Heat-shock positively modulates oxidative protection of salt and drought-stressed mustard (Brassica campestries L.) seedlings

A large number of studies have shown the existence of cross-tolerance in plants, but the exact physiological and biochemical mechanism(s) is poorly understood. In this study, heat-shock (42 °C, 5 h) induced salinity and drought tolerance and possible involvement of antioxidative and glyoxalase systems were investigated in mustard (Brassica campestris L.) seedlings. Seven-day-old seedlings were subjected to salt (150 mM NaCl, 48 h) and drought stress (induced by 20% PEG, 48 h) with or without heat pretreatment. Both salt and drought stresses led to a severe oxidative stress as indicated by profound increases in hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels. A significant increase in ascorbate (AsA) content was observed in response to drought stress but the glutathione (GSH) and glutathione disulfide (GSSG) contents increased in response to both salt and drought stress. The GSH/GSSG ratio decreased significantly in response to drought stress. Salt stress led to a significant increases of ascorbate peroxidase (APX), glutathione reductase (GR), glutathione S-transferases (GST) activities; whereas, catalase (CAT) and glyoxalase II (Gly II) activities decreased. Drought stress resulted in a significant increase in monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione peroxidase (GPX) and glyoxalase I (Gly I) activities; whereas, CAT and Gly II activities decreased. Seedlings primed with heat-shock positively modulates the activities of APX, DHAR, GR, GST, GPX, CAT, Gly I and Gly II, and maintained lower levels of GSSG, H2O2 and MDA as compared to the control mostly also salt and drought-stressed seedlings. Our results showed that a retention of the imprint of previous stress exposure (heat-shock) protects the plants from salt and drought-induced oxidative stress by stimulation of antioxidative and glyoxalase defense systems.