Effects of Rapidly and Slowly Permeating Osmotica on Metabolism

Zea mays was exposed to solutions of low water potentials by addition of ethylene glycol or mannitol. Intact seedlings were treated for 1 hr at potentials between -10 and -20 atmospheres and then returned to high water potentials. Subsequent root extension was slow after mannitol treatment, but rapid when ethylene glycol had been used as the osmoticum. Cellular activity of excised roots was also affected much less by ethylene glycol than by mannitol. Processes studied included respiration, glucose uptake, and synthesis of methanol-insoluble compounds. These differences in response to various osmotica applied both during and after treatment at low water potentials.Ethylene glycol penetrated the tissues much more rapidly than mannitol. Rapid penetration of the osmoticum would minimize turgor loss and plasmolysis. Thus, the data suggest that adverse effects were induced by water loss or structural changes, or both, during plasmolysis, rather than by low water potentials, demonstrating the crucial importance of osmotic adjustment.