Abstract
SULTR1;1 and SULTR1;2 encode high-affinity sulfate transporters co-localizing at epidermis and cortex of Arabidopsis roots. The mRNA levels of both SULTR1;1 and SULTR1;2 increased under sulfur limitation, although SULTR1;2 was more abundant than SULTR1;1. The double mutant, sultr1;1 sultr1;2, failed to absorb sulfate from μM concentration, causing severe growth defects. When grown under high-sulfate condition, only the sulfate uptake of sultr1;2 was significantly impaired. In contrast, the sulfate uptake rate decreased in both sultr1;1 and sultr1;2 under low-sulfate conditions. Sulfate uptake rates in sultr1;1 and sultr1;2 were approximately 60 and 25 % of wild-type, respectively. Contribution of SULTR1;1 and SULTR1;2 to the total sulfate uptake was calculated from the sum of sulfate uptake rates in sultr1;1 and sultr1;2 mutants. However, the estimated capacity was lower than that measured in wild-type. It is suggested that co-expression of SULTR1;1 and SULTR1;2 during sulfur limitation may synergistically facilitate the acquisition of sulfate.
