Apoplastic and ultrastructural characterizations of the trichomes from the carnivorous bromeliad Brocchinia reducta

The ultrastructure of the trichomes from the carnivorous bromeliad Brocchinia reducta was studied. The foliar trichome occurred in a cutinized epidermal crypt and was differentiated into cap, stalk, and foot cells. Unlike members of other bromeliad genera, the approximately 30 cells in the cap were alive at maturity and possessed an unusual labyrinthine-like wall organization. Irregularly shaped, dense wall regions that were separated by electron-transparent interstices extended from a thin, primary wall. This system appeared to constitute an elaborate system of channels specialized for nutrient uptake, a role which is consistent with the observed localization of the apoplastic tracer lanthanum. Moreover, cuticular gaps were noted where the cap cells face the tank cavity. These openings were the only site of solute entry into the gland. Cap cells possessed much plasmalemma blebbing and contained numerous coated vesicles and coated plasmalemma regions, all suggesting specializations for absorption and possibly secretion. Experiments using lanthanum as a tracer indicated that an apoplastic continuum exists from the cap cells to the underlying mesophyll, and that this system might provide a diffusive pathway for nutrient uptake.