Salt Stress and Comparative Physiology in the Gramineae. III. Effect of Salinity Upon Ion Relations and Glycinebetaine and Proline Levels in Spartina × townsendii

S. × townsendii was grown at a number of salinity levels ranging from 0 to 800 mol m-3. Growth was suppressed by all salt treatments, but in particular, above 300-400 mol m-3. The osmotic pressure of the extracted shoot sap paralleled the rise in the osmotic pressure of the medium. Osmotic compensation was attributed to Na+ and Cl- accumulation at low salinities and to a lowered fresh weight : dry weight ratio at the higher salinities. In the shoots sf plants grown in 50-100 mol m-3 NaCl, Na+ accumulation exceeded the K+ decline. Root K+ was unaffected by all salt treatments. The shoot glycinebetaine content rose in response to external salinity and the accumulation of glycinebetaine was highly correlated (r = 0.99; P < 0.01) with the increase in sap osmotic pressure. Proline also accumulated in response to salt stress and was correlated with sap osmotic pressure (r = 0.98; P < 0.01). However, proline levels were much lower than those of glycinebetaine and became quantitatively significant only in shoots exposed to high inhibitory salinities.