Effects of exogenous glutathione on glutathione metabolism in pakchoi under sulfur deficiency

Objectives Sulfur is essential for plant growth and development. Sulfur deficiency causes severe growth retardation of plants which in turn leads to poor crop production. Thus, there is need for studies on how to reduce the adverse effects of sulfur deficiency. In this study, we investigated the effects of exogenous glutathione (GSH) on GSH metabolism of pakchoi under sulfur deficiency.

Methods Pakchoi (Brassica rapa L.ssp. Chinensis var. communis. cv. Hangzhou You Dong Er) seedlings were grown in hydroponic medium for 17days under normal or sulfur deficiency. Then the seedlings under sulfur deficiency were subjected to three foliar spraying treatments: distilled water (H₂O), 25 mg/L of glutathione (GSH) and 25 mg/L of oxidized glutathione (GSSG), and the pakchoi seedlings grown in normal sulfur medium were sprayed with distilled water and used as control (CK).The leaf samples were collected at 0, 2, 4, 8 and 24 h after treatment to assess the expression of BcGSH1, and the leaf samples collected at 0, 24, 48 and 72 h to measure the activity of γ-glutamylcysteine synthetase (γ-ECs), glutathione reductase (GR), glutathione peroxidase (GPx), glutathione sulfur transferase (GST) and the content of GSH and GSSG.

Results Compared with CK, sulfur deficiency significantly reduced the expression of BcGSH1, GSH content, γ-ECs, GR, and GST activities, and increased the activity of GPx. Exogenous GSH significantly increased the GSH content, γ-ECs, GR, GPx and GST activities of pakchoi under sulfur deficiency. Spraying of GSSG increased GSH content, GSSG content, γ-ECs activity, GR and GST activities, but decreased GPx activity.

Conclusions Sprayed GSH and GSSG could be absorbed by pakchoi under sulfur deficiency. GSSG-induced increase in activities of GR, GST and decrease in that of GPx could alleviate the negative effects of sulfur deficiency on pakchoi.