Cytoplasmic changes accompanying the female meiosis in Lilium longiflorum Thunb.

The events that accompany female meiosis in Lilium parallel almost exactly those characteristic of male cells. The megaspore mother-cell is first cut off from investing tissue by a callosic wall, and this isolated cytoplasm undergoes a phase of comprehensive dedifferentiation. Not only does the major part of the ribosome population appear to be removed from both the cytoplasm and plastids, but also the plastids themselves dedifferentiate to such a degree that they represent almost the sole expression of their genome. Following meiotic prophase the cytoplasm redifferentiates. The ribosomes return by means of the disintegration of cytoplasmic nucleoloids derived from material originally produced at the nucleolar organizer in pachytene, and the plastids redifferentiate into amyloplasts. The mitochondria also exhibit a similar, but less extreme, cycle of differentiation during which a proportion of their population appears to be eliminated. As in the male cells, the megaspore mother-cell energy reserves are converted from starch to lipid in early meiosis, and a low level of protein synthesis appears to be maintained within encapsulated regions of cytoplasm, protected by membranous envelopes from the hydrolytic enzymes present. Since these cycles of differentiation appear common to both sexes of a higher plant, they must be regarded as forming a significant component of the plant life-cycle. Their precise roles have yet to be clarified, but most certainly they must include the elimination of those informationcarrying molecules characteristic of the diploid phase of growth, and the provision of a fresh and efficient cytoplasm for the expression of the new haploid genome.