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The cyanobacterium Synechococcus R‐2 ( Anacystis nidulans, S. leopoliensis ) PCC 7942 has a sodium‐dependent chloride transporter
Author(s) -
RITCHIE R. J.
Publication year - 1992
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1992.tb01470.x
Subject(s) - chemistry , chloride , sodium , synechococcus , nuclear chemistry , medicinal chemistry , stereochemistry , cyanobacteria , bacteria , biology , organic chemistry , genetics
Synechococcus R‐2 (PCC 7942) actively accumulated Cl − in the light and dark, under control conditions (BG‐11 media: pH o , 7·5; [Na + ] o , 18 mol m −3 ; [Cl − ] o , 0·508 molm −3 ). In BG‐11 medium [Cl − ], was 17·2±0·848 mol m −3 (light), electrochemical potential of Cl − (ΔμCl − i,o ) =+211±2mV; [Cl − ] i = 1·24±0·11 mol m −3 (dark), ΔμCl − i,o =+133±4mV. Cl − fluxes, but not permeabilities, were much higher in the light: ϕCl − i,o = 4·01±5·4 nmol m −2 s −1 , P Cl − i,o = 47±5pm s −1 (light); ϕCl − i,o = 0·395±0·071 nmol m −2 s −1 , P Cl − i,o = 69±14 pm s −1 (dark). Chloride fluxes are inhibited by acid pH o (pH o 5; ϕCl − i,o = 0·14±0·04 nmol m −2 s −1 ); optimal at pH o 7·5 and not strongly inhibited by alkaline pH o (pH o 10; ϕCl −1 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 pH o . Permeability of Cl − is very low, below 100pm s −1 under all conditions used, and appears to be maximal at pH o 7·5 (50–70 pm s −1 ) and minimal in acid pH o (20pm s −1 ). DCCD (dicyclohexyl‐carbodiimide) inhibited ϕCl − 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 ; ϕCl − i,o = 0·20±0·1 nmol m −2 s −1 ). Vanadate (200 mmol m −3 ) accelerated the Cl − flux (ϕCl − i,o = 5·28±0·64 nmol m −2 s −1 ) but slightly decreased accumulation of Cl − ([Cl − ], = 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 − ], or ϕCl − i,o to that found in the dark ([Cl − ] i = 8·41±0·76 mol m −3 ; ϕCl − 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 ΔΨ i,o hyperpolarized in Na + ‐free media and so the ΔμCl − i,o was little changed ([Cl − ] i = 7·98±0·698 mol m −3 ; ΔμCl − 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. ΔμCl − i,o is directly proportional to ΔΨ i,o (P»0·01%): ΔμCl − i,o = ‐1·487 (±0·102) ×ΔΨ i,o , r = ‐0·983, n = 31. The ΔμCl − i,o increased (more positive) as the Δμ i,o became more negative. The ΔμCl − i,o has no known function, but might provide a driving force for the uptake of micronutrients.