Effect of phosphate and silicate on selenite uptake and phloem-mediated transport in tomato (Solanum lycoperskum L)

摘要

The ambiguous mechanism that selenite seems to be absorbed by roots via phosphorus (P) and silicon (Si) transporters signifies P and Si may affect selenite uptake. However, the role of P and Si in phloem-mediated selenium (Se) transport within plant tissue is unknown. Therefore, in this work, tomato (Soianum lycoperskum L.) seedlings were exposed to selenite under different hydroponic conditions firstly. And then, split-root experiments were conducted. Results showed that Se uptake decreased as external pH increased. At pH 8, more selenite in the form of SeO_3~(2-)~ was assimilated under P-deficient conditions than under P-normal conditions. Silicate inhibited Se uptake only at pH 3 (27.5% H_2SeO_3 +72.5% HSeO_3"). The lesults of split-root experiments showed that Se concentrations in seedlings increased under heterogeneously high P or Si. Selenium transport from shoots to roots immersed in solution without selenite was also enhanced. This study illustrated that me affinity of tomato roots to assimilate selenite species followed the order of H_2SeO_3 >HSeO_3~ >SeO_3~(2-). H_2SeO_3 was absorbed into roots via Si transporters, whereas HSeO_3~(2-) and a portion of SeO_32- were absorbed via low- and high-affinity P transporters, respectively. In addition, heterogeneously high P or Si concentrations in environmental media could enhance phloem-mediated Se redistribution.