Studies on the physiology and enzymology of fructosan utilization in the tuber of Helianthus tuberosus L

• Main Author: Jefford, Timothy George
• Published: Imperial College London 1963
• Subjects: 635; Jerusalem artichoke
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602225

It is shown that polymerized fructose present in tubers of Helianthus tuberosus L. is utilized in the growth of new plants; over a few weeks, tubers lost 8O% of their dry weight, fructose accounting for 8O% of this loss. The translocation of material from the tuber was accompanied by depolymerization of fructosan; this was consistent with the assumption that carbohydrate was transported in the form of sucrose. Depolymerization did not occur in tubers at 20°C which were not translocating material, but could be induced in dormant tubers by storage at low temperature (2-8°C). The mechanism of depolymerization in both these circumstances Was examined, and it is shown to be the same in each case; the evidence is consistent with the hypothesis that the first stage in the process is the liberation of free fructose from the fructosan. Two enzymes which catalyse the hydrolysis of fructosans found in the artichoke tuber were separated from tuber extracts. Their specificity appeared to be confined to the hydrolysis of the beta2-1 linkage between a terminal fructose and its adjacent residue, but in addition, the rate at which a particular sugar was attacked depended to a large extent on the number of residues it contained. The characteristics of one of these enzymes were investigated in detail, with particular reference to its possible role in the living plant: no properties were found which would preclude its being active in vivo; an important feature was found to he inhibition by sucrose which could represent a possible factor in the control of fructosan breakdown.