Differential organ-specific response to salt stress and water deficit in nodulated bean (Phaseolus vulgaris)

Nodulated bean plants were exposed to mild salt stress or water deficit in such a way that the nodule's nitrogen-fixing activity was reduced to about 25-30% that of controls. Water-deprived plants showed a slight decrease in the weight of the aerial part, whereas the photosynthetic parameters were not significantly affected. In contrast, salt-stressed plants displayed a reversible decrease in the quantum yield of photosystem II photochemistry. Five waterdeficit responsive cDNA clones encoding one lipid transfer protein, two late-embryo genesis abundant (LEA) proteins and two proline-rich proteins (PRPs) showed different organ-specific expression patterns depending on the kind of stress applied. PRPs and one LEA protein, PvLEA-18, exhibited the highest expression in nodules. Anti-PvLEA-18 antibodies were used to immunolocalize the protein in the nodule. PvLEA-18 was localized in the cytoplasm and nucleus of nodule cortex cells, and preferentially in cells of the vascular bundles, showing enhanced accumulation under water deficit. To our knowledge, this is the first time that a LEA protein has been identified in legume nodules.