Photosynthetic oxygen evolution in relation to ion contents in the chloroplasts of Suaeda maritima

The effects of sodium chloride on photosynthetic oxygen evolution by chloroplasts isolated from the leaves of the halophyte Suaeda maritima L. (Dum) are reported. When plants were grown in concentrations of salt increasing to 340 mol m-3 the rate of oxygen evolution by isolated chloro-plasts increased; beyond this concentration of salt it declined. Maximum rates of oxygen evolution (coupled and uncoupled) were found when the plants were grown in 340 mol m-3 NaCl. Under these conditions mean ion concentrations in the chloroplasts measured in vivo by X-ray microanalysis were Na+, 84–257 mol m-3; Cl-, 86–212 mol m-3; K+, 23–36 mol m-3. A comparative study was also made of the in vitro effects of sodium chloride on oxygen evolution. Here again maximum rates were found in the presence of 340 mol m-3 NaCl.