chlorophyll-a and coronatine

Coronatine (COR) is a phytotoxin produced by Pseudomonas syringae. Its structure is similar to those of jasmonates (JAs), which play diverse roles in multiple plant biotic and abiotic defenses. However, the biological activity of COR is 1000 times greater than the activity of JA. In addition to being involved in the JA pathway, COR affects plant photosynthetic efficiency. In this study, we examined wheat blade pretreatment with COR. Blades treated with COR remained green longer than those of control plants under drought stress conditions, resulting in less yield loss with COR treatment. To investigate the mechanism of COR in drought resistance further, we employed two-dimensional gel electrophoresis technology and matrix-assisted laser desorption/ionization mass spectrometry to sequester and identify key proteins. Six COR-inducible proteins that are located in the chloroplast and involved directly in photosynthesis were found. The wheat homologue of protein gi|326509937 is degradation of periplasmic proteins 1 (DEGP1) in Arabidopsis, which is a response to photosystem II reparation, and was maintained at a low level with COR treatment. Finally, we measured levels of chlorophyll and photosynthetic performance to reveal the phenotypic effect of COR. Taken together, the results demonstrate that COR enhances drought tolerance by maintaining high photosynthetic performance.

Topics: Amino Acids; Chlorophyll; Chloroplasts; Droughts; Electrophoresis, Gel, Two-Dimensional; Gene Expression Regulation, Plant; Indenes; Photosynthesis; Plant Proteins; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Triticum

Coronatine (COR), a structural and functional mimic of jasmonates, is involved in a wide array of effects on plant development and defence responses. This study was conducted to explore the role of exogenously applied COR in alleviating the adversities of drought stress in soybean. COR treatment markedly increased the activities of antioxidant enzymes and proline content, and reduced the accumulation of malondialdehyde and hydrogen peroxide under drought stress. Thus, COR-treated plants had higher leaf relative water content and lower electrolye leakage, which led to higher chlorophyll content, activities of RuBPCase and PEPCase, and net photosynthetic rate compared to control plants exposed to drought. COR also increased maximal efficiency of PS II photochemical reaction and photochemical quenching coefficient, but decreased non-photochemical quenching coefficient. These beneficial effects led to enhanced photosynthetic performance and the translocation of assimilated (14)C which promoted growth and accumulation of dry biomass in COR-treated soybean plants subjected to drought. Interestingly, COR application did not affect the growth and biomass accumulation under well-watered condition. These results suggested the involvement of COR on improving drought tolerance in soybean by modulating antioxidant systems and membrane stability to maintain higher photosynthetic performance.

Topics: Amino Acids; Antioxidants; Biomass; Carbon Radioisotopes; Catalase; Chlorophyll; Droughts; Fluorescence; Glycine max; Hydrogen Peroxide; Indenes; Lipid Peroxidation; Malondialdehyde; Phosphoenolpyruvate Carboxylase; Photosynthesis; Plant Leaves; Plant Transpiration; Ribulose-Bisphosphate Carboxylase; Stress, Physiological; Water

Toxins are secondary metabolites produced by several plant pathogenic microorganisms. These toxins play a major role in the development of disease symptoms. Coronatine, the non specific toxin, was extracted and purified from the culture medium of Pseudomonas syringae pv. glycinea. In this study, the effect of coronatine on the development of the chlorotic lesion on the Phaseolus vulgaris L. leaves, indicates that coronatine induced chlorosis on treated leaves as well as or untreated leaves on the same plant. An other effect of this toxin is the reduction of amount of both chlorophyll a and b. These results, provide that the development of chlorotic lesion is a primarily mode of action of coronatine.

Topics: Amino Acids; Chlorophyll; Chlorophyll A; Indenes; Phaseolus; Plant Leaves; Pseudomonas

accelerated cell death 2 (acd2) mutants of Arabidopsis have spontaneous spreading cell death lesions and constitutive activation of defenses in the absence of pathogen infection. Lesion formation in acd2 plants can be triggered by the bacterial toxin coronatine through a light-dependent process. Coronatine-triggered and spontaneous lesion spreading in acd2 plants also requires protein translation, indicating that cell death occurs by an active process. We have cloned the ACD2 gene; its predicted product shows significant and extensive similarity to red chlorophyll catabolite reductase, which catalyzes one step in the breakdown of the porphyrin component of chlorophyll [Wüthrich, K. L., Bovet, L., Hunziger, P. E., Donnison, I. S. & Hörtensteiner, S. (2000) Plant J. 21, 189-198]. Consistent with this, ACD2 protein contains a predicted chloroplast transit peptide, is processed in vivo, and purifies with the chloroplast fraction in subcellular fractionation experiments. At some stages of development, ACD2 protein also purifies with the mitochondrial fraction. We hypothesize that cell death in acd2 plants is caused by the accumulation of chlorophyll breakdown products. Such catabolites might be specific triggers for cell death or they might induce cellular damage through their ability to absorb light and emit electrons that generate free radicals. In response to infection by Pseudomonas syringae, transgenic plants expressing excess ACD2 protein show reduced disease symptoms but not reduced growth of bacteria. Thus, breakdown products of chlorophyll may act to amplify the symptoms of disease, including cell death and yellowing. We suggest that economically important plants overexpressing ACD2 might also show increased tolerance to pathogens and might be useful for increasing crop yields.

Topics: Alleles; Amino Acids; Apoptosis Regulatory Proteins; Arabidopsis; Arabidopsis Proteins; Cell Death; Chlorophyll; Chloroplasts; Cloning, Molecular; Cycloheximide; DNA, Antisense; DNA, Complementary; Genes, Plant; Immunity, Innate; Indenes; Mitochondria; Molecular Sequence Data; Oxidoreductases; Phenotype; Plant Diseases; Plant Leaves; Plant Proteins; Plants, Genetically Modified; Protein Biosynthesis; Protein Synthesis Inhibitors; Pseudomonas; Reactive Oxygen Species