Conditions for induced fusion of fungal protoplasts in polyethylene glycol solutions

Solutions containing polyethylene glycol MW 6000 (PEG) induced fusion of protoplasts of Penicillium chrysogenum. Balanced heterokaryons were formed by fusion of nutritionally complementing protoplasts. Heterokaryotic fusion products were obtained up to a frequency of 4% of the number of protoplasts, surviving the fusion treatment. Investigation of the conditions, necessary to achieve this high fusion frequency, showed that supplementing the PEG solution with Ca++ and adjustment to high pH gave the best results. Mechanisms of fusion of fungal protoplasts by PEG, calcium and alkaline pH are discussed in view of the obtained results.