Submitted to: Plant Cell Tissue And Organ Culture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2001
Publication Date: N/A
Interpretive Summary: Plant breeders have had limited success improving the sugar content in sugarbeet due to an inverse relationship between yield and taproot size. Further optimization of sucrose storage capacity will, therefore, require genetic manipulation based on novel concepts such as genetic engineering. The use of plant growth regulators, specifically cytokinins, has been suggested as a possible way to increase sugar yield and concentration in large taproots by increasing the number of sucrose accumulating cambial rings with shorter diffusion paths between the translocation system and the nearby cells accumulating sucrose. We, therefore, constructed a cytokinin synthesizing gene for production of cytokinins in the taproot and introduced it into sugarbeet. Although taproot cytokinin levels were elevated in these plants, all exhibited greatly reduced taproot biomass and sugar content at maturity. In younger plants, however, sucrose appeared to accumulate to much higher levels than in plants not carrying the cytokinin gene but this trend failed to continue to maturity. This research generates new approaches for use by other scientists working on improving sugar yields from sugarbeet.
Technical Abstract: The effects of a bacterial cytokinin biosynthesis gene fused to a patatin gene promoter were studied in sugarbeet (Beta vulgaris L.). Leaf zeatin and zeatin riboside concentrations were 18 and 8-fold greater in two independent transformed clones compared with the untransformed control, while a corresponding 2-fold increase was measured in the taproots of both transformants. Elevated cytokinin levels were associated with distinguishable morphological alterations that have been commonly observed in ipt transformants, i.e. less root growth and leaf surface area, as well as increased axillary shoot development. Leaf concentration of the major nonstructural carbohydrates, sucrose and gluclose, were not significantly different from those in control plants except for the highly elevated levels of glucose in one of the transformants. Taproots of 8 to 12-month-old transgenic plants were much smaller and had lower carbohydrate concentrations as compared to the untransformed controls.