Membrane potential and ph control in the cyanobacterium synechococcus r 2 anacystis nidulans pcc 7942
Journal of Plant Physiology 137(4): 409-418
The membrane potential (.DELTA.psi.i,o) and intracellular pH (pHi) in the cyanobacterium Synechococcus R-2 (Anacystis nidulans) (PCC7942) were measured. .DELTA.psi.i,o was measured using valinomycin-mediated uptake of 86Rb+. .DELTA.psi.i,o under control conditions (BG-11 medium, pHo 7.5, [K+]o 0.35 mol m-3, [Na+]o 18.04 mol m-3) was -126 .+-. 1.2 mV (light) and -115 .+-. 3.1 mV (dark). Anaerobic conditions in the dark did not depolarise .DELTA.psi.i,o any further. DCMU did not depolarise .DELTA.psi.i,o to the value observed in the dark. The following parameters all refer to cells in the light. Nigericin (5 mmol m-3) depolarised .DELTA.psi.i,o to -98 m V and carbonyl cyanide D-trifluoromethoxy phenylhydrazone (FCCP) (5 mmol m-3) to -78 mV; nigericin + FCCP depolarised by more than the two separately (-62 mV). Monensin (100 mmol m-3) depolarised .DELTA.psi.i,o to -90 mV. Synechococcus actively took up K+ at [K+]o below 1 mol m-3 but K+ was in electrochemical equilibrium at higher [K+]o where increasing [K+]o depolarised .DELTA.psi.i,o by 56 .+-. 3 mV/log [K+]o. .DELTA.psi.i,o was insensitive to [Na+]o below 50 mol m-3. EK+i,o and .DELTA.mu.K+i,o were independent of [Na+]o at concentrations below 30 mol m-3. No evidence was found for an interaction between pHo and [K+]i at 0.35 mol m-3 K+o. In neutral and alkaline pHo the .DELTA.psi.i,o was -120 to -130 mV; in acid pHo .DELTA.psi.i,o depolarised to -80 to -90 mV. pHi was measured using [14C]-5,5 dimethyl oxazolidine 2,4 dione (DMO) and [14C]-ethylamine. pHi was very stable; ranging from 7.16 .+-. 0.03 to 7.55 .+-. 0.02 over a pHo range from 5 to 10 in the light. The pmfi,o (proton motive force) progressively fell from -220 .+-. 3 mV at the pHo 5 to + 32 .+-. 6 mV at pHo 10 by 48.9 .+-. 11 mV/pHo. Synechococcus activity extruded H+ at all pHo below 9 but H+ was actively taken up at pHo10.