Abstract:Calmodulin inhibitors CFZ and TEP inhibited phytochrome controlled rotation of mougeotie chloroplast within the concentration range from 10-7 to 10-6 mol/l. The chloroplast rotation restored when the treated Mougeotia threads were transfered to fresh culture medium. Adding extraneous 1 m mol/1 ATP, the inhibition effect of calmodulin inhibitors was greatly reduced. It is supposed that calmodulin probably involved in the mechanism of Mougeotia chloroplast rotation. The effecting site of calmodulin on the inhibition mechanism as well as the significance of this research to the phytochrome primary reaction was also discussed.