EFFECT OF WATER-STRESS ON FROST-RESISTANCE OF OAT LEAVES

With the purpose of probing the effects of drought stress on cold resi stance, plants of Az;ena sativa cultivar 'Nehuen' (moderately drought resistant) were subjected to two levels of water stress (-0.5 and -2.0 MPa) for different periods of time. At various intervals over 48 h, w ater and osmotic potentials, membrane permeability, abscisic acid (ABA ), sucrose, proline and glycine betaine contents, and frost resistance of leaves were determined. The frost resistance (LT50) of non-stresse d plants was -3.2 degrees C, and -4.0 degrees C after 6 h at -2.0 MPa. Water and osmotic potential decreased under water stress. Changes in membrane permeability, measured as ion leachate, were detected after 6 h of stress only at the highest level of stress. Proline and sucrose contents increased with stress duration, while glycine betaine increas ed only after 12 h at -2.0 MPa. The basal ABA content was 2.4 mu mol g (-1) dry weight, and remained unchanged during the stress treatments. Unsaturation ratio of fatty acids (unsaturated/saturated) in galactoli pids decreased under water stress, while cold resistance was augmented . The water stress-induced cold resistance in oat leaves correlated on ly with the accumulation of proline and sucrose and not with ABA chang es and fatty acid unsaturation. (C) 1997 Published by Elsevier Science B.V.