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Published on January 24, 2008; 10.1104/pp.107.114066

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Received November 28, 2007
Accepted January 17, 2008

Ascorbate and Homoglutathione Metabolism in Common Bean Nodules Under Stress Conditions and During Natural Senescence

Jorge Loscos , Manuel A. Matamoros , and Manuel Becana *

Departamento de Nutricion Vegetal, Estacion Experimental de Aula Dei, Consejo Superior de Investigaciones Cientificas, Apartado 202, 50080 Zaragoza, Spain

* Corresponding author; email: becana{at}eead.csic.es.

Ascorbate and glutathione are major antioxidants and redox buffers in plant cells but also play key functions in growth, development, and stress responses. We have studied the regulation of ascorbate and homoglutathione biosynthesis in common bean (Phaseolus vulgaris) nodules under stress conditions and during aging. The expression of five genes of the major ascorbate biosynthetic pathway was analyzed in nodules and evidence was found that L-galactono-1,4-lactone dehydrogenase, the last committed step of the pathway, is posttranscriptionally regulated. Also, in nodules under stress conditions, {gamma}-glutamylcysteine synthetase was translationally regulated but homoglutathione synthetase (mRNA and activity) and homoglutathione (content and redox state) were not affected. Most interestingly, in nodules exposed to jasmonic acid, dehydroascorbate reductase activity was posttranslationally suppressed, ascorbate oxidase showed strong transcriptional up-regulation, and dehydroascorbate content increased moderately. These changes were not due to a direct effect of jasmonic acid on the enzyme activities but might be part of the signaling pathway in the response of nodules to stress. We determined ascorbate, homoglutathione, and ascorbate-glutathione pathway enzyme activities in two senescing stages of nodules undergoing oxidative stress. When all parameters were expressed on a nodule fresh weight basis, we found that in the first stage ascorbate decreased by 60% and homoglutathione and antioxidant activities remained fairly constant, whereas in the second stage ascorbate and homoglutathione, their redox states, and their associated enzyme activities significantly decreased. The coexistence of nodules at different senescence stages in the same plants, with different ascorbate concentrations and redox states, indicates that the life span of nodules is in part controlled by endogenous factors and points to ascorbate as one of the key players.




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