Microtubule organization in the differentiating transfer cells of the placenta inLilium spp.

Abstract

Summary. Placental cells in the ovarian transmitting tissue of Lilium spp. are organized as transfer cells with inbuddings facing the ovarian locule. A detailed analysis of microtubule (MT) organization during development of these polarized cells is reported here. Formation of wall projections occurs at the apical part of the cell starting on the day of anthesis, and a fully mature secretion zone is found four days after anthesis. MTs are organized into distinct cortical and central arrays. The cortical array undergoes a unique transition at anthesis. MTs in the basal half of the cell remain in longitudinal bundles while in the apical half of the cell their longitudinal orientation is replaced by a transverse alignment. One day after anthesis, these transverse bundles become a meshwork of short, randomly organized MTs, while MTs in the basal half of the cell retain their longitudinal alignment. The realignment of MTs in the apical half of the cell coincides with the deposition of the secondary cell wall. The central array is composed of short, randomly arranged strands of MTs in the cytoplasm between the nucleus and the apical and basal periclinal walls of the cell. This array first appears as solitary strands in the apical part of the cell one day before anthesis, The central array extends during development and is eventually seen in the basal half of the cell. We propose that MTs in the cortical region near the apical wall act as templates for the deposition of cellulose microfibrils in the secondary cell wall. MTs in the central array in these transfer cells may be involved in the trafficking of vesicles and/or positioning of organelles near the secretion zone.

Calcium-dependent depletion zones in the cortical microtubule array coincide with sites of, but do not regulate, wall ingrowth papillae deposition in epidermal transfer cells

“…Coupling of cellulose synthase complexes and CMTs to achieve cellulose microfibril deposition at right angles to the original wall would require modification of the CMT array. Consistent with this proposition is the reported concurrent CMT reorganization with ingrowth wall construction during transfer-cell trans -differentiation of placental cells of Lilium longifolium ( Singh et al , 1999 ) and of abaxial epidermal cells of V. faba cotyledons ( Bulbert et al , 1998 ). In the latter case, as wall ingrowth papillae deposition commenced, CMTs became polarized to the site of ingrowth wall construction before being randomized to surround developing wall ingrowth papillae.…”

Wall ingrowth architecture in epidermal transfer cells ofVicia faba cotyledons

“…Furthermore, in V. faba cotyledon (Farley et al 2000), seed coat transfer cells (Offler and Patrick 1993), and other transfer cells (Dashek et al 1971, Yeung andPeterson 1974), the cellulose microfibrils in the wall ingrowths are randomly oriented and often arranged in whorls. A similar mechanism for construction of wall ingrowths involving microtubules has been proposed for transfer cells (Singh et al 1999). In tracheary elements and mesophyll cells, aggregations of cortical microtubules underlying the plasma membrane are thought to guide deposition of cellulose microfibrils to build the localized thickenings of secondary-wall material (Giddings andStaehelin 1991, Hogetsu 1991).…”

Floral nectary structure, nectar production, and carbohydrate composition in theLiliumAsiatic hybrid ‘Trésor’

“…(Heinrich 1975;Schnepf and Pross 1976;Nepi et al 2006), Musa paradisiaca L. (Fahn and Benouaiche 1979), and Strelitzia reginae Banks ex Aiton (Kronestedt and Robards 1987) to the secretory surface of Epipactis atropurpurea Raf. (Pais and Figueiredo 1994) and (ii) elsewhere in flowers of Lilium spp., such as at the outer walls of the concave endothelial cells lining the transmitting tract of the style or placenta (Rosen and Thomas 1970;Hu et al 1982;Gawlik 1984;Walles 1992, 1995;Janson et al 1994;Singh et al 1999), and to a lesser degree along the stigmatic papillae in L. leucanthum (Gawlik 1984). This fundamental difference in cellular differentiation may reflect, for nectaries of Lilium, a combined contribution of several layers of nectariferous parenchyma cells and a greater reliance on an apoplastic pathway for nectar preceding its exudation versus a concerted secretory activity by a specialized single layer of canal cells in the style and ovary involved with enhancement of pollen tube growth.…”