Studies of Macrostome Formation of Low-Transforming Tetrahymena vorax. Transformation Enhancers,Generation Time,and Membrane Fluidity1

ABSTRACT. Periodically, stocks of Tetrahymena vorax, which normally yield 70–90% macrostomes when subjected to heat shock or other induction methods, become low-transformers and yield ≥30% macrostomes. The addition to the post-heat-shock wash buffer (pH 6.8) of 2.7 × 10^-4 M Fe³⁺, 1.6 × 10^-5 M Cu²⁺, 1 × 10^-4 M retinol palmitate or the adjustment of the buffer to a pH of 4 to 5 boosts transformation significantly over controls in inorganic medium alone. The addition of Fe²⁺ or Cu¹⁺ has a similar, but less pronounced effect on transformation. Ferric ion (2.7 × 10^-4 M) will significantly increase transformation in starved non-heat-shocked cells, whereas Fe²⁺, copper, retinol palmitate, and hydrogen ion concentration have no effect. The agents that boost transformation appear to act by delaying cell division in pre-transformants. Membrane fluidity, as inferred by fluorescence polarization measurements of 1,6-diphenyl-1,3,5-hexatriene, is altered in a consistent manner by starvation and heat shock. Enhancing agents, including compounds previously shown to boost heat-shock-induced macrostome formation, produce diverse shifts in membrane fluidity. Their effect on transformation of these low-transforming cells therefore appears to be attributable to some mechanism or mechanisms other than a direct alteration of membrane physical properties.