Changing rates of uptake of [3H]leucine and other compounds during culture of tobacco mesophyll protoplasts

The rate of uptake of [3H]leucine by tobacco mesophyll protoplasts increased several-fold during the first 8 h in culture at 22 deg C, remained at this higher level for about 12 h, and then declined slowly until after 45 h in culture it was at or below the original rate. The increase in rate was observed not only with protoplasts in various physiological conditions but also with isolated cells, and was due neither to recovery from the trauma of centrifugation nor to depletion of a nutrient or accumulation of a product in the medium. It was prevented by cycloheximide or puromycin but not by chloramphenicol. Although the actual rates of uptake were different, similar changes occurred with [3H]uracil, [3H]UTP, [14C]glucose and [32P]phosphate