Effects of exogenous spermidine on nitrogen metabolism of cucumber seedlings under high temperature stress

Taking the moderate heat-tolerant cucumber cultivar 'Jinchun 4' as test material,a quartz sand culture experiment was conducted in a growth chamber to investigate the effects of exogenous spermidine(Spd) on the nitrogen metabolism of cucumber seedlings under high temperature(42 ℃) stress.Short term high temperature stress,especially within 4 hours,decreased the plant nitrate N content while increased the plant ammonium N content,whereas pretreated with exogenous Spd increased the plant nitrate N and ammonium N contents and nitrate reductase(NR) activity.Longer term high temperature stress increased the root nitrate N content but blocked the nitrate N translocation to shoot,deactivated root NR activity,and increased the ammonium N content in root and leaf significantly.Foliar spraying Spd under high temperature stress promoted the nitrate N translocation from root to shoot,and increased the NR activity in root and leaf.From the viewpoint of long-term effect,exogenous Spd could have the effects of preventing the excessive accumulation of ammonium N in cucumber seedlings,and of promoting the normalization of the nitrogen metabolism of cucumber seedlings under high temperature stress.