SEASONAL FLUCTUATIONS IN FRUCTAN CONTENT AND RELATED ENZYME-ACTIVITIES IN YACON (POLYMNIA-SONCHIFOLIA)

The content of fructan and the activities of sucrose:sucrose fructan f ructosyltransferase (EC 2.4.1.99), fructan: fructan fructosyltransfera se (EC 2.4.1.100), and fructan hydrolase in each part of yacon (Polymn ia sonchifolia) were determined during the growth period. During summe r, the amount of fructan (g plant(-1)) accumulated in each part was mi nimal despite the existence of relatively high specific activities (un its mg(-1) protein) of sucrose:sucrose fructosyltransferase and fructa n: fructan fructosyltransferase in the stems, roots, tuberous roots, a nd rhizomataceous stem. On the other hand, from October to December, t he amount of fructan in the tuberous roots and rhizomataceous stem rem arkably increased along with an increase of the total activities (unit s plant(-1)) of sucrose: sucrose fructosyltransferase and fructan: fru ctan fructosyltransferase. The specific and total activity of fructan hydrolase in each part markedly increased in September when the rapid regrowth of aerial parts after physical damage caused by strong typhoo n winds was observed. In this month, the amount of fructan in the tube rous roots and rhizomataceous stem decreased. The specific and total a ctivity of fructan hydrolase in the tuberous roots increased again in December while at the same time there was a decrease in the content of fructan and an increase in the content of fructose.