Progress 10/01/03 to 09/30/08
Outputs
OUTPUTS: A novel technique to explore recalcitrant seed death was developed by comparing three species within the same genus (Spartina) that exhibit differential seed desiccation tolerance. Novel computational procedures were developed to predict red rice germination in response to soil water potential and temperature as a function of the depth of seed dormancy. Organic solvent infusion procedures were optimized for permeation of signal transduction inhibitors into dormant red rice seeds. Collaborations were initiated to assess global gene expression changes in dormant and nondormant red rice seeds. Four doctoral students and 2 undergraduates were mentored during the study period. Dissemination of results: Graduate students presented award-winning talks at regional, national and international meetings. Investigator presented invited talks on dormancy and recalcitrance at 3 international meetings and 2 US universities. Peer-reviewed journal articles, book chapters, abstracts, and popular press articles were used to disseminate results obtained. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Study of the differential behavior of Spartina species to desiccation allowed us to exclude oxidative stress as the cause of recalcitrant seed death. Indicators previously associated with oxidative stress were observed in both orthodox and recalcitrant seeds during desiccation in the laboratory and in plants in the field. Modeling response of red rice seed dormancy as a function of depth of dormancy, soil water potential, and germination temperature was consistent with field environmental conditions under which dormancy is broken. Putative protein synthesis inhibitors may act by means other than translational interference during dormancy-breaking of red rice. Solvents previously thought to be innocuous may interact in combination with dormancy-breaking chemicals to interfere with germination.
Publications
- Cohn, M.A. 2008. Seed development, dormancy and germination. Annual Plant Reviews 27. Bradford, K.B. and Nonogaki, H. (Eds). Ann Bot 102:877-878 (Book review)
- Gianinetti, A., and Cohn, M.A. 2008. Seed dormancy in red rice. XIII. Interaction of dry afterripening and hydration temperature. Seed Science Research 18: 151-159.
- Chappell, J.H., and Cohn, M.A. 2008. Exploring recalcitrant seed death with the Spartina model system. Polish Journal of Natural Sciences, Supplement 5, p. 75.
- Chappell, J.H. and Cohn, M.A. 2007. Is oxidative stress the cause of recalcitrant seed death in Spartina alterniflora South African Journal of Botany 73: 482-483.
- Chappell, J.H. and Cohn, M.A. 2007. Is oxidative stress the cause of recalcitrant seed death Agronomy Abstracts Online.
- Gianinetti, A., and Cohn, M.A. 2007. Seed dormancy in red rice. XII. Population based analysis of afterripening with a hydrotime model. Seed Science Research 17: 253-271.
- Cohn M.A., and Chappell, J.H. 2007. Recalcitrance and dormancy in smooth cordgrass seeds. Louisiana Agriculture, 50 (2), 25.
- Cohn, M.A. 2006. Dormancy. pp. 177-181 in Black, M.; Bewley, J.D.; Halmer, P. (eds) The Encyclopedia of Seeds. Science, Technology and Uses. CABI Publishing, Wallingford, England.
- Kucera, B., Cohn, M.A., Leubner-Metzger, G. 2005. Plant hormone interactions during seed dormancy release and germination. Seed Science Research 15: 281-307.
- Cohn, M.A. 2004. Physiology of dormancy breaking mechanisms in red rice. Abstract S22MT20BP01. 4th International Weed Science Congress, Durban, South Africa). p. 75.
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Progress 01/01/07 to 12/31/07
Outputs
(1) A novel technique to explore recalcitrant seed death was developed by comparing three species within the same genus (Spartina) that exhibit differential seed desiccation tolerance. Summaries of these activities were disseminated and discussed at international, national and regional symposia and conferences. (2) A novel computational procedure was developed to predict red rice germination in response to soil water potential as a function of depth of seed dormancy; this protocol was disseminated through peer-reviewed publication to the seed and weed biology communities. (3) Three doctoral students and one visiting scientist were mentored under these programs.
Impacts
In Spartina species, maturation drying in the field or post-harvest flash drying increased protein carbonylation (oxidation); therefore, protein carbonylation is a normal event during seed maturation and is not related to seed desiccation tolerance. The total water-soluble antioxidant titer of Spartina seeds (desiccation tolerant and intolerant species) decreases during field maturation or laboratory drying, and is not associated with the recalcitrant behavior of Spartina alterniflora seeds. DNA fragmentation does not occur during Spartina alterniflora seed death due to drying. Fragmentation does occur after these dead seeds are stored for several months. The impact of these findings is that oxidative stress is not the cause of recalcitrant seed death in Spartina, representing a change of knowledge. The successful results of this comparative physiological approach represents a change of action strategy that will be necessary for proper interpretation of results
concerning recalcitrant seed research. Research on the mechanisms of recalcitrant seed death due to drying will help to identify the biophysical, biochemical and genetic factors governing seed desiccation tolerance and longevity. Such knowledge will globally improve our ability to genetically conserve important native and agricultural species, whose seeds are killed by drying. In addition, for Spartina alterniflora in particular, these results suggest potential strategies for seed preservation of this species to enable large-scale field establishment from seed.
Publications
- Chappell, J.H. and Cohn,M.A. 2007. Is oxidative stress the cause of recalcitrant seed death in Spartina alterniflora? South African Journal of Botany 73:482-483.
- Chappell, J.H. and Cohn, M.A. 2007. Is oxidative stress the cause of recalcitrant seed death in Spartina alterniflora? Agronomy Abstracts 69-3. [http://a-c-s.confex.com/crops/2007 am/techprogram/P34144.HTM]
- Cohn, M,A. 2007. Dormancy: An overview. in Black M; Bewley JD; Halmer P (Eds) Encyclopedia of seeds. Science, technology and uses. Wallingford, CABI Publishing
- Cohn, M.A. and Chappell, J.H. 2007. Recalcitrance and dormancy in smooth cordgrass seeds. Louisiana Agriculture 50 (2): 25.
- Gianinetti, A. and Cohn, M.A. 2007. Seed dormancy in red rice. XII. Population based analysis of afterripening with a hydrotime model. Seed Science Research 17: 253-271
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Progress 01/01/06 to 12/31/06
Outputs
Organic solvent infusion for permeation of signal transduction inhibitors in red rice caryopsis was optimized. Neat dimethylsulfoxide (DMSO), dichloromethane, methanol and ethanol were either toxic or broke dormancy when applied for 1-24 h. Neat acetone infusion for 24 h did not kill the seeds or break dormancy. In aqueous solution, DMSO inhibited the dormancy-breaking activity of propanol; this was consistent with the alcohol dehydrogenase-inhibiting property of DMSO. These data are consistent with previous observations showing that dormancy-breaking alcohols act as pro-drugs requiring metabolism for dormancy-breaking activity. Aqueous solutions of genistein, provided as a 24 hour pulse at the start of imbibition, broke dormancy of red rice. Red rice seeds were used as a model to study the mechanisms of seed dormancy in grassy weeds. Taking advantage of the fully sequenced genome of cultivated rice, microarray studies were initiated in collaboration with Dr. F. Chen
(University of Tennessee) to assess global gene expression changes in dormant red rice compared with red rice seeds treated with dormancy-breaking nitrogen oxides.
Impacts
This research contributes to the overall goals of the W-1168 Regional Project, which focuses upon elucidation of the environmental and genetic determinants of seed quality and performance. Ongoing research on the mechanisms of seed dormancy will define molecular signal transduction pathways that control seed germination in weeds and will provide new potential seed-focused weed control strategies.
Publications
- Cohn, M.A. 2006. Seed dormancy and germination. In R. Rose, S. McCammon and S. Lively (Eds) Proceedings of the Workshop On Confinement Of Genetically Engineered Crops During Field Testing. Biotechnology Regulatory Services, APHIS-USDA, Washington, D.C.
- Cohn, M.A. 2006. Dormancy: an overview. In M. Black, J.D. Bewley, P. Halmer (Eds) Encyclopedia of Seeds: Science, Technology and Uses. CABI Publishing, Wallingford, U.K.
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Progress 01/01/05 to 12/31/05
Outputs
The experimental system compares the seed drying of recalcitrant Spartina alterniflora (SA) with the desiccation-tolerant Spartina pectinata (SP), both in the dormant and non-dormant states. The contribution of secondary products of lipid oxidation to seed death was evaluated by assay of thiobarbituric acid-reactive substances (TBARS). When the TBARS assay was performed in the standard manner, lipid oxidation increased with drying in both Spartina species. However, when seeds were first freeze-clamped in liquid nitrogen prior to extraction, only low baseline amounts of TBARS were detected, and there was no effect of desiccation. Without corrections for interfering sugars and flavonoids, the baseline TBARS levels of SA seeds were greater than SP seeds. However, after removal of these interfering substances, there were no quantitative differences in TBARS between species at any time during drying. The dormancy status of SA seeds had no influence upon its recalcitrant
behavior or TBARS amounts during desiccation. Therefore, secondary metabolites generated by lipid oxidation are not associated with seed death due to recalcitrance, and prior claims in the literature for such a relationship may be artifactual due to a lack of proper precautionary procedures during tissue homogenization.
Impacts
This research contributes to the overall goals of the W-1168 regional project, which focuses upon elucidation of the environmental and genetic determinants of seed quality and performance. Current research on the mechanisms of death due to drying of the recalcitrant seeds of Spartina alterniflora will help to identify the biophysical, biochemical and genetic factors governing seed desiccation tolerance and longevity. Such knowledge will improve our ability to genetically conserve important native and agricultural species, whose seeds are killed by drying.
Publications
- Kucera, B., M.A. Cohn, G. Leubner-Metzger. 2005. Plant hormone interactions during seed dormancy release and germination (Invited Review) Seed Science Research 15: 281-307.
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Progress 01/01/04 to 12/31/04
Outputs
This research contributes to the overall goals of the W-1168 regional project, focusing upon elucidation of the environmental and genetic determinants of seed quality and performance. It is an open question as to whether or not continual translational activity (protein synthesis) is required to maintain seeds in the dormant state. It is not known if proteins that are required to induce dormancy are the same as those that may be required to maintain dormancy after a seed is shed from the mother plant. A chemical genetics approach was initially taken to determine if protein synthesis inhibitors break dormancy of red rice caryopses (naked seeds). (1) Extensive bioassay experiments revealed that cycloheximide (CHX), an inhibitor of eukaryotic protein synthesis, readily broke dormancy when applied as a 24-hour pulse treatment; prolonged exposure to CHX (3-5 days) resulted in seed death or seedling injury. CHX inhibited germination of afterripened, non-dormant seeds.
Therefore, while CHX breaks dormancy, it inhibits germination, implying that different sets of proteins may regulate the two processes. (2) In contrast, other eukaryotic (emetine, anisomycin) and the prokaryotic translational inhibitors, chloroamphenicol (CHL) and tetracycline (TET), did not break dormancy. Geneticin and hygromycin B, cross-kingdom translation inhibitors, were also inactive. While these chemicals did not break dormancy, seed viability after treatment was 90%, compared to 94% for the untreated controls. Seedlings grown from treated seeds, after mechanical breaking of dormancy, were normal. (3) The effect of solution pH upon the activity of emetine was determined. Emetine solutions adjusted to pKa 2 or one pH unit above pKa 2 did not break dormancy but did inhibit seedling growth of fully afterripened, non-dormant seeds. Therefore, it is possible that emetine was taken up by dormant seeds but had no physiological effect. (4) TET was inactive over the pH range of 3 to 7
and did not affect seedling growth; these results are consistent with the charged nature of TET across the range of physiological pH (likely preventing seed uptake) and/or its specificity for only prokaryotic translational machinery. Similar results were obtained for CHL. (5) While CHX is commonly employed in contemporary biological experimentation as a specific inhibitor of protein synthesis, an extensive literature review suggested that this is not the case. It is highly possible that CHX breaks dormancy by a means other than translational inhibition. Therefore, it is tentatively concluded from the overall data set that new protein synthesis is not required to maintain seed dormancy in red rice, but rather the controlling proteins are synthesized during grain development and are stabilized in the seed after it is shed from the mother plant. The potential implications of these data for interpretation of future genomic and proteomic are highly significant.
Impacts
The results enhance our understanding of the physiological factors that control whether weed or native plant seeds germinate or remain dormant in the soil. Identification of new physiological factors increases the range of seed components that can serve as targets for the design of new, environmentally benign, weed control treatments, or modification of cultural practices.
Publications
- Cohn, M.A. 2004. Physiology of dormancy-breaking mechanisms in red rice (invited symposium talk). Abstract S22MT20BP01, 4th International Weed Science Congress, Durban, South Africa. p. 75.
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