Nitric oxide and hydrogen peroxide alleviate drought stress in marigold explants and promote its adventitious root development

Drought stress is one of the most important environmental factors that regulates plant growth and development. In this study, we examined the effects of nitric oxide (NO) and hydrogen peroxide (H2O2) on adventitious rooting in marigold (Tagetes erecta L.) under drought stress. The results showed that the promoting effect of NO or H2O2 on rooting under drought stress was dose-dependent, with a maximal biological response at 10 μM NO donor sodium nitroprusside (SNP) or 600 μM H2O2. Results also indicated that endogenous NO and H2O2 may play crucial roles in rooting under drought conditions, and H2O2 may be involved in rooting promoted by NO under drought stress. NO or H2O2 treatment attenuated the destruction of mesophyll cells ultrastructure by drought stress. Similarly, NO or H2O2 increased leaf chlorophyll content, chlorophyll fluorescence parameters (Fv/Fm, ΦPS II and qP), and hypocotyls soluble carbohydrate and protein content, while decreasing starch content. Results suggest that the protection of mesophyll cells ultrastructure by NO or H2O2 under drought conditions improves the photosynthetic performance of leaves and alleviates the negative effects of drought on carbohydrate and nitrogen accumulation in explants, thereby adventitious rooting being promoted.