Decreased TK activity alters growth, yield and tolerance to low temperature and low light intensity in transgenic cucumber plants

Four CsTK antisense transgenic cucumber plants were obtained. Decreased TK activity decreased the photosynthetic rate, seed germination rate, growth yield, and the tolerance to low temperature and weak light stress. Transketolase (TK, EC 2.2.1.1) is a key enzyme in the photosynthetic carbon reduction cycle (Calvin cycle). A cDNA fragment (526 bp) encoding transketolase was cloned from cucumber plants (Cucumis sativa L. cv 'Jinyou 3') by RT-PCR. The antisense expression [(PBI-CsTK(-)] vector containing the CsTK gene fragment was constructed. The resulting plasmid was introduced into the cucumber inbred lines '08-1' using the agrobacterium-mediated method, and four antisense transgenic cucumber plants were obtained. Decreased CsTK expression either unaltered or slightly increased the mRNA abundance and activities of the other main enzymes in the Calvin cycle, however, it decreased the TK activity and net photosynthetic rate (Pn) in antisense transgenic cucumber leaves. Antisense plants showed decreases in the growth, ratio of female flowers and yield compared with the wild-type (WT) plants. The decrease in Pn, stomatal conductance (Gs), transpiration rate (Tr), photochemical efficiency (F-v/F-m) and actual photochemical efficiency of PSII (I broken vertical bar(PSII)) and the increase in electrolyte leakage (EL) were greater in antisense transgenic plants than in WT plants under low temperature (5 A degrees C) and low light intensity (100 mu mol m(-2) s(-1)).