Physiological changes in osmotically stressed detached leaves of alfalfa genotypes selected in vitro

In an extensive breeding program based on biotechnological approaches several alfalfa regenerants were selected in vitro for PEG-tolerance. A system in which severe osmotic shock is applied to detached leaves was developed and some physiological traits were followed. No significant differences in relative water content (RWC) decrease, proline accumulation and ion leakage between the tested genotypes were found with 40% PEG stress. When the samples were allowed to recover on osmotic-free buffer clear distinction could be made. The osmotic-tolerant genotypes were able to restore their RWC after 24 h on PEG, while the sensitive plants (the explant-source genotype) lost this capability. The well defined tendency to restore relatively low values of proline content and ion leakage during recovery could be related to osmotic tolerance. Electrophoretic mobility appears to be a sensitive test for assessment of osmotically-induced changes of the cell surface. The surface charge density of the leaf thylakoids in two of our regenerants was not greatly affected by the osmotic stress and they were able to restore their initial values. Further studies with plants from the primarily established regenerants and their progeny, after self-pollination under controlled and field conditions, are in progress, to confirm the correlation between the tolerance to PEG and drought. (C) 1997 Elsevier Science Ireland Ltd.