Temperature-induced reversals of rotation in phycomyces.

The steady state extension and rotation rates of the Phycomyces sporangiophore were measured as a function of temperature. Maximum growth occurred at 27 degrees C; maximum rotation at 28 degrees C. The rotation to extension ratio, a qualitative parameter of cell wall structure, is affected differently by high and low temperatures. Steady state counterclockwise rotation, as opposed to the normal clockwise rotation, was found at both high and low temperatures. The extensional and rotational responses to step changes in temperature were also measured. The conclusions are drawn that a relative decrease in the lysis rate of wall polymer is responsible for the decrease in growth rate at low temperatures, and that a relative increase in the rate of wall synthesis and cross-linking is responsible for the decrease in growth rate at high temperatures. It is suggested that reversals in rotation result from changes in the handedness of the wall's helical structure.