24-epibrassinolide and abscisic acid protect cucumber seedlings from chilling injury

A study investigated the ameliorative effects of the chill-induced inhibition of photosynthesis in cucumber by brassinolides and abscisic acid. Cucumber (Cucumis sativus L) seedlings at the three-leaf stage were sprayed with 24-epibrassinolide (EBS) and abscisic acid (ABA) at different concentrations. After chilling at 8degreesC, 4degreesC and 2degreesC for 3 d, the seedlings were allowed to recover under normal conditions. ABA and EBS pretreatments significantly alleviated chilling injury, increased the maximal photochemical efficiency (Fv/Fm) and net photosynthetic rate (Pn) of the chilled seedlings. Pn and apparent quantum yield of photosynthesis (QY) for seedlings chilled at 4degreesC declined to 40% and 39% of those for unchilled seedlings respectively, Pn and QY values for those pretreated with ABA and EBS, however, remained almost unchanged compared with those of unchilled seedlings.