The uptake of phenylalanine into suspension-cultured cells of Atropa belladonna

When suspension-cultured cells of Atropa belladonna L. were in late growth phase, phenylalanine, one of the early precursors of atropine, was taken up mainly by diffusion without carrier but also actively via mediated transport. The uptake capacity of different callus lines varied from 0.4 to 1.9 μol (g fresh weight)⁻¹ h⁻¹ with an optimum pH at 4.5 or 5.0, depending on the callus line, 2,4-Dinitrophenol (DNP) and KCN inhibited about 35–45% of the total uptake in all tested callus lines, so that a part of the uptke was dependent on metabolic energy.
The rate of phenylalanine uptake was fastest from 2 to 7 days after the start of the suspension culture. The increase was from 50 to 300%, depending on the cell line. The enhancement was mainly due to increased mediated uptake and could be inhibited by cycloheximide during the first days of the suspension culture. Glutamine, added to the nutrient medium, also prevented the increase. The inhibition caused by glutamine together with cycloheximide was not additive. Obviously, glutamine did not directly affect the carrier, but possibly repressed its synthesis. When cells entered the stationary phase, the total uptake began to decrease, and most of it was non-mediated. The suspension cultures of A. belladonna had only limited capacity to regulate the transport of phenylalanine into the cells at this phase of growth.