American Journal of Botany 78(8): 1113-1122. 1991.
Paul G. Mahlberg & Eun-Soo Kim
Department of Biology, Indiana University, Bloomington, Indiana 47405; and Department of Biology, Soonchunhyang University, Choongnam, Korea
Keywords: Cannabis sativa, Cannabaceae, gland, trichome, cuticle
The dermal sheath of glandular trichomes of Cannabis sativa L., consisting of cuticle and a subcuticular wall, was examined by transmission electron microscopy. Cuticle thickened selectively on the outer wall of disc cells of each trichome prior to formation of the secretory cavity, whereas thickening was less evident on the dermal cells of the bract. Membraned secretory vesicles that differ in size and appearance in the secretory cavity were the source of precursors for synthesis of cuticle. Vesicle contents, released following the degradation of the vesicle membrane upon contact with the subcuticular wall, contributed to both structured and amorphous phases of cuticle development. The structured phase was represented by deposition and thickening of cuticle at the subcuticular wall-cuticle interface to form a thickened cuticle. In the amorphous phase precursors permeated the cuticle in a liquid state, as shown by fusion of cuticles and wax layers between contiguous glands, and may have contributed to growth in surface area of the expanding sheath. Disc cells are interpreted to control growth of secretory cavity by secretion of membraned vesicles into the cavity. The thickened cuticle, which increased eightfold in thickness during enlargement of the gland, provided structural strength for the extensive surface area of the dermal sheath. The gland of Cannabis in which vesicle contents contribute to the growth in thickness and surface area of the cuticle of the sheath is interpreted to represent a phylogenetically derived state as contrasted to secretory glands possessing only cuticle and lacking a complement of secretory vesicles.