[Effects of exogenous salicylic acid and brassinolide on photosynthesis of cucumber seedlings under low temperature stress.] / æ°´æ¨é ¸å’Œæ²¹èœç´ å† é ¯å¯¹ä½Žæ¸©èƒè¿«ä¸‹é»„ç“œå¹¼è‹—å ‰åˆä½œç”¨çš„å½±å“.

ABSTRACT

An experiment was conducted to investigate the mechanism of the regulation of salicylic acid (SA) and 2,4-epibrassionolide (EBR) on photosynthesis in cucumber (Cucumis sativa) seedlings under low temperature stress. Taking cucumber cultivar 'Youbo1-5' as material, the seedlings were pre-treated with 1 mmol·L-1 SA or 0.1 µmol·L-1EBR (sprayed once a day), and then were exposed to chilling temperature (10 ℃/5 ℃, PFD 80 µmol·m-2·s-1) after being pre-treated 2 days. The results showed that the growth and net photosynthetic rate (Pn) of cucumber seedlings were decreased under low temperature stress. However, the Pn, maximal photochemical efficiency of PS2 (Fv/Fm), actual photochemical efficiency of PS2 (ΦPS2) and photochemical quenching coefficient (qP) were significantly improved in SA- and EBR-pretreated seedlings, and the increase range of non-photochemical quenching coefficient (NPQ) was decreased. Moreover, the activities of ribulose 1,5-biphosphate carboxylase/oxygenase (Rubisco), sedoheptulose-1,7-bisphosphatase (SBPase), fructose-1,6-bisphosphate aldolase (FBA) and transketolase (TK) were signi-ficantly increased. These findings suggested that SA and EBR improved photosynthesis of cucumber seedlings by promoting the activities of key enzymes and increased low temperature tolerance.