Sodium-Stimulation of Phosphate Uptake in the Cyanobacterium Anabaena PCC 7119

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Anabaena PCC 7119 showed higher rates of phosphate uptake when cells were under P-star-vation. Phosphate uptake was energy-dependent as indicated the decrease observed when assays were performed in the dark or in the presence of inhibitors of photosynthetic electron transport, energy transfer and adenosine triphosphatase activity. Phosphate uptake was stimulated by Na^+ both in P-sufficient cells and P-starved cells. Li^+ and K^+ acted as partial analogues for Na^+ . The Na^+_stimulation of phosphate uptake followed Michaelis-Menten kinetics, half-saturation (K_<1/2>) of phosphate uptake was reached with a Na^+ concentration of 212 μM. The absence of Na^+ reduced the rates of phosphate uptake at all phosphate concentrations assayed (1-20 μM). The maximum uptake rates (V_<max>) decreased from 658 nmol P (mg dry wt)^<-1> h^<-1> in the presence of Na^+ to 149 nmol P (mg dry wt)^<-1> h^<-1> in the absence of Na^+ . The absence of Na^+ did not change significantly the concentration of phosphate required to reach half-saturation (K_<1/2>) (3.01 μM in the presence of Na^+ vs 3.21 μM in the absence of Na^+). In the presence of Na^+ the rate of phosphate uptake was affected by the pH; optimal rates were observed at pH 8. In the absence of Na^+ phosphate uptake was not affected by the pH; low rates were observed in all cases. Monensin, an ionophore which collapses Na^+_gradients, reduced the rate of phosphate uptake in Na^+_supplemented cells. These results indicated the existence of a Na^+_dependent phosphate uptake in Anabaena PCC 7119.
日本植物生理学会の論文

Sodium-Stimulation of Phosphate Uptake in the Cyanobacterium Anabaena PCC 7119

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