Abscisic Acid Accumulation in Spinach Leaf Slices in the Presence of Penetrating and Nonpenetrating Solutes

Publisher Website
Google Scholar
Abstract
Abscisic acid (ABA) accumulated in detached, wilted leaves of spinach and reached a maximum level within 3-4 h. The increase in ABA over that found in detached turgid leaves was .apprx. 10-fold. The effects of water stress could be mimicked by the use of thin slices of spinach leaves incubated in the presence of 0.6 M mannitol, a compound which causes plasmolysis (loss of turgor). About equal amounts of ABA were found both in the leaf slices and in detached leaves, whereas 2-4 times more ABA accumulated in the medium than in the slices. When spinach leaf slices were incubated with ethylene glycol, a compound which rapidly penetrates the cell membrane causing a decrease in the osmotic potential of the tissue and only transient loss of turgor, no ABA accumulated. Ethylene glycol was not inhibitory with respect to ABA accumulation. Spinach leaf slices incubated in both ethylene glycol and mannitol had ABA levels similar to those found when slices were incubated with mannitol alone. Increases similar to those found with mannitol also occurred when Aquacide III, a highly purified form of polyethylene glycol, was used. Aquacide III causes cytorrhysis, a situation similar to that found in wilted leaves. Loss of turgor appears essential for ABA accumulation. When spinach leaf slices were incubated with solutes which are supposed to disturb membrane integrity (KHSO3, 2-propanol or KCl) no increase in ABA was observed. With respect to the accumulation of ABA, mannitol caused a physical stress (loss of turgor) rather than a chemical stress (membrane damage).