Ion accumulation in the cell walls of rice plants growing under saline conditions: evidence for the Oertli hypothesis

When plants of rice (Oryza sativa L.) are subjected to mildly saline (50 mol m-3 NaCl) conditions, the leaves show symptoms of water deficit, even though ion accumulation has been more than sufficient to adjust to the decrease in external water potential. After a few days of exposure to salt, there is a negative correlation, in a population of leaves, between the leaf water concentration (g water per g dry weight) and their sodium concentration (mmol Na per g dry weight). Ion concentrations in the cell walls and the cytoplasm of cells of plants grown in low salinity were measured by X-ray microanalysis. The NaCl concentration in solution in the apoplast was calculated to be around 600 mol m-3 in leaves of plants whose roots were exposed to only 50 mol m-3 NaCl. This constitutes strong evidence that an important factor in salt damage in rice is dehydration due to the extracellular accumulation of salt as suggested in the Oertli hypothesis. The implication, that changes in tissue ion concentration and solute potentials equivalent to the external medium is not evidence of plant osmotic adjustment to salinity, is discussed

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