Effect of Exogenous Sulfur on Photosynthesis System of Fagopyrum tataricum Seedlings Under Cadmium Stress

This study explored the physiological mechanism of adscititious sulfur induced cadmium tolerance in tartary buckwheat (Fagopyrum tataricum) on the photosynthetic reaction system. The results showed that the supplementation of S could boost chlorophyll a and b content during Cd treatment, as well as the chlorophyll a/b ratio. Cd stress significantly increased the contents of ALA, PBG, Urogen III, Coprogen III, and Proto IX, while the Mg-Proto IX and pchlide contents were significantly reduced. These results indicate that Cd stress block the synthesis of chlorophyll through interruption of the synthesis of Mg-Proto IX. The adoption of additional S under Cd stress reversed the above contents to the control level. In addition, Cd stress had no significant effect on iron and calcium content, yet was able to significantly decrease Mg, Mn, and Cu content. The lack of Cu and Mn in the tartary buckwheat leaves consequently resulted in the interruption of the electron transport chain at the oxidation region of the PSII reaction centers. The photosynthesis and quantum yield of the PSII photochemistry were both significantly enhanced with additional sulfur under Cd treatment. In conclusion, the results advance the theoretical mechanism of excess S in alleviating the Cd stress in plants through the photosynthetic pathway.