Uptake of Lupanine by Alkaloid-Storing Epidermal Cells of Lupinus polyphyllus

Abstract

Epidermis of steins and petioles of Lupinus polyphyllus accumulates quinolizidine alkaloids at a concentration of about 30 mM. Since lupanine is synthesized mainly in green mesophyll tissue and not in the epidermis, the alkaloids have to be transported into the epidermal cells. Uptake of [³H]-lupanine into isolated epidermis was 3 to 20 times higher in epidermal cells as compared to the corresponding mesophyll cells. Uptake of lupanine is time dependent and proceeds against a concentration gradient. The uptake depends on temperature and can be characterized by an activation energy of 34 kJ/mol. The process shows multiphasic uptake kinetics and is reduced by SH-group inhibitors (NEM, PHMB) and inhibitors of the energy metabolism (cyanide, antimycine, DNP, CCCP). All these data provide first evidence that simple diffusion cannot be the mechanism for the uptake of lupanine into epidermal cells. The uptake is probably catalyzed by transport proteins.