Effects of exogenous salicylic acid on the physiological characteristics of Dendrobium officinale under chilling stress

We investigated the effects of exogenous salicylic acid (SA) on a new variety of Dendrobium officinale seedlings named "ZD-1" under chilling stress and recovery growth. Changes in photosynthetic parameters, PSII key component D1 protein, and antioxidant enzyme activities were determined. Our results indicated that a foliar spray of SA alleviated the decline in the chlorophyll content and increased the malondialdehyde content in D. officinale seedling leaves under chilling stress. The change in the ascorbic acid content, while complex, was understandable. The chilling stress resulted in a decrease in the maximal photochemical efficiency; however, the effect could be removed using exogenous SA. We found significant increases in the net photosynthetic rates of the seedling leaves in plants receiving SA treatments during the chilling stress compared with the control. There were no significant differences in the composition of thylakoid membrane proteins among different treatment groups. However, the western blot analysis showed an increase in the D1 protein content as SA concentrations increased. Approximately 1.5 mmol/L SA had the best effect against stress. SA significantly increased the superoxide dismutase activity and reduced the ascorbate peroxidase and catalase activities during recovery growth after chilling stress. During the recovery period, the maximal photochemical efficiency and net photosynthetic rate of plants receiving SA increased significantly in contrast to the control. These results suggested that the application of SA protected the chloroplast membrane and D1 protein, and enhanced the antioxidant capacity of the plants, which may be beneficial to the recovery growth of D. officinale seedlings.