Early development of the seed coat of soybean (Glycine max)

Although the development of the soybean ovule has been fairly well studied, knowledge of the sequence of events in the seed coat during the first 3 we eks after flowering is incomplete. The goal of the present study was to doc ument, using light microscopy, the early development of the soybean seed co at with respect to changes in structure and histochemistry. At anthesis, th e seed coat consists of an outer layer of cuboidal epidermal cells surround ing several layers of undifferentiated parenchyma (which together constitut e the outer integument), and an inner layer of cuboidal endothelial cells ( the inner integument). At 3 d post anthesis (dpa), the inner integument has expanded to include three to five layers of relatively large cells with th ick, heavily-staining cell walls immediately adjacent to the endothelium. B y 18 dpa, the outer integument has developed into a complex of tissues comp rised of an inner layer of thick-walled parenchyma, an outer layer of thin- walled parenchyma containing vascular tissue which has grown down from the lateral vascular bundles in the hilum region, a hypodermis of hourglass cel ls, and palisade layer (epidermis). The thick-walled parenchyma of the inne r integument has become completely stretched and compressed, leaving a sing le, deeply staining wall layer directly above the endothelium. At 21 dpa, t he outermost cells of the endosperm have begun to compress the endothelium. At 45 dpa (physiological maturity) the seed coat retains only the palisade layer, hourglass cells, and a few layers of thin-walled parenchyma. The in nermost layer of the endosperm, the aleurone layer, adheres to the inside o f the seed coat. This knowledge will be invaluable in future studies of man ipulation of gene expression in the seed coat to modify seed or seed coat c haracteristics. (C) 1999 Annals of Botany Company.