一氧化氮对干旱胁迫下紫花苜蓿幼苗次生代谢产物的影响

Nitric oxide regulation of secondary metabolite accumulation in Medicago sativa seedlings under drought stress

本研究以盆栽紫花苜蓿为试验材料,在聚乙二醇(PEG-6000)模拟干旱的条件下,分别以硝普钠、c-PTIO(carboxy-PTIO)为NO供体和清除剂进行叶面喷施,通过研究紫花苜蓿幼苗叶片、根系中次生代谢产物及关键代谢酶活性的变化,探讨干旱胁迫对次生代谢产物的影响及NO介导下紫花苜蓿耐旱机制的响应。结果表明,干旱胁迫使紫花苜蓿叶片及根系中总酚、类黄酮、木质素和花青素的含量呈先升高后降低的变化趋势,同时增强了苯丙氨酸解氨酶(PAL)和多酚氧化酶(PPO)活性。外源NO的施加则会促进这种趋势的进行,使总酚含量提高33.08%,在胁迫后期仍使酚类物质保持较高的代谢水平,改善胁迫所导致的损伤状况。而NO抑制剂c-PTIO则会不同程度地抑制紫花苜蓿幼苗中酚类物质的合成及其代谢关键酶的活性。因此,外源NO的喷施使紫花苜蓿中次生代谢物的积累与抗氧化酶活性维持在一个高于仅干旱胁迫的水平,更大限度地降低干旱对紫花苜蓿造成的危害,提高对干旱的耐受性。本研究进一步扩充了紫花苜蓿抗旱手段的工具箱,对紫花苜蓿的抗旱具有重要的意义。

The aim of this study was to determine the effects of nitric oxide(NO)on the accumulation of metabolites and the activities of key metabolic enzymes in leaves and roots of drought-stressed alfalfa(Medicago sativa).The NO donor sodium nitroprusside and the NO scavenger carboxy-2-phenyl-4,4,5,5-tetramethylimidazolineoxyl-l-oxyl-3-oxide(c-PTIO)were applied as foliar sprays to potted alfalfa plants under simulated drought conditions(using polyethylene glycol-6000).The contents of total phenols,flavonoids,lignans,and anthocyanins increased and then decreased in the leaves and roots of alfalfa during the drought treatment,while the activities of phenylalanine aminolytic enzymes and polyphenol oxidase increased.These trends were promoted by application of exogenous NO,which increased the total phenolic content by 33.08%and led to higher phenolic contents during the late stages of drought stress,thereby reducing drought-induced damage.In contrast,application of the NO inhibitor c-PTIO inhibited the accumulation of phenolic compounds and reduced the activity of key metabolic enzymes in drought-stressed alfalfa seedlings.Thus,exogenous NO promoted the accumulation and retention of secondary metabolites and increased antioxidant enzyme activity in alfalfa to levels higher those under drought stress alone.This greatly reduced the severity of drought damage in alfalfa plants,and improved their drought tolerance.These findings improve our understanding of the plant response to drought stress,and highlight the potential use of an NO donor as a tool to improve the drought tolerance of alfalfa.