Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2005
Publication Date: 6/1/2006
Citation: Klotz, K.L., Finger, F.L., Anderson, M.D. 2006. Wounding increases glycolytic but not soluble sucrolytic activities in stored sugarbeet root. Postharvest Biology and Technology. 41:48-55. Interpretive Summary: Sugarbeet roots are inevitably wounded by harvest and piling operations. To heal wounds, carbon compounds and energy are required, and this requirement is met by degrading sucrose. Sucrose degradation requires the initial breakdown of sucrose to invert sugars (sucrolysis). Invert sugars are then broken down into organic acids by the glycolysis pathway. To understand the mechanism which regulates sucrose degradation for wound-healing, the activities of six key sucrolytic and glycolytic enzymes were determined in wounded and unwounded roots stored at 10oC for 13 days. The enzymes that catalyze early glycolytic reactions were induced in wounded roots, while enzymes involved in the degradation of sucrose to invert sugars and the final step of glycolysis were unaffected. The induction of early glycolytic enzymes suggests that these enzymes may have a role in the regulation of sucrose breakdown to support wound-healing processes.
Technical Abstract: The wounding of sugarbeet (Beta vulgaris L.) roots by harvesting and piling operations increases the demand for sucrolytic and glycolytic products for wound-healing processes. To determine if sucrolytic and glycolytic enzyme expression increases to meet this demand and to identify the enzymes that may be induced, the activities of the major sucrolytic enzymes and the major regulatory enzymes of the glycolytic pathway were determined in wounded and unwounded sugarbeet roots during thirteen days of storage at 10o C. Activities of the enzymes responsible for catalysis of the first two reactions of the glycolytic pathway, hexokinase, fructokinase and phosphofructokinase, were elevated in wounded roots. The sucrolytic enzymes, sucrose synthase, alkaline invertase, and soluble acid invertase, and the glycolytic enzyme, pyruvate kinase, did not increase in wounded roots. The activities of the early glycolytic enzymes peaked 24 to 48 h after wounding when the demand for substrates for wound-healing processes was expected to be maximal. Fructokinase exhibited the greatest and most persistent increase in activity, increasing by 150% 24 h after wounding and remaining elevated for the duration of the study. The increase in hexokinase, fructokinase, and phosphofructokinase activities suggests that expression of these early glycolytic enzymes may be up-regulated to meet the demand for glycolytic intermediates and products for wound-healing processes. The lack of an increase in any sucrolytic activities in response to wounding suggests that sucrolytic flux is determined by a mechanism other than protein expression.