Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: June 24, 1998
Publication Date: N/A
Technical Abstract: Cytokinins as major plant growth regulators are involved in a wide range of physiological and biochemical processes. They upregulate secondary metabolic pathways, products of which have insecticidal and antimicrobial properties. In sugarbeet taproots, increased cytokinin levels have been correlated with cambial initiation and rapid cell division periods. To increase endogenous cytokinins in sugarbeet, a bacterial cytokinin biosynthesis gene, ipt, was fused to a wound-inducible proteinase inhibitor II (Pin2) tuber-specific patatin (Pa) gene promoters from potato. Agrobacterium-mediated cotyledon transformation or particle bombardment of embryogenic callus yielded one Pin2-ipt and two Pa-ipt plants. Putative transformants were identified by PCR and placed on root inducing medium. To compensate for the elevated cytokinin levels, two previously obtained Pa-ipt shoots were exposed to high auxin concentrations (50 mg IBA/ml) for a 24 hour period for root initiation as compared to continuous 3 mg IBA/ml for normal shoots. Pa-ipt shoots rooted in 4-8 weeks in comparison to 2 weeks for controls. One of the transformants appeared normal except for increased adventitious shoot development and the other exhibited dark green leaves and reduced apical dominance, all typical cytokinin effects. Approximately a 3-fold increase in sucrose levels was observed in the dark green leaves but the taproot levels were unchanged. Levels of the cytokinins zeatin and zeatinriboside in leaves and taproots of the Pa-ipt transformants were up to 20 and 2 times higher, respectively, than in normal plants. Analyses of the transgenic plants for resistance to the sugarbeet root maggot and sucrose content are in progress.