SYNOPSIS. The size, composition and physiology of average cells have been studied in cultures of Acanthamoeba castellanii during the phases of logarithmic growth and population growth deceleration (PGD). Most of the features examined were relatively constant during log phase, but had significant changes during PGD. Average cell volume increased about 60% and total dry mass about 15–20% during the latter period. Total protein content remained constant thruout both growth phases, but cytochrome oxidase doubled during PGD. DNA, RNA and glycogen levels began to change during late log phase. DNA decreased about 50% and RNA increased about 75%. Glycogen decreased 50% during the RNA build‐up and then increased to a plateau above the log phase level. A final decrease in glycogen followed an increase in the relative numbers of cysts in late PGD. It was found that PGD begins when O2 becomes limiting and evidence that the subsequent changes in macromolecule composition are related to encystation is discussed.

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Changes in the levels of DNA and RNA syntheses have been studied in unagitated cultures of Acanthamoeba castellanii during the phases of logarithmic multiplication (LM) and population growth deceleration (PGD) . Pulse-labeling experiments show that the rate of DNA synthesis decreases at the same time that DNA per cell is known to drop by 5017, The drop in DNA content has been explained by demonstrating with hydroxyurea that the majority of LM amebas can replicate once when DNA synthesis is inhibited and, therefore, must be in G2, whereas the PGD amebas cannot multiply in the presence of inhibitor and, therefore, must be in G1 . The inhibition of DNA synthesis in LM or PGD cells has been shown to induce encystment . The rate of RNA synthesis, as illustrated by pulse-labeling experiments, increases 25% in late LM-early PGD while RNA per cell increases 75 0/0 . The rate of synthesis then decreases 65% . The majority of accumulated RNA has been demonstrated to be ribosomal by disc electrophoresis . By using actinomycin D at different stages during the RNA build-up, the ability of the amebas to encyst has been shown to depend on the presence of this RNA . The observations on DNA and RNA are discussed with respect to the occurrence of cysts in the cultures during PGD .

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Laminin, a noncollagenous glycoprotein, was observed in the mouse ovary using a direct immunofluorescence technique. Laminin was localized within the basal lamina underlying growing and atretic ovarian follicles, blood vessels, and the germinal epithelium. In addition, laminin was also present at the periphery of individual corpora lutea cells. The presence of laminin in the basal lamina underlying ovarian follicles may be important for the passage of material between the follicle cells and the connective tissue stroma. In addition, its location around the corpora lutea cells may reflect an involvement in cell to cell contact as well as intercellular communication.

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