Effect of Osmotic Stress Upon Endogenous Hormone Levels in Euphorbia lathyrus L. and Vicis faba L.

Ethylene concentrations rise in stems, lacunae and roots of Euphorbia Iathyrus subjected to osmotic stress. In contrast to other species, however, no such changes are observed in leaves. Similarly, ABA concentrations rise in the leaves of osmotically-stressed plants but little change was observed in roots. In no case was there any strong evidence for the existence of a threshold of osmotic potential above which a response will not occur. Instead, marked increases in concentrations of both ABA and ethylene were obtained in response to osmotic stresses which did not result in significant changes in water saturation defecit (WSD) during the experiment. In Vicia faba, time course studies at constant osmotic potential showed that ABA concentrations increased with duration of stress and increased WSD but the effect was most marked in younger tissues for a given level of stress. Concentrations of bound ABA showed a similar pattern with time but here the change was least marked in the younger tissues.