High-density induction of a quiescent cell state in Physarum polycephalum.

The non-histone protein complement of Physarum polycephalum changes rapidly when microplasmodia are subjected to conditions of high density. The changes in these proteins induced by high density are similar to the changes observed during starvation-induced encystment. A 50% decrease in DNA synthesis, observed after 7 h of starvation, is observed after only 1 h of high density. High density also results in a decrease in RNA synthesis comparable to decreases induced by prolonged starvation. Total heterochromatin increases in response to either high density or starvation. Increased heterochromatization is preceded by an increase in nuclear actin. Mitochondrial morphology and cytoplasmic organization are also similarly altered by starvation and high density. These observations suggest the possibility of a generalized mechanism for cellular transition from active growth to a non-proliferative cell state.