Owen & Thomson 1991 (Article) Brocchinia, trichomes

Structure and function of a specialized cell wall in the trichomes of the carnivorous bromeliad Brocchinia reducta

Author(s):—T.P. Owen Jr. & W.W. Thomson

Publication:—Canadian Journal of Botany 69(8): 1700-1706. (1991) — DOI

Abstract:—The leaves of the carnivorous bromeliad, Brocchinia reducta, are clustered in a tight vertical rosette, forming a water-collecting tank in which insects are trapped. Evidence in the literature indicates that nutrient uptake into the leaves occurs primarily, if not entirely, via trichomes located at the base of the leaves on the tank side. The outer cell wall in the trichomes from the carnivorous bromeliad B. reducta has an unusual ultrastructure. This wall has a labyrinthine-like appearance of light and dark-staining regions that suggests a highly specialized function. This study examined three structural aspects of this wall. First, the limiting porosity of the trichome wall was examined with fluorescently labelled dextrans and shown to permit the transport of molecules as large as 6.6 nm. Second, structural changes in a dehydrated wall were observed using freeze-substitution techniques. Specifically, the electron transparent wall "regions" were collapsed when the trichome was dried. Last, the presence of periodic acid soluble polysaccharides was detected throughout the electron-dense wall protuberances, but occurred only as thin, dispersed strands in the more electron-transparent regions. We have concluded from these studies that in the hydrated state, these electron-transparent regions represent the channels through which solutes move through the wall to the cap cell surface. A pore size of 6.6 nm would also permit the movement of modest-size proteins, and based on previous observations, we suggest that protein uptake into the cells would occur by pinocytosis. We found channels can vary in size and thus porosity; in the dehydrated state, the wall is considerably shrunken and the channels collapse. We hypothesize that the shrunken wall restricts the loss of water from leaves through trichomes to the atmosphere.

Keywords:—Bromeliaceae, cell wall porosity, fluorescently labelled dextrans, freeze-substitution, Thiéry staining.