Intracellular Sites of Synthesis and Storage of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid in Acer pseudoplatanus Cells

Vacuoles were isolated from Acer pseudoplatanus cells that were incubated with ¹⁴C]1-aminocyclopropane-1-carboxylic acid (ACC). The kinetics of ¹⁴C]1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) formation are consistent with the interpretation that MACC is synthesized in the cytosol, transported through the tonoplast, and accumulated in the vacuole. Twenty hours after chasing the labeled ACC with unlabeled ACC and adding 1 millimolar unlabeled MACC, all the ¹⁴C]MACC synthesized is located in the vacuole. Whole cells preloaded with ¹⁴C]MACC and then submitted to a continuous washing out, readily release their cytosolic MACC until complete exhaustion. The half-time of MACC efflux from the cytosol, calculated by the technique of compartmental analysis, is about 22 minutes. In contrast, vacuolar MACC remains sequestered within the vacuole. The transport of labeled MACC into the vacuole is stimulated by the presence of unlabeled MACC in the suspension medium, probably as a result of a reduced efflux of the labeled MACC from the cytosol into the suspending medium.