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

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.