Effect of Fusicoccin on Dark 14CO2 Fixation by Vicia faba Guard Cell Protoplasts

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Abstract
When Vicia faba guard cell protoplasts were treated with fusicoccin, dark 14CO2 fixation rates increased by as much as 8-fold. Rate increase was saturated with less than 1 micromolar fusicoccin. Even after 6 minutes of dark 14CO2 fixation, more than 95% of the incorporated radioactivity was in stable products derived from carboxylation of phosphoenolpyruvate (about 50% and 30% in malate and aspartate, respectively). The relative distribution of 14C among products and in the C-4 position of malate (initially more than 90% of [14C]malate) was independent of fusicoccin concentration. After incubation in the dark, malate content was higher in protoplasts treated with fusicoccin. A positive correlation was observed between the amounts of 14CO2 fixed and malate content.