Exogenous Application of Salicylic Acid and Chlormequat Chloride Alleviates Negative Effects of Drought Stress in Wheat

Many plant growth regulators (PGRs) are known to alleviate the negative effects of drought stress in plants. However, limited research has been conducted to investigate the potential benefits of exogenous application of PGRs in wheat plants grown under drought stress. In the present study, effects of salicylic acid (SA) and chlormequat chloride (CCC) on drought-stress induced changes in morpho-physiological and biochemical characteristics of two commonly grown wheat cultivars in Iran were assessed. Plants were field grown under three water regimes, non-stress (normal 502 H. Pirasteh Anosheh, Y. Emam, M. Ashraf and M. R. Foolad irrigation), moderate drought stress (water withheld from flowering stage to season end), and severe drought stress (water withheld from double ridges stage to season end), and two foliar applications of PGRs, SA (0.7 mM) and CCC (2.5 g/l). Drought stress increased canopy temperature and decreased leaf area index and plant height in both cultivars, however, exogenous applications of PGRs reduced these harmful effects considerably. Drought stress also significantly increased the levels of total soluble proteins and free proline, the activities of antioxidant enzymes superoxide dismutase, peroxidase and catalase, and decreased the contents of chlorophyll a and chlorophyll b. Application of CCC significantly increased all measured parameters except total soluble proteins and application of SA increased total soluble proteins, chlorophylls a and b, and peroxidase activity. These observations indicated that both SA and CCC were effective in alleviating adverse effects of drought stress in wheat, though the responses of the two wheat cultivars were not always the same. The beneficial effects of SA and CCC in reducing the adverse effects of drought stress may be due to improving stomatal regulation, maintaining leaf chlorophyll content, increasing water use efficiency, and stimulating root growth.