Expression of Cell Division Cycle Related Genes in Beta vulgaris L. Storage Organs and Cells in Suspension Cultures

Abstract

The sucrose storage capacity of the sugar beet, Beta vulgaris, storage organ has been related to its anatomy. A transverse section of the storage organ reveals a pattern of concentric rings which is caused by the alternation of vascular zones with parenchymatous zones. Sucrose is transported to the storage organ via the phloem and moves laterally to the adjacent parenchymatous tissues, where it is stored in the cell vacuoles. The storage organ of sugar beet has 12–15 cambia, the divisions of the 6 inner rings provide the cells which make up some 75% of the storage root while the outer rings (9 and above) make almost no contribution to the bulk of the storage root. It has been found that the small parenchymatous cells close to the phloem accumulate sucrose to a higher concentration than that achieved by large (older) cells remote from the phloem. Hence, it is predicted that for optimum sucrose accumulation the storage organ should have a large number of parenchymatous zones, each of which offers a short diffusion path from the phloem to predominately small storage cells. In order to manipulate sugar beet development toward this optimum it is necessary to have an understanding of the processes that regulate cell division, cell expansion and differentiation. Towards this end we have begun to isolate and characterise cell division cycle related genes from sugar beet and we have developed a cell suspension culture system for analysis of their roles (Elliott et al. 1996).