Effect of mitochondria on electrofusion of yeast protoplasts

The effect of mitochondria on membrane fusion of yeast protoplasts was investigated in order to regulate electrofusion procedures for yeast breeding. We have found that the cell membrane fusion behavior of respiration-deficient yeasts (p^-) was remarkably different from that of normal yeasts (p⁺). Induction of cell membrane fusion in p⁺ protoplasts appeared under the pulse condition (height: 2.5-5.5 kV cm^-1 and duration: 25-430 μs) after pearl chains were formed. In cell membrane fusants of p⁺ protoplasts, the time interval of morphological change from the long to short state was 3-11 s. On the other hand, induction of cell membrane fusion in p^- protoplasts appeared under the higher pulse condition (height: 4.0-7.0 kV cm^-1 and duration: 20-500 μs). The time interval of the morphological change from the long to short state was 110-170 s in cell membrane fusants of p^- protoplasts. The ζ-potential of p⁺ protoplasts was -10--30 mV and that of the p^- protoplasts was -25--60 mV. The surface charge of the p^- protoplasts was more negative than that of p⁺ protoplasts; therefore, regulation of electrofusion among various kinds of yeast strains was possible by changing the surface charge of the protoplasts using mitochondrial mutations.