Effects of slowly permeating osmotica on metabolism of vacuolated and nonvacuolated tissues

Abstract

Vacuolated and nonvacuolated root tissues of Zea mays were exposed to low water potentials by addition of mannitol or glycerol. Temporary increases were observed for O(2) uptake, but CO(2) evolution remained steady. This increase in O(2) uptake ceased after 15 minutes. Further treatment induced decreases in respiration, with similar reductions in O(2) uptake and CO(2) evolution.Removal of osmotica from nonvacuolated tissues restored high rates of respiration, uptake of glucose, and synthesis of methanol-insoluble compounds. In contrast, rates of all these processes decreased to very low values when vacuolated tissues were returned to high water potentials. Deplasmolysis also induced rapid leakage of metabolic intermediates from vacuolated tissues, but leakage from nonvacuolated tissues was only slightly increased. It is suggested that these contrasting responses of vacuolated and nonvacuolated tissues are related to differences in structural changes, during either plasmolysis or deplasmolysis.