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PROTECTIVE ROLES OF ALTERNATIVE OXIDASE PATHWAY IN PHOTOSYNTHESIS OF CUCUMBER LEAVES UNDER LOW TEMPERATURE AND WEAK LIGHT

In order to study the protective roles of alternative oxidase pathway in photosynthesis of cucumber leaves under low temperature(LT, 8 ℃) and weak light(100 μmol·m~(-2)·s~(-1)), a cucumber cultivar "Jinyan No. 4" was selected as experimental material, and the AOX inhibitor salicylhydroxamic acid(1 m M; SHAM) was used to inhibit AOX activity in vivo in both normal temperature(NT) and LT leaves. The results indicated that leaf AOX pathway was up-regulated after LT. Although net photosynthetic rate(P_n) decreased in leaves under LT, there were no change in photochemical reaction, thermal energy dissipation and photosynthetic electron transport were not changed. Also, LT was not influenced the energy distribution ratio between Y(II), Y(NPQ) and Y(NO). Inhibition of AOX pathway under LT decreased photochemical reaction and photosynthetic electron transport, and restricted P_n completely. However, photoinhbition did not occur because of the increase of thermal energy dissipation, which was induced by the down-regulation of AOX activity in leaves under LT. Taken together, up-regulation of AOX pathway would protect the photosynthetic electron transport chain and optimize photosynthesis in cucumber leaves under low temperature and weak light.