Ultrastructural Changes of the Mature Embryo Sac in Buckwheat (Fagopyrum esculentum) as a Result of High Temperature Exposure

Abstract

The ultrastructure of the mature embryo sac of common buckwheat (Fagopyrum esculentum) was studied under normal and high temperature conditions with transmission electron microscopy. The mature embryo sac consisted of a central cell and an egg apparatus that included an egg cell and two synergids. The cytoplasm of the egg apparatus is distributed characteristically in polar side. The fused nucleus of the central cell is located near the egg apparatus. The cytoplasm of the egg and central cell contained abundant mitochondria, ribosomes, plastids and rough endoplasmic reticulum (rER). In the cytoplasm of the synergids there were massive strands of parallel rER, dictyosomes and vesicles derived from dictyosomes and rER. When exposed to high temperature conditions in summer, the egg apparatus shows various features of degeneration, i.e. the accumulation of osmiophilic deposits in egg cells and synergids, collapsed synergids, incomplete membrane systems and enlarged rER in egg cells. These degeneration phenomena cause functional alterations that disrupt normal fertilization.