Cyclic adenosine monophosphate and the development of polysphondylium

Abstract

Centre formation in Polysphondylium violaceum is delayed for 2 h on buffered agar containing 10⁻³ M c-AMP, and for up to 22 h on unbuffered agar with the same c-AMP concentration. With ambient c-AMP concentrations as low as 10⁻⁸ M, P. pallidum forms numerous, small, atypical aggregates which do not fruit. This effect is independent of whether the agar is buffered. P. violaceum amoebae are weakly attracted to the tip of a microelectrode containing 10⁻³ or 10⁻⁴ M c-AMP, but the electrode cannot compete when natural centres form nearby. P. pallidum amoebae are not attracted. Aggregates of P. violaceum and of P. pallidum are strongly attracted to a microelectrode releasing c-AMP. The observation of Shaffer that Polysphondylium grex switch over from secreting an acrasin that attracts homologous amoebae to one that attracts the larger Dictyo- stelium species suggests that the second acrasin might be c-AMP. The above results strengthen this conjecture. As c-AMP inhibits centre formation, the secretion of c-AMP by older aggregates may explain an inhibition of centre formation in the ‘ overlay’ experiments of Shaffer.