The relationship between phosphate status and photosynthesis in leaves : Reversibility of the effects of phosphate deficiency on photosynthesis.

Spinach (Spinacia oleracea L.) and barley (Hordeum vulgare L.) were grown in hydroponic culture with varying levels of orthophosphate (Pi). When leaves were fed with 20 mmol·l(-1) Pi at low CO2 concentrations, a temporary increase of CO2 uptake was observed in Pi-deficient leaves but not in those from plants grown at 1 mmol·l(-1) Pi. At high concentrations of CO2 (at 21% or 2% O2) the Pi-induced stimulation of CO2 uptake was pronounced in the Pi-deficient leaves. The contents of phosphorylated metabolites in the leaves decreased as a result of Pi deficiency but were restored by Pi feeding. These results demonstrate that there is an appreciable capacity for rapid Pi uptake by leaf mesophyll cells and show that the effects of long-term phosphate deficiency on photosynthesis may be reversed (at least temporarily) within minutes by feeding with Pi.