[Correlation of the uptake of nitrate, nitrite and phosphate to the photosynthetic reduction of nitrate and nitrite and to the ATP-level in Ankistrodesmus braunii].

The pH-dependence of NO 3 (-) and NO 2 (-) uptake is different from that of phosphate uptake, but similar to that of sulfate uptake, with optima between pH 7.4 and 8.2 and smaller peaks at higher H(+)-concentration.Since the ATP-level is not affected by addition of ions and since phosphate uptake is not depressed by NO 3 (-) , the inhibition of phosphate uptake by K(+) reported in former papers cannot be explained by competition for the available energy(ATP) at the site of uptake.NO 3 (-) uptake is strongly dependent on the activity of the NO 3 (-) reducting system, as can be seen from the inhibition of NO 3 (-) uptake in light by N2 compared with that in air. Furthermore, the pH-dependences of NO 3 (-) and NO 2 (-) uptake correspond to the pH-optima known for the reductases.Phosphate uptake is enhanced by NO 3 (-) and NO 2 (-) in N2. Since the enhancement of phosphate uptake is sensitive to DCMU and since this DCMU-sensitive phosphate uptake is accompanied by O2-evolution, it is probably due to an NO 3 (-) -stimulated noncyclic photophosphorylation which enhances the ATP-turnover and hence the incorporation of phosphate into organic compounds.