Beziehungen der Aufnahme von Nitrat, Nitrit und Phosphat zur photosynthetischen Reduktion von Nitrat und Nitrit und zum ATP-Spiegel bei Ankistrodesmus braunii
Planta 115(1): 25-36
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.