The ultrastructure of the development of Tillandsia (Bromeliaceae) trichome

Tillandsia spp. (Bromeliaceae) use their epidermal trichomes for absorbing atmospheric water, mineral and organic nutrients. The absorbing trichome in Tillandsia has a nail-like shape, formed by an axis (stem) connected to the internal tissues of the leaf, and by an external shield. Water and aqueous liquids coming from the external environment go through the shield cells and then run through the stem, finally reaching the underlying mesophyll parenchyma along a symplastic route. In this contribution we discussed the ultrastructure during the ontogeny of the trichomes in Tillandsia aeranthos, with particular attention to the last stage, in which the shield cells die at maturity achieving a function in the absorption mechanism. Some features of this last stage of development are similar to those observed in Programmed Cell Death in other cases in plants. Moreover, particular morphological features are described for the first time in relation to cell death: spherical bodies along the walls and wall pores between the shield cells. This is the first time that intercellular channels between somatic cells are described in plants (excluding the conductive system). This particular morphological syndrome was tentatively related to the speed of the last developmental stages of trichomes and to the necessity for the plant to recover rapidly organic material from living trichomes before their death.