Regulation of Senescence of Excised Leaves of Some C3 and C4 Species by Endogenous H2O2

Abstract

Endogenous level of hydrogen peroxide (H 2 O 2 ), metabolized via glycolate oxidation, was different in Oryza sativa (cv. Java), Vigna catjang (cv. Pusa barshati) and Triticum vulgare (cv, Sonalika) (all C 3 species) and in Zea mays (cv. Ganga-safeda), Cyperus rotundus and Amaranthus viridis (all C 4 species). Amaranthus , a C 4 species, showed an intermediate state in this respect. The senescerance of excised leaf segments was earlier in C 3 than in C 4 species after 4 d of incubation either in light or darkness. Light incubation delayed senescence in all six species compared to dark. Increase in H 2 O 2 metabolism via glycolate pathway was more pronounced in the dark than in light and the C 3 species showed significantly higher H 2 O 2 metabolism than the C 4 species, excluding Amaranthus . Treatments of leaf segments with α-HPMS (inhibitor of glycolate oxidase) under both light and dark conditions showed that glycolate oxidase was inhibited and H 2 O 2 production was markedly reduced leading to inhibition of senescence. This inhibition was more prominent in light and in C 3 species. Treatments of leaf segments with aminotriazole (inhibitor of catalase) significantly increased H 2 O 2 level and promoted senescence of leaves of all types of plants in the dark but the effect was more pronounced in C 3 species than in C 4 . Amaranthus , however, showed an intermediate picture in both treatments. Leaf segments pretreated with antioxidants (L-cystcine, and reduced-glutathione) delayed senescence in both categories of plants but the effect Was more pronounced in C 3 species and also in Amaranthus . Thus it was concluded that H 2 O 2 produced via glycolate pathway in C 3 plants plays a significant role in leaf senescence and C 4 species are less responsive to H 2 O 2 probably due to some inherent adaptive characteristics in them.