Safflower (Carthamus tinctorius) Biochemical Properties, Yield, and Oil Content Affected by 24-Epibrassinosteroid and Genotype under Drought Stress.

The steroid hormones, including brassinosteroids, regulate plant growth under stress. It is hypothesized that 24-epibrassinosteroids (24-EBR) can affect safflower (Carthamus tinctorius) biochemical properties, crop yield, and oil content under drought stress. The objective of our study was to determine the response of three safflower genotypes (Goldasht, Faraman, and Sina) to exogenous 24-EBR (0 and 10-7 M) under drought stress, including 85, 65, and 45% of field capacity in 2015. Stress decreased chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid, relative water content (RWC), seed yield, and oil percentage. The activities of superoxide dismutase (SOD), catalase (CAT), polyphenol oxidase (PPO), and proline contents increased in response to either drought stress or 24-EBR. Genotypes behaved significantly different under stress. 24-EBR significantly increased plant chlorophyll contents and oil percentage, and it significantly reduced the malondialdehyde (MDA) content via increasing the proline and carotenoid contents under stress. 24-EBR can increase safflower oil and seed yield under drought stress.