Effect of Elevated Temperature on Premature Senescence in Nodules of Pea (Pisum sativum L.) sym26 and sym27 Mutants. I. Histological Organization and Expression of Marker Genes

Under global warming, understanding the response of legume crops to elevated temperature is essential to improve their stress tolerance, and, consequently, increase yields. In this study, the effect of elevated temperature on nodule senescence was examined in the pea (Pisum sativum L.) mutant lines SGEFix−-3 (sym26) and SGEFix−-7 (sym27) with an early nodule senescence phenotype and the wild-type SGE line. In nodules of the SGEFix−-3 (sym26) and SGEFix−-7 (sym27) mutant lines, in contrast to wild-type nodules, elevated temperature induced senescence in the apical part of nodule and enhanced senescence in the basal part already in 1 day of exposure. Expression levels of many analyzed genes associated with senescence, heat and defense responses were higher in heat-unstressed mutant nodules than in wild type. At the same time, in heat-stressed mutant nodules, the expression levels of these genes were significantly lower than in heat-unstressed mutant nodules. Moreover, in the SGEFix−-3 (sym26) mutant, expression levels were lower than in the SGEFix−-7 (sym27) mutant in both heat-stressed and heat-unstressed nodules. Likely, this decrease can be explained by the strong degradation of cells in the apical part of heat-stressed nodules in mutants, and in the SGEFix−-3 (sym26) mutant, it occurs more strongly. Thus, the study showed that nodule senescence induced by elevated temperature differs between the wild type and mutant lines. It seems that the cells of mutant lines SGEFix−-3 (sym26) and SGEFix−-7 (sym27) are characterized by increased sensitivity to elevated temperature, in comparison with wild-type cells, due to alteration of their homeostasis as a result of mutations.