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 (G _mc) and wild (G _sw) 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 G _sw leaves than those in the G _mc leaves. The observed increases in the Na⁺ concentration in the G _sw leaves were likely responsible for the severe decrease in the photosynthetic activity of grafted plants. We suggest that Na⁺ accumulation in G _sw 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.