The Apparent Induction of Nitrate Uptake byChara corallinaCells following Pretreatment with or without Nitrate and Chlorate

Nitrate provision has been found to regulate the capacity for Chara corallina cells to take up nitrate. When nitrate was supplied to N sufficient cells maximum nitrate uptake was reached after 8 h. Prolonged treatment of the cells in the absence of N also resulted in the apparent ability of these cells to take up nitrate. Chlorate was found to substitute partially for nitrate in the ‘induction’ step. The effects on nitrate reduction were separated from those on nitrate uptake by experiments using tungstate. Tungstate pretreatment had no effect on NO−3 uptake ‘induced’ by N starvation, but inhibited NO−3 uptake associated with NO−3 pretreatment. Chloride pretreatment similarly had no effect on NO−3 uptake ‘induced’ by N deprivation, but inhibited NO−3 uptake following NO−3 pretreatment. The data suggest that there are at least two mechanisms responsible for the ‘induction’ of nitrate uptake by Chara cells, one associated with NO−3 reduction and ‘induced’ by CIO−3 or NO−3 and one associated with N deprivation.