Progress 10/01/19 to 09/30/20
Outputs
Target Audience:A number of vegetable crops are affected by calcium deficiency disorders, especially tomato, apple, pepper and lettuce. Our research can benefit these industries by enabling the development of resistant varieties for them to grow in the future or development of more effective treatments to reduce the incidence of these disorders. In addition, researchers striving to understand calcium deficiency in plants are enabled by our research results to advance their studies. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The graduate student attended the American Society for Horticultural Sciences and the Institute of Food Technologists annual conferences and presented his research results at both conferences. He also entered a video contest describing his research results and was one of 3 finalist for the prize. How have the results been disseminated to communities of interest?Research results have been presented at the American Society for Horticultural Sciences and the Institute of Food Technologists annual conferences. One manuscript has been accepted for publication and a second journal article has been submitted for publication. A video describing the research highlights was prepared and submitted to a video conference under the Institute of Food Technologists. What do you plan to do during the next reporting period to accomplish the goals?We will continue our work with the disc system to enhance our understanding of the mechanism of blossom-end rot development. We will refine the concentration of calcium that can prevent blossom-end rot development and the timing that is and is not effective. In addition, we will finalize results for a microscopic technique to determine apoplastic calcium concentrations which is faster and less expensive than chemically assessing calcium content in extracted apoplastic solution.
Impacts
What was accomplished under these goals?
Investigate the role of oxidative stress, calcium signaling, and reactive oxygen signaling in BER development and increase understanding of the mechanism of calcium deficiency disorder development Increased lignin content was measured in tomato tissues showing blossom-end rot symptoms compared to comparable tissue in unaffected fruit. Lignification during blossom-end rot development was demonstrated to likely occurs through a peroxidase-mediated pathway. Hydrogen peroxide content was increased and catalase activity was reduced in blossom-end rot affected and adjacent tissues. A manuscript was published describing these results. Introduction of calcium solutions to tomato discs prevented the development of blossom-end rot symptoms and was concentration dependent. Introduction of ascorbic acid to tomato discs slowed the development of blossom-end rot symptoms, but was not as effective as calcium.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
do Amarante, C.V.T., J.P.G. Silvereira, C.A. Steffens, S.T. de Freitas, E.J. Mitcham, and A. Miqueloto. 2020. Post-bloom and preharvest treatment of Braeburn apple trees with prohexadione-calcium and GA4+7 affects vegetative growth and postharvest incidence of calcium-related physiological disorders and decay in the fruit. Scientia Hortic. 261, https://doi.org/10.1016/j.scienta.2019.108919.
- Type:
Journal Articles
Status:
Submitted
Year Published:
2021
Citation:
Reitz, N.F. and E.J. Mitcham. 2021. Lignification of tomato (Solanum lycopersicum) pericarp tissue during blossom-end rot development. Scientia Hortic. 276
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Progress 10/01/18 to 09/30/19
Outputs
Target Audience:Our research was primarily to benefit the fruit and vegetable industry, and specifically the tomato and apple industry who suffer from blossom end rot and bitter pit disorders. Our work is also of interest to extension specialists working with vegetables and fruit and the research community. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The PhD student presented his results at the annual meeting of the American Society for Horticultural Sciences and also attended a multistate project meeting in summer 2019. How have the results been disseminated to communities of interest?Presentation at the American Society for Horticultural Sciences conference. What do you plan to do during the next reporting period to accomplish the goals?We have developed a novel tomato disc system in which tomato tissues continue to develop BER after harvest. Tissue from the bottom of the tomato develop the disorder but those from the top do not, just like in the fruit on the plant. We plan to use this system to test the effect of a number of different compounds to enhance our understanding of BER development. We will also write up our results on lignin development with BER.
Impacts
What was accomplished under these goals?
1. Investigate the role of oxidative stress, calcium signaling, and reactive oxygen signaling in blossom end rot (BER) development. BER can be caused by low calcium or abiotic stresses, such as salt stress and water stress (drought stress). To test for conserved processes between these BER-inducing stresses, tomato plants were grown with low calcium ("Control"), low calcium plus salt stress ("Salt stress"), and low calcium plus drought stress ("Water stress"). To test the characteristics and effects of increased peroxidase activity in BER affected fruit, an in-depth investigation of peroxidase substrate specificity and localization was carried out. Results indicate that peroxidase activity was similar between healthy and BER-affected fruit when assayed with pyrogallol and ascorbic acid. This was shown for both the top and bottom healthy tissue in the fruit. When assayed with ferulic acid as an electron donor, peroxidase activity was increased in the bottom healthy tissue of BER affected fruit compared to bottom tissue from healthy fruit or the top of BER-affected fruit. An assay of peroxidase enzymes ionically bound to the cell wall exhibited similar results to that of the water-soluble ferulic acid peroxidase activity assay. 2. Increase understanding of the mechanisms of calcium deficiency disorder development Despite decades of research, the mechanism of cell death in BER remains unknown. Though considered a calcium deficiency disorder, recent research has shown that oxidative stress and interrupted cell expansion may also have a significant role in BER development. A thorough review of the literature shows that accumulation of hydrogen peroxide, increased peroxidase activity, upregulation of the phenylpropanoid pathway, and cell wall stiffening are all associated with BER development. This suggests that lignification may be the cause of cell wall stiffening and disrupted cell expansion. Catalase and peroxidase activity were assayed in BER-affected and healthy fruit 21 days after pollination. Catalase activity decreased and peroxidase activity increased in BER-affected fruit compared to control fruit. Ferulic acid is an analog of lignin precursors and increased ferulic acid peroxidase activity suggests that peroxidase activity in BER-affected tissues may result in lignification during BER development. Gene expression analysis showed upregulation of TPX1, a peroxidase gene associated with lignification, in BER-affected fruit. UV autofluorescence showed higher autofluorescence in BER-affected tissue. Toluidine blue O staining supported the autofluorescence data, with BER affected areas appearing green/blue and healthy tissue appearing violet. Lignification of expanding cells could result in disrupted cell expansion, which has been associated with BER development. Additionally, lignification may be indicative of conserved mechanisms between BER and other processes involving lignification and oxidative stress, such as chill injury, wound response, and pathogen response. Results from this project can be used to better inform breeders of BER-resistant tomatoes. 3. Identify mechanisms and tools to reduce development of calcium deficiency disorders. A large study with bitter pit in apples was conducted to explore use of growth regulators to control bitter pit development. Treatments were applied after full bloom, before harvest or postharvest, and including gibberellic acid, abscisic acid and a gibberellin biosynthesis inhibitor. Unfortunately, the tree to tree variability in bitter pit incidence masked the small differences observed between the treatments. However, the postharvest treatments showed an increase in bitter pit incidence from dipping apple fruit in distilled water. We are currently investigating the cause of this phenomenon.
Publications
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Progress 10/01/17 to 09/30/18
Outputs
Target Audience:This project targets the apple and tomato (fresh and processed) industries and researchers who work on calcium deficiency disorders. Changes/Problems:One of the major challenges to be overcome is development of reliable methods for fluorescence microscopy, with particular interest in quantifying fluorescence intensity. Consistent sample width, fluorescence probe infusion into the sample, and photobleaching are key factors in developing reliable methods. We are making progress in overcoming these challenges and expect to completely resolve the issues. What opportunities for training and professional development has the project provided?This project has provided a PhD student the opportunity to gain further knowledge and professional development in the specific area of postharvest handling. He has attended the University of Califronia Postharvest Technology of Horticultural Crops Short Course and the Fruit Ripening and Ethylene Management Workshops. He has also had the opportunity to network with industry officials throughcollaboration on projects and grant applications. How have the results been disseminated to communities of interest?Though final results have not yet been collected and disseminated, the collaboration with the processing tomato and apple industries have led to improved methods and further research. While discussing with processing tomato industry members, a highly susceptible variety of processing tomato was selected for further research in ongoing studies. This variety reliably produced BER with easily studied characteristic (i.e. an extended water soaked tissue stage prior to tissue dehydration or pathogen growth). Additionally, collaboration with members of the California apple industry helped identify bitter pit susceptible apple orchards for the study of postharvest treatments on bitter pit. What do you plan to do during the next reporting period to accomplish the goals?Tomato tissue will be collected from within the BER water-soaked area, adjacent healthy tissue, and upper pericarp healthy tissue to determine the effect of pericarp location on BER related processes. Preliminary results on catalase activity showed reduced activity at or near BER tissue compared to the upper pericarp and healthy. The effect of plant growth regulator treatments after harvest on bitter pit development was investigated in Granny Smith apples. Treatment were not shown to be effective. However, adequate samples were taken from bitter pit and non-bitter pit apples for further testing into the mechanism of bitter pit development. Current experiments are investigating the role of oxidative stress in bitter pit development, including reactive oxygen species localization using fluorescence microscopy and assays of oxidative stress related enzymes.
Impacts
What was accomplished under these goals?
1. Investigate the role of oxidative stress, calcium signaling, and reactive oxygen signaling in blossom end rot (BER) development Currently, we are investigating the link between oxidative stress, calcium, and reactive oxygen signaling in tomato BER development. Plants were grown with low calcium availability and exposed to salt, water stress, or control conditions. Water use and leaf water potential were measured. BER affected and healthy fruit were harvested at 3 time points. Enzyme activity assays of peroxidase, catalase, and lipoxygenase are in process to test for conserved processes under differing stress conditions. Preliminary results show conserved increases in peroxidase activity and gene expression in BER tissue compared with healthy fruit. This trend is conserved between total and ionically bound peroxidase. Fluorescence and histochemical staining microscopy have been used to investigate the presence and role of lignin in BER development. 2. Increase understanding of the mechanisms of calcium deficiency disorder development Current results show increased peroxidase activity in BER fruit compared to healthy fruit. This is observed in total peroxidase activity and peroxidases ionically bound to the cell wall. Additionally, this trend is conserved between salt stressed, water stressed, and control plants. Preliminary gene expression results show upregulation in BER fruit of peroxidases associated with lignification. A thorough review of the literature and preliminary histochemical staining suggests that lignification may play a role in restricting cell size in BER-affected fruit. The potential presence and role of lignin in BER tissue is being investigated. 3. Identify mechanisms and tools to reduce development of calcium deficiency disorders. The interaction of calcium and oxidative stress is under investigation during BER development to tomato, and may lead to new treatments to reduce BER. In apples, preharvest treatments of the plant growth regulators abscisic acid and Apogee were tested on apples for their effect on bitter pit development. These treatments, however, did not reduce bitter pit incidence in apple fruit. Further studies on samples taken from bitter pit affected and healthy tissue will increase understanding of processes related to cell death during bitter pit development and potentially lead to new treatments to reduce bitter pit.
Publications
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