Difference in selenite absorption between high- and low-selenium rice cultivars and its mechanism

Two rice cultivars, Xiushui 48 and S. Andrea, with significant difference in selenium (Se) concentrations in brown rice grains, were chosen to study the Se absorption and its mechanism in excised roots. The results showed that the high-selenium cultivar Xiushui 48 absorbed higher amounts of Na2SeO3 than low-selenium S. Andrea at different Se levels and treatment periods. It was found that Na2SO3 markedly inhibited Na2SeO3 absorption by the excised roots of both cultivars. This inhibition might be due to the competition for uptake on the fact that Na2SO3 might share a common uptake pathway with Na2SeO3. Treatment with ZnCl2 significantly decreased Na2SeO3 absorption of both cultivars possibly by inhibiting the activity of cysteine synthase. It was therefore postulated that the difference in cysteine synthase activity might be one of the reasons which resulted in difference in selenite absorption possibly between the two cultivars. Both HgCl2 and AgNO3 treatments can inhibit selenite absorption by rice roots greatly. We propose that selenite enters rice roots through aquaporins as the form of H2SeO3.