Structure, development and histochemistry of embryo and endosperm in Sesbania speciosa Taub. Ex Engl.

Abstract

Sesbania speciosa Taub. ex Engl. is an introduced plant cultivated in India for fibre, green manure and nutraceutical potential. The development and histochemistry of the endosperm and embryo of this plant have not been yet at all reported and the present study was carried out in an effort to bridge that gap in our knowledge. Two-micrometer sections of seeds of S. speciosa at various stages of development were cut on a rotary microtome. DNA, ribonucleic acid and insoluble polysaccharides were found to be locally localized. It was observed that the ovule of the Sesbania speciosa is campylotropous bitegmic and crassinucellate and the embryo sac is a 7-celled structure. The synergids possess PAS-positive filiform apparatus. All the cells of the mature embryo sac, before fertilization is bereft of polysaccharide grains. The embryo proper, during early embryogenesis, contains a high concentration of proteins and nucleic acids but lacks polysaccharide grains. At the dicotyledonous embryo stage, the concentration of proteins and nucleic acids declines and is followed by the synthesis of polysaccharide grains. The embryo suspensor is massive. The endosperm development is of the nuclear type. At the late globular pre-embryo stage, the micropylar 1/3 of the endosperm becomes cellular leaving the rest free-nuclear. The endosperm cytoplasm and nuclei aggregate in the micropylar region and are rich in total proteins and nucleic acids. The concentration of these metabolites, however, declines when the endosperm becomes cellular. The aleurone layer, in mature seed, is rich in proteins and nucleic acid compared to the other persisting endosperm layers.