Transfer Cells: Cells Specialized for a Special Purpose

Abstract

Transfer cells are plant cells with secondary wall ingrowths. These cells are ubiquitous, occurring in all plant taxonomic groups and in algae and fungi. Transfer cells form from differentiated cells across developmental windows and in response to stress. They are considered to play a central role in nutrient distribution by facilitating high rates of transport at bottlenecks for apo-/symplasmic solute exchange. These properties are conferred by their unique structural features--an invaginated secondary wall ensheathed by an amplified area of plasma membrane enriched in a suite of solute transporters. Recent development of transfer cell experimental systems, combined with technologies to image the three-dimensional structure of wall ingrowths, is allowing identification of inductive and regulatory signals, discovery of sequential processes involved in their differentiation, and a search for transfer cell identity genes. A model of key events in differentiation of a transfer cell is presented to highlight areas for future investigation.

Spatio-Temporal Dynamics of Fructan Metabolism in Developing Barley Grains

“…High rates of solute transport across transfer cell membranes are ensured by the orchestrated action of transporter proteins, H + -ATPases, and cation channels (Offler et al, 2003). In the 5 to 15 DAP barley ETCs, Hv-SUT1 (encoding a sucrose/H + symporter) transcript is particularly abundant (Weschke et al, 2000).…”

“…Grain filling relies on an unhampered import of assimilate from the mother plant, mainly in the form of sucrose, channeled from the vascular bundle via cells of the ventral crease into the endosperm. The NP and ETCs represent the maternal-filial boundary and control the assimilate transfer toward the endosperm (Wang et al, 1995a;Offler et al, 2003). At the beginning of the storage phase, a large apoplastic gap (the endosperm cavity) emerges between the NP and ETCs (Figure 1B), and the morphology of the cells facing this cavity has been shown to resemble that of transfer cells (Weschke et al, 2000;Patrick and Offler, 2001).…”

The Maize Transcription Factor Myb-Related Protein-1 Is a Key Regulator of the Differentiation of Transfer Cells

“…Histological studies have identified modified TCs strategically positioned at the interfaces where solute exchange takes place (reviewed in Offler et al, 2002), such as the loading areas of minor leaf veins, areas surrounding the vascular bundle at stem nodes, points of glandular secretion, and places of delivery of nutrients at sink organs (i.e., at the base of flowers and fruits). Highly differentiated TCs have also been found at the symplastic discontinuities between individuals belonging to different generations (e.g., at the interface between gametophyte and sporophyte generations [Ligrone and Gambardella, 1988] and at the base of seeds [Kiesselbach, 1949;Cochrane and Duffus, 1980;Offler and Patrick, 1993;Talbot et al, 2001]) and symbiotic species (e.g., at mycorrhizal and rhizobium-root nodule interfaces [Gunning et al, 1974;Allaway et al, 1985]), and even at points of plant-parasite interaction (e.g., in nematode infections [Jones and Northcote, 1972]).…”

“…Little is known about the molecular signals that induce TC differentiation, but it is likely that transported solutes are involved (Offler et al, 2002). Certainly, it has been shown that a transient increase in monosaccharide concentration early in development induces the differentiation of TC in the adaxial surface of fava bean (Vicia faba) cotyledons (Offler et al, 1997;Farley et al, 2000).…”

A RING Domain Gene Is Expressed in Different Cell Types of Leaf Trace, Stem, and Juvenile Bundles in the Stem Vascular System of Zinnia

“…3C) reveal elaborate labyrinthine cell wall invaginations in the xylem parenchyma cells. Cells with this adaptation are commonly known as transfer cells and are characteristic of nodal xylem parenchyma (Pate and Gunning, 1972;Offler et al, 2002).…”