Abstract:

In the present study，we aimed to investigate the role of exogenous gibberellin（GA）on regulation of nitrate uptake in cucumber（Cucumis sativus L.）under suboptimal root-zone temperature. Cucumber seedlings with two true leaves were exposed to root-zone temperature（16 ℃）in the presence/ absence of 5 μmol · L-1 GA3. The time course of nitrate influx，expression pattern of nitrate transporter（NRT），nitrate reductase（NR），glutamine synthetase（GS），and glutamate synthetase（GOGAT）coding genes，and enzymes activities of NR，GS，and GOGAT，tissue NO3--N and total free amino acid concentration were quantified. The results showed that application of exogenous GA3 increased the 15NO3- influx and CsNRT1 gene expression gradually and simultaneously improved the activity and gene expression of key enzymes in N assimilation. Exogenous GA3 decreased the contents of NO3--N and total free amino acid firstly，but subsequently increased their concentration with time. These results indicate that enhancement of nitrate acquisition capacity of cucumber by GA3 application under suboptimal root-zone temperature may due to its positive effects on N assimilation，which clears the negative feedback signal of N-metabolites.

Key words: cucumber, suboptimal root-zone temperature, gibberellin, nitrogen metabolism, nitrogen uptake