Systematic salt tolerance-related physiological mechanisms of wild soybean and their role in the photosynthetic activity and Na+ distribution of grafted soybean plants

Systematic salt tolerance-related physiological mechanisms in roots and shoots of halophyte Dongying wild soybean have not yet been thoroughly studied. In this study, photosynthesis, modulated 820-nm reflection, chlorophyll a fluorescence, and Na+ distribution in cultivated (Gmc) and wild (Gsw) soybean leaves of grafted soybean plants were investigated after NaCl treatment. Results showed that the decreases in photosynthetic rate, performance index, active P700 content, and plastocyanin reduction were significantly greater in the Gsw leaves than those in the Gmc leaves. The observed increases in the Na+ concentration in the Gsw leaves were likely responsible for the severe decrease in the photosynthetic activity of grafted plants. We suggest that Na+ accumulation in Gsw roots, which prevents the transport of Na+ from the roots to the shoots, effectively maintains the concentration of Na+ at a comparatively low level in the leaves to prevent the destruction of the photosynthetic apparatus by salt.