Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2000
Publication Date: N/A
Technical Abstract: Three enzyme activities are responsible for nearly all sucrose catabolism in sugarbeet roots. Acid invertase, alkaline invertase and sucrose synthase activities convert sucrose to hexose sugars providing substrates for cellular metabolism and biosynthesis of cellular structures. A single soluble acid invertase isoenzyme and two alkaline invertase isoenzymes were evident in sugarbeet roots. A cell wall acid invertase activity was also present but was not characterized due to the inability to extract this activity from the cell wall. Two sucrose synthase isoenzymes were also present. In greenhouse grown sugarbeets, the soluble acid invertase isoenzyme was the predominant sucrolytic activity in seedling roots. Acid invertase activity declined precipitously after two weeks of growth and was barely detectable by six weeks of age. Two alkaline invertase isoenzymes were present at all stages of development at low levels. Although total alkaline invertase activity was relatively constant during root growth, the individual contribution of the two isoenzymes changed with development. The predominant sucrolytic activity in sugarbeet roots at all but the earliest stages of development was sucrose synthase. By four weeks, sucrose synthase was the major sucrose catabolizing enzyme in sugarbeet roots and remained the major sucrolytic activity at all subsequent stages of development. One sucrose synthase isoenzyme was present during the first twelve weeks of growth. Two isoenzymes were present at sixteen weeks. These studies suggest that sucrose synthase is largely responsible for sucrose catabolism and the provision of metabolic intermediates during all but the earliest stages of root growth.