A study on behavior of the plastids during the sexual reproduction of higher plants.

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Changes in morphology and the number of plastids and mitochondria in unfertilized egg cells of Solanum melongena before and after pollination were described, using techniques of electron microscopy of serial sections and three-dimensional reconstruction.The egg cell in a mature embryo sac examined contained 30 plastids and 137 mitochondria. Half the plastids were surrounding the egg nucleus which was located at the chalazal end of the cell. In contrast, only 15% of the mitochondria were perinuclear.After pollination but before reaching of the pollen tube to the egg apparatus, marked changes were observed on the number, configuration and distribution of both plastids and mitochondria in the egg cell. The number of the plastids decreased to 14 or at most 19. The volume of the plastids on average increased and five of them were branched and elongated in configuration. Nucleoids of the plastids in the egg cell were difficult to detect in the section by electron microscopy either before or after pollination. The change was more drastic with the mitochondria. The number of the mitochondria decreased to 17 or at most 22. Seven of them were 'giant mitochondria' of extremely elongated, branched and entangled configuration. In these mitochondria nucleoids were conspicuously observed.The observations suggest that reduction of the number of the plastids and mitochondria occurs in the egg cell just before fertilization. It is most likely that this may be caused by organelle fusion.