Leucine Uptake and Incorporation by Convolvulus Tissue Culture Cells and Protoplasts under Severe Osmotic Stress

Abstract

AbstractThe uptake and incorporation of radioactive leucine by Convolvulus arvensis L. suspension culture cells were studied under various osmotic conditions to provide information about the effects of osmotic stress at the cellular level and about the suitability of various osmotica for stabilizing protoplasts. When manitol, sorbitol, sucrose, or a mixture of CaCl2 and KCl was added to the cells at a concentration normally used to stabilize protoplasts, the uptake of leucine was inhibited by 50 to 60% and incorporation by 37% with no major differences detected among these osmotica. NaNO3 of a similar osmotic strength exerted considerably more inhibition, an inhibition that was reversed by as little as 10 mM simultaneous CaCl2. None of the osmotica altered leucine or protein leakage from the tissue. In general, external solute concentrations below 0.36 osmolal slightly enhanced uptake and incorporation. At successively higher concentrations, uptake and incorporation decreased in a linear fashion, with no apparent discontinuity in the rate of decrease as the cells plasmolyzed. Cycloheximide inhibited both the uptake and the incorporation of leucine in all osmotic situations tested, exerting a much stronger inhibition upon the uptake by control tissue than upon that by cells in osmotica. Different cellulase enzyme preparations varied considerably in their effects on subsequent leucine uptake and incorporation.