Sugar beet root as an organ for sucrose accumulation

Abstract

In parenchyma cells of the sugar beet root, sucrose accumulates in large central vacuoles formed at a very early stage of root development. The growth of parenchyma cells is mainly the result of vacuole volume increase, small individual vacuoles being replaced by a single central vacuole. For apoplastic solute movement, cell walls and intercellular spaces may be used, the latter being well developed in young roots [2]. Later, an intensive thickening of cell walls takes place followed by an alteration of their structure [1]. In growing roots, plasmodesmata may also serve for sucrose movement. Plasmodesmata between parenchyma cells are located in large groups in relatively thin regions of the cell walls. They are branched in two directions with large median cavities which seem to unite all the plasmodesmata of a zone (Fig. 1). Although sucrose is really a principal reserve product in the sugar beet root, starch accumulates in plastids in large amounts (Fig. 2). Therefore, the sugar beet root can transform sucrose arrived from leaves into starch, however starch content is very low since plastids are small and sparse.