Seasonal fluctuations in fructan content and related enzyme activities in yacon (Polymnia sonchifolia)

The content of fructan and the activities of sucrose: sucrose fructan fructosyltransferase (EC 2.4.1.99), fructan: fructan fructosyltransferase (EC 2.4.1.100), and fructan hydrolase in each part of yacon (Polymnia sonchifolia) were determined during the growth period. During summer, the amount of fructan (g plant−1) accumulated in each part was minimal despite the existence of relatively high specific activities (units mg−1 protein) of sucrose: sucrose fructosyltransferase and fructan: fructan fructosyltransferase in the stems, roots, tuberous roots, and rhizo-mataceous stem. On the other hand, from October to December, the amount of fructan in the tuberous roots and rhizomataceous stem remarkably increased along with an increase of the total activities (units plant−1) of sucrose: sucrose fructosyltransferase and fructan: fructan 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 typhoon winds was observed. In this month, the amount of fructan in the tuberous roots and rhizomataceous stem decreased. The specific and total activity 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.