A Histochemical Study of Embryo Sac Development inVanda(Orchidaceae)

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Abstract
Changes in distribution and concentration of insoluble polysaccharides, total proteins and ribonucleic acid (RNA) were studied by microscopic histochemical methods throughout the development of the embryo sac of Vanda. The megaspore cell wall is different structurally and/or chemically from that of other megasporangial cells. A protein and RNA gradient exists in the megasporangium with the higher concentration toward the megaspore. The egg cell is low in total proteins, RNA and insoluble carbohydrates, while the synergid cells are high in these constituents and have a distinct filiform apparatus. RNA and proteins are high initially in the primary endosperm nucleus, the concentration subsequently decreasing until the disappearance of this cell. The antipodal cells are low in insoluble carbohydrates, protein and RNA. Shortly before fertilization, protein concentration in the embryo sac cytoplasm rises without a preceding RNA increase. Protein concentration in this area diminishes after fertilization.