Effect of high and low sulfate concentrations on adenosine 5′‐phosphosulfate sulfotransferase activity from Lemna minor

The effect of Na2SO4 concentrations from 0 to 17.6 mM in the nutrient solution of Lemna minor L. strain 6580 on adenosine 5′‐phosphosulfate sulfotransferase activity was examined. Routinely, the plants were cultivated on 0.88 mA SO42−. The enzyme activity was increased by 50 to 100% after transfer to 0 or 0.0088 mM SO42−. Transfer back to 0.88 mM rapidly decreased the enzyme activity to the initial level. Cultivation on 17.6 mM Na2SO4 redueed extractable adenosine 5′‐phosphosulfate sulfotransferase by 50%. The original level was rapidly re‐established on 0,88 mM. In control experiments, a decrease in adenosine 5′‐phosphosulfate sulfotransferase activity was also induced by K2 SO4, whereas NaCl caused a small increase. This indicates that the observed effects are dependent on the sulfate ion. ATP‐sulfurylase activity measured for comparison was only significantly affected by the omission of sulfate, which induced a 20% increase, indicating that this enzyme activity from Lemna minor is less suseeptible to changes in medium sulfate than adenosine 5′‐phosphosulfate sulfotransferase. A close relationship between adenosine 5′‐phosphosulfate sulfotransferase activity and the content of asparagine, glutamine, non‐protein thiols and sulfate in the tissue was detected, indicating a positive control mechanism induced by amides and a negative mechanism induced by thiols and sulfate.