Sites of leucine, arginine, and glycine accumulation in the absorptive trichomes of a carnivorous bromeliad

Ultrastructural localization of leucine, arginine, and glycine in the nutrient absorptive trichomes of the bromeliad Brocchinia reducta was achieved through a precipitation reaction with osmium tetroxide. Leaves incubated with amino acid solutions, then fixed with glutaraldehyde and postfixed with OsO₄ exhibited within the trichomes site specific accumulations of an electron-dense precipitate which were absent in distilled water-incubated controls. Four regions of leucine accumulation occurred: (i) in the outer trichome walls, (ii) within mitochondrial cristae, (iii) on the surface of lipid bodies, and (iv) in tubular invaginations of the inner envelope membrane of plastids. Glycine-incubated leaves had dense deposits in the mitochondrial matrix. Arginine-treated tissue had deposits only within the outer trichome walls. The initial glutaraldehyde fixation stabilized accumulations of the amino acid by reacting with the primary amine groups to form a Schiff's base. Subsequent OsO₄ postfixation was presumably oxidative with OsO₄ being reduced to an insoluble form.