| Abstract: | The relationships between changes in WSD,2 stomatal resistance,and hormone levels during stress and stress recovery have beeninvestigated in a perennial plant, Populus robusta, over anextended stress period, involving a number of stress cyclesof differing duration. There were marked increases in WSD, stomatal resistance, freeABA levels, and ethylene levels in leaves and stems during stressimposition. However, during stress recovery, WSD declined mostrapidly, while decreases in other parameters were related tothe duration of the preceding stress. In general, the declinein stomatal resistance and free ABA levels to control valueswas protracted. Although there were increases in bound ABA levels,above control values, there was no close correlation with changesin free ABA levels. The concentrations of bound ABA observedin the latter phases of these experiments were higher than freelevels. No clear pattern of change in IAA concentration emerged in responseto stress or stress recovery. Although ethylene concentrations rise in response to initialstress imposition and fall during relief, subsequent stressand stress relief periods were without significant effect. The results are discussed in relation to the role of endogenousgrowth regulators in the response of plants to stress and inparticular the fate of stress-induced ABA. |
