Regulation effects of hydrogen sulfide on ascorbate-glutathione cycle in naked oat leaves under saline-alkali stress.

Saline-alkali stress is one of the common abiotic stresses for plants. Hydrogen sulfide (HS), as a gas signal, plays an important role in driving the responses of plants to saline-alkali stress. To explore the regulating effects of HS on the ascorbate (AsA)-glutathione (GSH) cycle in naked oat (Avena nude) under saline-alkali stress, we used sodium hydrogen sulfide (NaHS) as donor of exogenous HS and hydroxylamine (HA) as HS synthesis inhibitor to examine the effects of HS on plant growth, leaf reactive oxygen species, membrane lipid peroxidation, and antioxidants and key enzymes in the AsA-GSH cycle in "Dingyou 9" variety of naked oat under saline-alkali mixed stress. Results showed that spraying 50 μmol·L NaHS could alleviate the inhibition of 50 mmol·L saline-alkali mixed stress on the growth of naked oats, reduce the content of superoxide anions, HO, malondialdehyde, oxidized ascorbate (DHA), glutathione (GSH), and oxidized glutathione (GSSG) in leaves of naked oat under saline-alkali mixed stress, increase the ratio of AsA/DHA and GSH/GSSG, but did not affect the content of reduced ascorbic acid (AsA). Spraying NaHS significantly increased the activities of key enzymes, L-galactose dehydrogenase (GalDH) and L-galactono-1, 4-lactone dehydrogenase (GalLDH), for AsA synthesis pathways in naked oat leaves under salt-alkali mixed stress, as well as monodehydroascorbate reductase (MDHAR) in the AsA-GSH cycle, and decreased the activities of ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR), but did not affect the activities of ascorbate oxidase (AO) and glutathione reductase (GR). The addition of HA partially or completely relieved those aforementioned effects. Our results indicated that HS could increase the efficiency of AsA-GSH cycle by promoting the synthesis of AsA and enhancing the activity of MDHAR, and reduce the oxidative damage of saline-alkali stress to naked oats.