Sulfate Uptake inArabidopsis thaliana

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Abstract
Sulfate uptake of Arabidopsis thaliana seedlings were characterized. Sulfate uptake obeyed single Michaelis‐Menten's kinetics. When plants were grown in the medium containing 1,500 mM sulfate (control), Km was 20.0±3.60 mM and the Vmax ranged from 21 to 54 nmol g‐1 fresh weight hr‐1. While Km of plants grown in the sulfate‐deficient (‐S) medium containing 10 mM sulfate was not significantly changed, Vmax of plants grown in the ‐S medium increased by two fold. In the presence of selenate, an analogue to sulfate, Vmax remained unchanged, indicating that selenate is a competitive inhibitor for sulfate uptake. Metabolic inhibitors and high pH decreased sulfate uptake, suggesting that sulfate uptake system requires a H+ gradient generated by a H+‐ATPase. Transfer of seedlings from the control to the ‐S medium increased the rate of sulfate uptake and vice versa, suggesting that sulfate uptake in A. thaliana was regulated by external sulfate concentrations. These characteristics of sulfate uptake in A. thaliana are similar to those reported for other plant species.