Effect of Abscisic Acid on Glucose Metabolism in Guard Cells of Vicia faba L.

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The effects of abscisic acid (ABA) on the formation of osmotically active solutes and on cell-wall synthesis in guard cells were examined using sonicated abaxial epidermal strips of Vicia faba L. incubated with ^<14>C-glucose at pH 4 and 6. Radioactivity was incorporated mainly into malate, sucrose, starch and cell-wall fractions. ^<14>C-Glucose uptake by the guard cells was reduced when 1μM ABA was added. Malate formation, which was more active at pH 6 than at 4, was inhibited by ABA at pH 6, but not at pH 4. Conversion of ^<14>C-glucose into ^<14>C-sucrose was stimulated by ABA at both pH values. Release of radioactive solutes (composed mainly of glucose and malate) from the guard cells into the medium was more active at pH 6 than at pH 4. ABA stimulated the release at both pH values. Turnover of starch was more remarkable when the pH value was 6. ABA inhibited the synthesis of starch, but did not affect its degradation. Cell-wall synthesis in the guard cells was also inhibited by ABA, the inhibition rate being greater at pH 4 than at pH 6. These results suggest that ABA may have two different actions on stomatal movement: to change the metabolic activities in the guard cells so as to lower the concentration of osmotically active solutes, and to change the mechanical properties of cell walls by modulating cell-wall metabolism.
日本植物生理学会の論文