Improving photosynthesis and the ascorbate-glutathione cycle of own-root and grafted-root chrysanthemums by brassinolide under drought stress

Many studies have demonstrated that brassinolide improves the drought tolerance of plants. This study aims to test whether the drought tolerance of chrysanthemums can be improved by brassinolide and to clarify the underlying physiological mechanism. An own-root chrysanthemum and a corresponding grafted-root line (Artemisia annua rootstock) were treated with brassinolide under three water levels in a randomised complete block design with five replications. The results showed that brassinolide increased the relative water content, net photosynthetic rate, chlorophyll (Chl) fluorescence parameters, Rubisco, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase and monodehydroascorbate reductase activities, ascorbate/dehydroascor-bate, glutathione/oxidised glutathione and dry mass, and reduced the H2O2 content in the own-root and grafted-root chrysanthemums, especially under drought stresses. The magnitude of the changes to the parameters was greater in the own-root line than in the corresponding grafted-root line under brassinolide treatment. The above param-eters showed significant differences (P < 0.05) between the brassinolide chrysanthemums and the corresponding non-brassinolide chrysanthemums under drought stresses. This might be the physiological mechanism of improved drought tolerance by brassinolide in chrysanthemums.