The Regulation of the Starch-Malate Balances during Volume Changes of Guard Cell Protoplasts

Abstract

The enzymatic activities of phosphoenolpyruvate carboxylase (EC 4.1.1.31), ‘malic enzyme’ (EC 1.1.1.40), phosphofmctokinase (EC 2.7.1.11) and fructosebisphosphatase (EC 3.1.3.11) were measured during the swelling and shrinking of isolated and purified guard cell protoplasts (Vicia faba) in darkness. The volume increase was accompanied by the activation of phosphofructokinase and a short stimulation of phosphoenolpyruvate carboxylase, at the same time the ‘malic enzyme’ and fructosebisphosphatase were inhibited. However, during the shrinkage of guard cell protoplasts these two enzymes were activated in contrast to phosphoenolpyruvate carboxylase and phospho-fructokinase. Because of the dramatic increase of phosphoenolpyruvate carboxylase activity during the swelling, this enzyme was assumed to act as a trigger for the swelling phase.