Abstract:

The purpose of this paper is to clarify the effect of gibberellin（GA）on the energy and carbon（C）skeleton supply of nitrogen（N）metabolism of cucumber（Cucumis sativus L.）under suboptimal root-zone temperatures and to provide some theoretic basis for searching an effective way to regulate the N use efficiency of cucumber.Cucumber seedlings at 2-leaf stage were treated with root-zone temperature（RT）22 ℃，RT 16 ℃ or RT 16 ℃ in the presence of 5 μmol · L^-1 GA₃（GA）for 8 d. Then the items，including individual plant dry mass，chlorophyll fluorescence parameters，photosynthesis parameters，activity of phosphoenolpyruvate carboxylase（PEPCase）and sucrose phosphate synthase（SPS），N and  C accumulation，and energy distribution between N and C metabolism were tested.The results showed that exposure of cucumber seedlings to a RT of 16 ℃ led to a significant reduction in the photochemistry activity of PSⅡ，O₂ evolution rate，activity of PEPCase and SPS，and energy distribution in N metabolism，while a rise in C/N. However，application of GA₃ showed prominent effects on mitigating the stress of suboptimal RT. Furthermore，GA treatment increased energy and C skeleton distribution in nitrogen metabolism. In conclusion，GA increased N absorption of cucumber under suboptimal RT conditions through increasing the energy and C skeleton supply.

Key words: cucumber, gibberellin, suboptimal root-zone temperature, nitrogen metabolism, energy；, carbon skeleton