Salt Stress and Comparative Physiology in the Gramineae. II. Glycinebetaine and Proline Accumulation in Two Salt- and Water-Stressed Barley Cultivars

Under low-salt conditions, the glycinebetaine levels in the shoot exceeded the proline levels in two barley cultivars, California Mariout and Arimar. Stress induced by both polytheylene glycol (PEG) and NaCl caused an accumulation of both compounds. However, a gradual incremental increase in stress led to higher glycinebetaine than proline levels, whereas salt and osmotic shock led to proline levels far in excess of the glycinebetaine levels. Both stress regimes caused a greater proportional increase in proline than in glycinebetaine. Preliminary data suggest that proline may be used as an internal assay for water stress in barley leaves. Comparison of the physiological responses of the barley cultivars to NaCl and PEG stress suggested that the suppression of growth by salt treatment was not due directly to the low external water potential but arose either from the ions, Na+ and Cl-, interfering with metabolic processes or from a number of possible but unsubstantiated interactions leading to a reduction in turgor potential and thus in the rate of cell expansion.