Effect of Exogenous Application of 24-Epibrassinosteroids and Hydrogen Peroxide on Some Biochemical Characteristics of Cuminum cyminum L. grown under Drought Stress

To evaluate the responses of cumin plant to different levels of drought stress with exogenous application of either 24-epibrassinolide (24-EBL) or hydrogen peroxide (H2O2) and a mixture of them, a factorial experiment was conducted, in a complete randomized design with three replicas, at the experimental greenhouse. Treatments included three levels of drought stress (100%, 75%, and 50% of FC) in which at fifth week after germination (beginning of reproductive growth) application of H2O2 (0, 0.5 and 1mM) and 24-epibrassinosteroid (0, 0.5 and 1mM) at two stages, first 3 days before applying the then, 15 days after. The results showed that with increasing stress intensity, the amounts of proline, malondialdehyde and superoxide dismutase (SOD) enzyme increased, but decreased the total protein and catalase enzyme in the root. The results of interaction between drought stress and exogenous application of 24-EBL showed the highest total protein content (11.30 mg/l) at 1mM 24-EBL under moderate stress of 75% of FC. Also, the highest of proline content of the root and shoot were obtained (10.15 and 10.91 mMol gFW–l, respectively) under severe stress (50% FC) and spraying with 1mM 24-EBL, respectively. However, a decrease in MDA content, with the application of 24-EBL e and H2O2, was recorded. In general, it can report that drought stress reduced the efficiency of photosynthesis and plant production. Moreover, application of 24-EBL and H2O2 was able to improve the photosynthetic system and resistance of the cumin plant to stress.