Molecular and morphological analyses of maternal inheritance of Chlamydomonas mutants by fluorescence microscopy

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Maternal inheritance is a phenomenon that the characteristics of plastids of only maternal parent are transmitted to all progenies. Therefore we attempted to isolate mutants which have morphologically abnormal characteristics of plastid or plastid nucleoids (pt nucleoids). Two mutant cells (m-1, 2), having about 20 and 50 of plastid nucleoids, respectively, were isolated. Their numbers of pt nucleoids were about two and five times that of wild type cells, respectively. From the physiological analysis, total DNA contents of pt nucleoids per plastid were two and five times that of a wild type cell.Preferential digestion of pt nucleoids derived from a male parent in newly formed young zygotes is thought to be the primary cause of the phenomenon of maternal inheritance of plastids. Usually the frequency of preferential digestion is 100% in the zygotes at 5 h. after crossing between two parents of wild type cells. However, the frequency was 85% in the zygotes when a m-1 cell was used as fem … More ale parent to cross to a male parent of wild type cell. In the zygotes when a m-2 cell was used as the female parent, the frequency was 80%.Genetic analysis showed that each of two mutants had one gene mutation. Two mutations isolated in the present experiment were probably linked because no tetra type tetrads were obtained among 31 tetrads after crossing between two mutant cells.Contrarily, two mutant cells (m-3, 4), having small pt nucleoid number, were isolated. Genetic analysis showed that they had one gene mutation. The results obtained from m-1 and m-2 mutant cells probably indicate that the preferential digestion of pt nucleoids in zygotes derived from these mutants requires a longer period because the frequencies of preferential digestion were not low. This suggests that maternal inheritance occurs independently on the DNA amount of pt nucleoids and opposes a proposal that one of parents having more DNA amount of pt nucleoids can transmit to its plastid characteristics to all progenies. Less