Nuclear transplantation experiments with frog eggs and cell fusion experiments with cultured animal cells revealed that nuclear division (mitosis) is induced by diffusible factors present in cytoplasm. For example, when a cell in G1 phase was fused with a cell in M phase, the G1 nucleus in the fused cell prematurely entered into nuclear division (Rao and Johnson, 1970). This observation suggests that the division of fungal nuclei that are in a common cytoplasm is synchronous. Assuming complete synchrony, the uninucleate A. nidulans conidia (asexual spores) yields a hypha containing 2n nuclei, where n is the number of nuclear divisions after germination. A deviation from this value indicates lack of synchrony. Rosenberger and Kessel (1967) found that synchrony was lost after four to six divisions in individual hypha. In the multinucleate conidia or in the wall-less slime mutant of N. crassa, synchrony was not observed even when the nuclei were present in close proximity in the same cytoplasm (Raju, 1984). Thus nuclei, although residing in a common cytoplasm, control their division individually.
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