Abstract
Comparative enzymic studies of sugar beet (Beta vulgaris L.) taproots and fibrous roots revealed differences in invertase (EC 3.2.1.26) and sucrose synthetase (EC 2.4.1.13) activity. Invertase activity of the two root forms differs with respect to specific activity, pH optimum, and enzyme solubility. Acid invertase (pH 4.5) in the taproot was restricted to the peripheral meristematic tissue which produces cells for both taproot and fibrous root growth. This finding supports the hypothesis that the enzyme regulates sucrose partitioning between the taproot and fibrous roots. A distinct alkaline invertase (pH 8.0) was detected in sucrose storage tissues of the taproot.The V(max) of taproot sucrose synthetase (sucrose cleavage reaction) was highest in the presence of UDP. However, the fibrous root enzyme had the highest V(max) with ADP as substrate. Differential nucleoside diphosphate substrate affinities may provide for compartmentation and separate regulation of sucrose cleavage and resultant hexose utilization in adjoining taproot and fibrous root tissues.