黄土高原冰草叶片抗坏血酸和谷胱甘肽合成及循环代谢对干旱胁迫的生理响应

Responses to drought stress of the biosynthetic and recycling metabolism of glutathione and ascorbate in Agropyron cristatum leaves on the Loess Plateau of China

通过盆栽实验,对干旱胁迫下黄土高原地区冰草(Agropyron cristatum)叶片的抗坏血酸和谷胱甘肽合成及循环代谢相关酶及物质含量进行了研究。结果表明:冰草可以通过增强叶片的抗坏血酸和谷胱甘肽合成及循环代谢酶:抗坏血酸过氧化物酶、谷胱甘肽还原酶、脱氢抗坏血酸还原酶、单脱氢抗坏血酸还原酶、L-半乳糖酸-1,4-内酯脱氢酶和γ-谷氨酰半胱氨酸合成酶活性,维持植物体内抗坏血酸和谷胱甘肽水平及氧化还原状态,从而抵御干旱造成的氧化胁迫。但叶片抗坏血酸和谷胱甘肽合成及循环代谢对不同水平干旱胁迫的响应,随胁迫时间的延长而不同。在胁迫24天以前,严重干旱下叶片的抗坏血酸和谷胱甘肽合成及循环代谢增强较显著;在胁迫24天后,由于该胁迫下植物所遭受的氧化胁迫较为严重,叶片中上述6种酶的活性均呈降低趋势。而在中度干旱下叶片抗坏血酸和谷胱甘肽合成及循环代谢相关的6种酶在整个胁迫过程中均保持较高的活性。这说明,冰草能够长时间有效地抵御中度干旱所造成的氧化胁迫,但只能在一定时间范围内有效地抵御严重干旱所造成的氧化胁迫,胁迫时间延长则会降低其抵御严重干旱的能力。

Aims Our objective was to clarify the mechanism of drought tolerance for Agropyron cristatum on the Loess Plateau of China through investigation of drought stress on the biosynthetic and recycling metabolism of glutathione and ascorbate in leaves. Methods We investigated the levels and redox status of glutathione and ascorbate and the activities of galactonolactone dehydrogenase （GalLDH）, gamma glutamyl cysteine synthetase （γ-ECS）, ascorbate peroxidase glutathione reductase （APX）, glutathione reductase （GR）, dehydroascorbate reductase （DHAR） and monodehydroascorbate reductase （MDHAR） in the leaves of A. cristatum under different levels of artificial drought stress using pot experiments. Important findings Levels of glutathione and ascorbate and their redox status were maintained under drought stress by increasing activities of GalLDH, γ-ECS, APX, GR, DHAR and MDHAR involved in the metabolism of glutathione and ascorbate. This protected A. cristatum from oxidative damage induced by drought stress. However, there were differences in the responses of the metabolism of glutathione and ascorbate related to different drought stress levels with prolonged stress. With 24 or fewer days of stress treatment, the metabolism of glutathione and ascorbate was enhanced under severe drought stress. After 24 days of stress treatment, the activities of GalLDH, γ-ECS, APX, GR, DHAR and MDHAR decreased significantly under severe drought stress, because A. cristatum suffered more severe oxidative damage. However, the activities of these enzymes were maintained throughout the whole period of stress under moderate drought stress. This suggested that A. cristatum could effectively protect itself from oxidative damage induced by moderate drought stress for long time periods. However, A. cristatum could only effectively protect itself from oxidative damage induced by severe drought stress for limited time, and its antioxidant capacity decreased significantly with prolonged stress. Our results also suggested that ascorbate and glutathione had important roles in protecting against oxidative damage under drought stress.