Phosphate alleviates arsenate toxicity by altering expression of phosphate transporters in the tolerant barley genotypes

The contribution of the phosphate transporters (PHTs) in uptake of arsenate (As5+) and phosphate (P) is a widely recognized mechanism. Here we investigated how P regulates the uptake of As5+ and the subsequent effects on growth and relative expression of PHTs. The study was conducted on 3 barley genotypes differing in As tolerance (ZDB160, As-tolerant; ZDB115, moderately tolerant; ZDB475, As-sensitive) using a hydroponic experiment. There were 3 As5+ (0, 10 and 100 mu M) and 3 P (0, 50 and 500 mu M) levels. The results showed that the negative effect of As stress on plant growth, photosynthesis and cell ultra-structure is As dose and barley genotype dependent, confirming the distinctly genotypic difference in As tolerance. As uptake and accumulation in plant tissues are closely associated with inhibited extent of growth and photosynthesis, with the tolerant genotype ZDB160 having lower As content than other two genotypes. The toxic effect caused by As stress could be alleviated by P addition, mainly due to reduced As uptake. Moreover, the tolerant genotype showed relatively lower expression PHT5 than sensitive ones upon exposure to both As stress and P addition, suggesting regulation of PHT5 expression is a major mechanism for relative uptake of As and P, in subsequence affecting As tolerance. Moreover, among 6 PHTs examined in this study, the expressions of PHT1.3, PHT1.4 and PHT1.6 showed the marked difference among the three barley genotypes in responses to As stress and P addition, indicating further research on the contribution of phosphate transporters to As and P uptake should be focused on these PHTs.