赤霉素对根区亚低温下黄瓜幼苗氮代谢与吸收的影响

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

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GA_3对根区亚低温(16℃)胁迫下幼苗硝态氮(NO_3^--N)吸收速率、N代谢关键酶活性、NO_3^--N与总游离氨基酸含量、NO_3^--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GA_3的对照相比,施用5μmol·L-1 GA_3使黄瓜幼苗根系的^(15)NO_3^-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NO_3^--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GA_3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。

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.