Ajmalicine Transport into Vacuoles Isolated from Catharanthus Roseus Cells
We have studied previously the compartmentation of ajmalicine in Catharanthus roseus cells (Renaudin and Guern, 1982; Renaudin et al., 1985) and of nicotine in Nicotiana tabacum and Acer pseudoplatanus cells (Kurkdjian, 1982). The behavior of the 14C-labelled alkaloids added in the cell suspensions was in good agreement with the predictions of the so-called ion-trapping model: These alkaloids apparently diffused passively through the plasmalemma and the tonoplast, mainly under their neutral form, and did accordingly distribute between the cells and the medium. They were accumulated within cells, likely in vacuoles, against a concentration gradient, because of the relative acidity of the vacuolar compartment and of the low capacity for diffusion of the alkaloid cation. The distribution of alkaloids between the cells (i.e. the vacuoles) and the medium was dynamic and it was a function of 1) the acidity constant of the alkaloid, and 2) the pH difference between the vacuole and the medium. Due to the high pH (ca. 7.5) and low relative volume (less than 20%) of the cytoplasm, the accumulation of this compartment was likely neglectable. It was assumed that accumulation in whole cells merely reflected the accumulation within vacuoles, thus allowing the indirect approach of vacuolar properties.
KeywordsIndole Alkaloid Tritiated Water Acidity Constant Vacuolar Compartment Plant Vacuole
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