1) Three fructofuranosidases were separated by chromatography on DEAE-cellulose columns from the soluble protein extracted from dandelion (Taraxacum officinale Weber) roots. One enzyme, which acted on sucrose, was characterized as an invertase, with a Km of 2.00x10-2M and pH optimum of 7.5. The other two enzymes are hydrolases (A and B) which act on the inulin series of carbohydrates, general formula: [glucose-fructose-(fructose)n], to release single fructose residues. They both have a pH optimum of 4.0 and Km of 1.54x10-2M but differ in their chromatographic behaviour on DEAE-cellulose, 2) Soluble protein extracts prepared from dandelion roots were able to synthesise oligosaccharides from sucrose by transfructosylation. Preliminary experiments suggest that this occurs via two enzymes; SST (pH optimum 4.5) catalysing the formation of 1F-fructosylsucrose from sucrose, the other, FFT (pHoptimum 8.5) catalyses the formation of higher oligosaccharides from 1F-fructosylsucrose. 3) Treatment of tissue disks prepared from dandelion roots with solutions of the highly active growth regulator 2, 4-dichlorophenoxyacetic acid (2,4-D) resulted in a large uptake of water. This was accompanied by an increase in hydrolase activity and depolymerization of the storage carbohydrate inulin; the free sugars released did not accumulate but were immediately utilized by the tissue. The net result was an increase in the rate of respiration and the depletion of carbohydrate reserves. The increase in hydrolase activity was inhibited by actinomycin D, indicating that the synthesis of a messenger RNA is involved. The increase in hydrolase activity was also inhibited if various sugars were included in the incubation medium. Similar treatment with the isomer 3,5-dichlorophenoxyacetic acid (3,5-D) which is inactive as an auxin, produced little or no response, and was even able to inhibit the action of 2,4-D. 4) In the summer, flowering of dandelion plants was accompanied by depletion of carbohydrate reserves present in the roots; these reserves were restored in the autumn. The variations in hydrolase and transfructosylase activities were consistent with these changes. The response of tissue disks to treatment with 2,4-D showed a similar seasonal variation to that of the initial fructosan content, suggesting that the availability of carbohydrate reserves limits the response throughout the season.
|Date of Award||1973|