Sulfur dioxide improves drought tolerance through activating Ca signaling pathways in wheat seedlings.

Sulfur dioxide (SO) and drought are two important co-occurring abiotic stresses affecting the growth and productivity of plants. Here, we will investigate the role of Ca in regulating antioxidant defense during drought or SO/drought stress, and the effect of SO pretreatment on the physiological response of wheat seedlings to drought stress. The results showed that exogenous Ca increased the activities of SOD, CAT and POD, and reduced the contents of HO and MDA in drought-treated wheat seedlings, suggesting Ca could improve drought tolerance by promoting antioxidant defense in plants. Moreover, exogenous Ca up-regulated the expression of two stress-responsive transcription factor (TF) genes, ERF1 and MYB30, to cope with drought stress. Exposure of wheat seedlings to 10 mg m SO significantly enhanced the activities of SOD, CAT and POD. The contents of HO and MDA remained at control levels, showing that SO at this concentration led to an activation of the antioxidant defense system and did not cause oxidative damage to the seedlings. Furthermore, 10 mg m SO pretreatment increased the expression of CCaMK and CPK10, enhanced the activities of SOD and POD, and reduced the accumulation of HO and MDA in drought-treated wheat seedlings, showing a role of SO in protection of plants against drought stress. However, with removal of Ca by spraying EGTA on the SO-pretreated wheat seedlings, the expression of transcription factor genes and activities of antioxidant enzymes were decreased, and the contents of HO and MDA enhanced to the level of drought treatment alone, suggesting a role of Ca in the SO-induced alleviation of drought stress. Together, these results indicated that exogenous Ca increased defense-related gene expression and enzyme activity in response to drought stress, and that pre-exposure to appropriate levels of SO could improve drought tolerance through activation of Ca signaling pathways in plants. This study would provide new strategy for enhancing plant resistance to environmental stress.