Synthetic strigolactone (rac-GR24) alleviates the photosynthetic inhibition and oxidative damage in alfalfa (Medicago sativa L.) under salt stress

Salt stress is one of the main environmental factors affecting plant growth. Photosynthesis, which provides the energy needed for plant growth and development, will be severely restricted under salt stress. Strigolactones (SLs), a class of carotenoid-derived phytohormone, play an important role in regulating plant growth and responding to multiple biotic and abiotic stresses. In this study, we investigated the role of rac-GR24 (a synthetic SLs analog) in the amelioration of salt stress in the photosynthesis of alfalfa. These results showed that rac-GR24 treatment could increase the content of soluble sugar and soluble protein, increase superoxide dismutase, catalase, and peroxidase activity and reduce the content of malondialdehyde in alfalfa leaves, thus relieving the damage caused by salt stress in alfalfa leaves. Moreover, rac-GR24 treatment could also regulate the K⁺/Na⁺ homeostasis, improved stomatal conductance and increased chlorophyll content, which improved the photosynthesis limited by salt stress. The expression levels of selected gene for photosynthesis and antioxidants were consistent with the physiological performance. Our study indicated that rac-GR24 could alleviate the negative effects on photosynthesis of alfalfa under salt stress.