赤霉素对根区亚低温下黄瓜幼苗氮代谢与吸收的影响

为了探讨赤霉素（GA）对根区亚低温下黄瓜幼苗氮（N）吸收的影响机理，以营养液栽培的‘中农26’黄瓜为试材，研究了根施GA3对根区亚低温（16 ℃）胁迫下幼苗硝态氮（NO3--N）吸收速率、N代谢关键酶活性、NO3--N与总游离氨基酸含量、NO3--N转运蛋白（NRT）和N代谢酶的编码基因表达的影响。结果表明，在根区亚低温条件下，与未施用GA3的对照相比，施用5 μmol · L-1 GA3使黄瓜幼苗根系的15NO3-吸收速率显著提高，CsNRT1基因的表达水平也主要呈逐步增加的趋势，同时硝酸还原酶（NR）、谷氨酰胺合成酶（GS）和谷氨酸合成酶（GOGAT）活性与相应的编码基因的表达水平也主要呈逐步增加的趋势，而NO3--N和总游离氨基酸含量呈现先下降后上升的变化趋势。表明外源GA3通过促进N代谢，增加N需求的方式，提高了黄瓜在根区亚低温下的N吸收速率。

Effects of Gibberellin on Nitrogen Metabolism and Uptake of Cucumber Under Suboptimal Root-zone Temperature

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.