Erect Glandular Trichomes of Medicago scutellata (L.) Mill.: Gland Development and Early Secretion

Abstract

Gland development and early secretory activity of erect, capitate-stalked glands of Medicago scutellata (L.) Mill. were studied by light and electron microscopy because the glands provide defense against larvae of the alfalfa weevil, Hypera postica (Gyl.). Observations were made from the apices of stipular teeth, which form glandular tissue equivalent to that of erect glands. In gland development an epidermal initial forms a seven-celled filament by transverse divisions. Vertical and oblique divisions in cells 6 and 7 of the filament produce a globose head of 12-20 cells. In presecretory stages, cells of the gland head contain spherical vacuoles created by dispersal of the cell vacuole. These vacuoles acquire clumps of electron-dense material along the inner membrane surface. Isodiametric bodies (IB) in membrane-bounded aggregates appear to associate with vacuoles and may be a precursor of the presecretory dense material. Granular bodies in the cytoplasm, similar to IB, may be another secretion precursor ...