A Histochemical Study of Embryo Development inVanda(Orchidaceae)

Abstract

Changes in distribution and concentration of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), total proteins, histones, and insoluble polysaccharides were studied by microscopic histochemical methods throughout the development of the embryo and protocorm of Vanda. Total proteins and RNA were found in high concentration in the embryo initial and low concentration in the suspensor initial, whereas, approximately equal concentrations of DNA and histones were present in these cells. An unusually PAS positive cell wall separates the suspensor apparatus from the embryo proper. DNA and histones occur in higher concentration in the large nuclei of the parenchymatous cells than in the small nuclei of the meristematic cells of the protocorm. Total protein and RNA concentrations appear to be equal in the cells of both of these tissues. The walls of the meristematic cells contain proportionately greater amounts of pectin than those of the parenchymatous cells. Methyl esterification of the pectins is low in all cell walls of the protocorm and the major non-pectic wall components are the hemicelluloses.