The cyanobacterium synechococcus r 2 anacystis nidulans synechococcus leopoliensis pcc 7942 has a sodium dependent chloride transporter
Ritchie, R.J.
Plant Cell and Environment 15(2): 163-177
1992
ISSN/ISBN: 0140-7791
Accession: 007880725
Synechococcus R-2 (PCC 7942) actively accumulated Cl- in the light and dark, under control conditions (BG-11 media: pHo, 7.5; [Na+]o, 18 mol m-3; [Cl-]o, 0.508 mol m-3). In BG-11 medium [Cl-]i was 17.2 .+-. 0.848 mol m-3 (light), electrochemical potential of Cl- (.DELTA.mu.Cl-i,o) = +211 .+-. 2mV; [Cl-]i = 1.24 .+-. 0.11 mol m-3 (dark), .DELTA.mu.Cl-i,o = +133 .+-. 4 mV. Cl- fluxes, but not permeabilities, were much higher in the light: .phi.Cl-i,o = 4.01 .+-. 5.4 nmol m-2 s-1, PCl-i,o = 47 .+-. 5 pm s-1 (light); .phi.Cl-i,o = 0.395 .+-. 0.071 nmol m-2 s-1, PCl-i,o = 69 .+-. 14 pm s-1 (dark). Chloride fluxes are inhibited by acid pHo (pHo 5; .phi.Cl-i,o = 0.14 .+-. 0.04 nmol m-2 s-1); optimal at pHo 7.5 and not strongly inhibited by alkaline pHo (pHo 10; .phi.Cl-i,o = 1.7 .+-. 0.14 nmol m-2 s-1). A Cl-in/2H+in coporter could not account for the accumulation of Cl- alkaline pHo. Permeability of Cl- is very low, below 100 pm s-1 under all conditions used, and appears to be maximal at pHo 7.5 (50-70 pm s-1) and minimal in acid pHo (20 pm s-1). DCCD (dicyclohexylcarbodiimide) inhibited .phi.Cl-i,o in the light about 75% and [Cl-]i fell to 2.2 .+-. 0.26 (4) mol m-3. Valinomycin had no effect but monensin severely inhibited Cl- uptake ([Cl-]i = 1.02 .+-. 0.32 mol m-3; .phi.Cl-i,o = 0.20 .+-. 0.1 nmol m-2 s-1). Vanadate (200 mmol m-3) accelerated the Cl- flux (.phi.Cl-i,o = 5.28 .+-. 0.64 nmol m-2 s-1) but slightly decreased accumulation of Cl- ([Cl-]i = 13.9 .+-. 1.3 mol m-3) in BG-11 medium but had no significant effect in Na+-free media. DCMU (dichlorophenyldimethylurea) did not reduce [Cl-]i or .phi.Cl-i,o to that found in the dark ([Cl-]i = 8.41 .+-. 0.76 mol m-3; .phi.Cl-i,o = 2.06 .+-. 0.36 nmol m-2 s-1). Synechococcus also actively accumulated Cl- in Na+-free media, [Cl-]i was lower but .DELTA.psi.i,o hyperpolarized in Na+-free media and so the .DELTA.mu.Cl-i,o was little changed ([Cl-]i = 7.98 .+-. 0.698 mol m-3; .DELTA.mu.Cl-i,o = +203 .+-. 3 mV). Net Cl- uptake was stimulated by Na+; Li+ acted as a partial analogue for Na+. Synechococcus has a Na+ activated Cl- transporter which is probably a primary 2Cl-/ATP pump. The Cl- pump is voltage sensitive. .DELTA.mu.Cl-i,o is directly proportional to .DELTA.psi.i,o (P .mchlt. 0.01%): .DELTA.mu.Cl-i,o = -1.487 (.+-. 0.102) .times. .DELTA.psi.i,o, r = -0983, n = 31. The .DELTA.mu.Cl-i,o increased (more positive) as the .DELTA.psi.i,o became more negative. The .DELTA.mu.Cl-i,o has no known function, but might provide a driving force for the uptake of micronutrients.