Structure and function in absorption and transport of nutrients

Abstract

The term transfer cell applies to cells that are thought to be particularly active in transport of inorganic or organic solutes across the plasmalemma. Structurally the most significant feature is the differentiation of cell-wall protuberances on the inner surface of the wall. These wall ingrowths — which often form a considerable wall labyrinth — are surrounded by the plasmalemma, which is therefore largely increased. Transfer cells are regarded as analogues of the microvilli in many animal cells, which are specialized in transport processes. It is widely held that in both systems the amplified plasmalemma surface leads to a largely increased number of pumping sites per cell, thus promoting active transport at the symplast/apoplast border [1]. The occurrence of transfer cells has been demonstrated to be common in all plant organs. In roots, transfer cells are common in the xylem parenchyma of leguminous nodules [7] as well as in rhizomes [8]. However, until 1976 no transfer cells had been described that could be directly related to the absorption of nutrients by the root and their transport to the shoot.