[Effects of exogenous 24-epibrassinolide on the leaf photosynthetic characteristics and polyamines content of cucumber seedlings under hypoxia stress].

A water culture experiment with 1/2 Hoagland solution was carried out to study the effects of exogenous 24-epibrassinolide (EBR) on the leaf photosynthetic characteristics and polyamines (PAs) content of cucumber seedlings under hypoxia stress. Under the stress, the leaf net photosynthetic rate (Pn), stomatal conductance (g(s)), transpiration rate (Tr), and intercellular CO2 concentration (Ci) decreased significantly while the chlorophyll content was in adverse, and the seedling growth was inhibited. Hypoxia stress increased the leaf Put, Spd, and Spm contents and Put/PAs ratio significantly, but decreased the (Spd+Spm)/Put. Under the stress, exogenous EBR not only increased the Pn, g(s), Tr, and chlorophyll content significantly, but also increased the contents of free Spm, conjugated Spd and Spm, and bound Put, Spd, and Spm significantly. Meanwhile, the PAs content and (Spd + Spm)/Put ratio were further increased, and the Put/PAs ratio decreased. The results suggested that exogenous EBR could regulate the formation and form transformation of PAs in cucumber seedling leaf, made the leaf keep a higher photosynthetic performance, promote the increase of leaf area and dry mass, and alleviate the damage of hypoxia stress.