Development of Techniques for the Isolation of Genes Expressed in the Shoot Apex of Sugar Beet (Beta vulgaris)

Flowering plants are the most complex and highly evolved organisms within the plant kingdom. The process of flowering is regulated by a combination of intrinsic and environmental factors which signal the switch from vegetative to floral development. The molecular mechanisms involved in this process are poorly understood, and although there have been many models put forward to try to explain the way in which the environment interacts with these intrinsic factors to bring about floral induction at the shoot apex, no one model has been shown to satisfy every case. The sugar beet plant {Beta vulgaris) is commercially important due to its ability to store a large concentration of sucrose in its expanded tap root (the beet). Beta vulgaris exists in two growth forms, annual and biennial. Both are obligate long day plants (LDP) but the biennial requires an additional period of cold treatment (vernalization) prior to exposure to the long days. A substantial amount of the sugar beet crop is lost each year due to a phenomenon referred to as bolting. Here the biennial beet flowers in its first growing season as a consequence of exposure to low temperature early in that growing season and, therefore, loses its supply of sucrose to the formation of the flower stalk. There are also several biennial genotypes of sugar beet that require very specific environmental growth conditions for the induction of flowering. Generating seed from these plants, and thus maintaining these lines of biennial beets, can be very difficult. To understand, and be able to control, flowering in sugar beet crops at the molecular level would, therefore, be of advantage to both the sugar beet grower and to the breeder. It is known that the annual beet plant possesses a gene, B, which confers annuality upon the beet plants. This gene shows almost complete Mendelian dominance over the gene for bienniality. Since the biennial requires vernalization to induce flowering it is possible that the vernalization process induces changes within the biennial that allow the expression of this B gene, or some other gene specific to the biennial plant. Alternatively the biennial may not contain a functional B gene product. The process of vernalization is known to be perceived at the shoot apex. Hence, in this study the shoot apices of annual sugar beet plants that had experienced non-floral-inductive conditions (short days, 2