外源褪黑素对高温胁迫条件下黄瓜幼苗氮代谢的影响

以‘津优4号’（热敏感型）和‘美国保尔’（耐热型）黄瓜幼苗为试材，研究了叶面喷施褪黑素对高温胁迫条件下黄瓜幼苗氮代谢的影响。结果显示，高温胁迫下，（1）两种黄瓜幼苗硝态氮含量先升高后降低，‘津优4号’总氮和氨态氮含量先下降后持续升高，而‘美国保尔’总氮和氨态氮含量持续上升；（2）两种黄瓜幼苗硝酸还原酶（NR）活性均先上升后下降，而谷氨酰胺合成酶（Gs）、谷氨酸合成酶（GOGAT）和谷氨酸脱氢酶（GDH）均持续下降，‘美国保尔’的4种酶活性下降幅度显著低于‘津优4号’。研究结果表明，叶面喷施褪黑素可有效缓解高温胁迫对NR、GS、GOGAT和GDH的抑制作用，显著增加硝态氮含量，降低氨态氮含量，减轻氨态氮积累对黄瓜幼苗造成的毒害作用，增强高温胁迫条件下黄瓜幼苗氮素的代谢能力，减轻高温胁迫对黄瓜幼苗造成的伤害，提高黄瓜幼苗抵御高温胁迫的能力。

Effects of Exogenous Melatonin on Nitrogen Metabolism in Cucumber Seedlings under High Temperature Stress

Effects of exogenous melatonin （MT） on the nitrogen metabolism under high temperature stress were investigated in cucumber seedlings, including a heat-sensitive cultivar （＇Jinyou No.4＇） and a heat-tolerant cultivar （＇American Baoer＇）. The results showed that under the stress of high temperature, the nitrate content in leaves of both cucumber cultivars increased firstly and then declined later. The total nitrogen or ammonium content in the leaves of ＇Jinyou No.4＇ declined firstly but increased constantly in ＇American Baoer＇. The activity of nitrate reductase （NR） increased firstly but then decreased later in the leaves of both cucumber cultivars, but the activities of glutamate synthase （GS）, glutamine synthetase （GOGAT） and glutamate dehydrogenase （GDH） decreased continually. All of the four enzyme activities in ＇American Baoer＇ decreased slower than those in ＇Jinyou No.4＇. The exogenous MT could significantly increase the activities of NR, GS, GOGAT and GDH, increased the nitrate content and restrained the accumulation of ammonium content under high temperature stress. These results indicate that exogenous MT could enhance the nitrogen metabolism of cucumber, reduce the damage of high temperature to the plants, and improve the resistance of cucumber seedlings against high temperature stress.