A method for the selection of mutants of Phycomyces blakesleeanus defective in germination

Summary A simple method for the physical separation of dormant and germinated cells of Phycomyces blakesleeanus has been designed. Separation was attained by isopycnic centrifugation in a preformed discontinuous density gradient of Urografin. In this gradient, dormant spores and active cells at two different stages of germination were separated in three homogeneous and clearly distinct bands. The method has been used to follow the kinetics of the variation of cellular density during germination of wild type spores and to select for mutants temperature-sensitive for heat-shock induced germination. Sixty-nine mutants have been isolated by various procedures which include a separation step in the described Urografin gradient.