Exogenous salicylic acid ameliorates short-term drought stress in mustard (Brassica juncea L.) seedlings by up-regulating the antioxidant defense and glyoxalase system

摘要

In this study, the protective role of salicylic acid (SA) in relation to the water status, chlorophyll content, antioxidant defense and glyoxalase system was investigated in drought stressed mustard (Brassica juncea L. cv. BARI Sharisha 11) seedlings. Two sets of 10-d-old seedlings were subjected to two different levels of drought (10% and 20% PEG, 48h), where one set of seedlings was supplemented with 50 μM SA. The relative water content (RWC), Chl b and Chl (a+b) decreased at any level of drought, while Chl a content decreased only at severe drought (20% PEG). Drought stress caused a sharp increase in proline (Pro) content. A sharp increase in malondialdehyde (MDA) and H2O2 was observed in both levels of stresses. Decline in AsA content and increase in GSH and GSSG content was observed at both levels of drought. Compared to control the activities of catalase (CAT) and monodehydroascorbate reductase (MDHAR) did not change due to drought stress. The activity of glutathione reductase (GR) slightly increased only at 10% PEG, while ascorbate peroxidase (APX) and glutathione S-transferase (GST) activity increased at any level of stress. The activities of glutathione peroxidase (GPX) and glyoxalase II (Gly II) decreased only at severe stress (20% PEG), while dehydroascorbate reductase (DHAR) and glyoxalase I (Gly I) activities decreased at any level of stress. Spraying with SA alone had little influence on the non-enzymatic antioxidants and the activities of antioxidant enzymes. However, supplementation of SA in drought stressed seedlings increased the RWC and Chl content, increased the AsA and GSH, decreased the GSSG content and maintained a higher ration of GSH/GSSG. Salicylic acid supplemented drought stressed seedlings also enhanced the activities of MDHAR, DHAR, GR, GPX, CAT, Gly I, and Gly II as compared to the drought-stressed plants without SA supplementation, with a concomitant decrease in H2O2, and lipid peroxidation level. These results suggest that the exogenous application of SA assisted the plants to become more tolerant to drought stress-induced oxidative damage by enhancing their antioxidant defense and glyoxalase systems.