遮光下外源水杨酸对韭菜硝酸盐还原同化效应的研究

 【目的】通过研究不同光强下外源水杨酸（SA）对韭菜叶片硝酸盐（NO3-）累积、氮代谢关键酶活性、光系统II电子传递速率（ETR）及主要氨基酸和可溶性蛋白合成的调控效应，以期明确遮光水平下SA对硝酸盐还原同化的影响。【方法】以韭菜品种‘新世纪雪韭’为供试材料，在前期试验工作基础上，采用显著降低韭菜硝酸盐累积的3.0 mmol?L-1 SA对韭菜叶面进行喷施处理，设自然光（900—1 050 μmol?m-2?s-1）和遮光（40%自然光）2种光照强度，分析SA对韭菜硝酸盐累积及NO3-还原同化的影响。【结果】SA处理缓解了遮光水平下韭菜叶片氮代谢关键酶硝酸还原酶（NR）、谷氨酰胺合成酶（GS）、谷氨酸草酰乙酸转氨酶(GOT)和谷氨酸丙酮酸转氨酶（GPT）活性的降低，显著降低了硝酸盐的累积，其中，与弱光对照相比，SA处理下GOT活性和GPT增幅较明显，分别为23.7%和12.3%；SA处理还显著提高了弱光下叶片的全氮含量和干物率，但叶绿素含量和光系统间电子传递速率ETR的增幅不大；另外，SA处理增加了弱光下韭菜叶片多数游离氨基酸组分的含量，效果最为显著的为色氨酸和丝氨酸，分别比对照提高了89.8%和50.6%；并且提高了游离氨基酸总量和可溶性蛋白含量，但降低了游离氨基酸与可溶性蛋白比值A/P。【结论】弱光降低了韭菜氮素同化能力和物质生产能力，而SA处理促进了弱光下韭菜叶片氮代谢中硝酸盐的还原和铵的同化，同时调动转氨作用的积极协同配合，促进了硝态氮转化为游离氨基酸和可溶性蛋白，这可能是遮光下SA降低韭菜硝酸盐累积的一个重要原因。

Effects of Exogenous Salicylic Acid on Nitrate Reduction and Assimilation in Chinese Chive Under Weak Light

【Objective】The effect of exogenous salicylic acid (SA) on accumulation of nitrate, the key enzyme activity of nitrogen metabolism, the apparent electron transport rate (ETR) and the main amino acids and soluble protein was studied in Chinese chive under the weak light in order to understand the effects of exogenous salicylic acid on nitrate reduction and assimilation.【Method】With Chinese chive as an experimental material, two treatment factors  including SA (3.0 mmol?L-1) and light intensity (the weak light and natural light) were designed in the experiment. 【Result】Under the weak light, exogenous SA pretreatment reduced the decrease in the key enzyme activity of nitrogen metabolism (nitrate reductase (NR), glufamine synthetase (GS), glutamic- oxaloacetic-transaminase (GOT) and glutamate-pyruvate-transaminase (GPT)), while decreased nitrate accumulation. Compared with no SA treatments，NR and GS activities in SA treatments increased significantly , 23.7% and 12.3%, respectively. Also, the content of chlorophyll (Chl), ETR , the content of free amino acids and soluble protein of weak light were enhanced after SA application. In addition, SA increased the content of most free amino acid components under weak light, with tryptophan and serine as the most effective, reaching 89.8% and 50.6%, respectively, and at the same time reduced the free amino acids and soluble protein ratio (A/P). 【Conclusion】Weak light reduced the capacity of the nitrogen assimilation and material production, however, exogenous SA spraying on leaves obviously improved nitrate reduction and assimilation, which, meanwhile, brought transaminations into play vigorously, and promoted turning NO3- into free amino acid and dissolvable protein. Improvement of nitrate reduction and assimilation might be a key reason for reducing nitrate accumulating into the vacuole of Chinese chive under weak light.