atmospheric transport of pesticides to Air Quality Task Force members during their visit to BARC. Presented research and participated in two regional projects to
the Annual Meeting of the Multi-States Experiment Station Committee NE-176: MECHANISMS OF PLANT RESPONSES TO OZONE IN THE NORTHEASTERN US
Impacts
(N/A)
Publications
- Robinson, J.M., Rowland R.A. Influence of elevated ozone on photosynthesis and stomatal conductance in new, fully expanded and mature leaves of modern soybean cultivars Proceedings of the 34th Air Pollution Workshop at Pennsylvania State University, State College, Pennsylvania, Abstract S- 26.
|
|