Fructan metabolism in developing wheat (Triticum aestivum L.) kernels

Although fructans play a crucial role in wheat kernel development,their metabolism during kernel maturation is farfrom being understood. In this study, all major fructanmetabolizingenzymes together with fructan content, fructandegree of polymerization and the presence of fructanoligosaccharides were examined in developing wheat kernels(Triticum aestivum L. var. Homeros) from anthesis until maturity.Fructan accumulation occurred mainly in the first2 weeks after anthesis, and a maximal fructan concentrationof 2.5 ± 0.3 mg fructan per kernel was reached at 16 daysafter anthesis (DAA). Fructan synthesis was catalyzed by1-SST (sucrose:sucrose 1-fructosyltransferase) and 6-SFT(sucrose:fructan 6-fructosyltransferase), and to a lesserextent by 1-FFT (fructan:fructan 1-fructosyltransferase).Despite the presence of 6G-kestotriose in wheat kernel extracts,the measured 6G-FFT (fructan:fructan 6G-fructosyltransferase)activity levels were low. During kernel filling,which lasted from 2 to 6 weeks after anthesis, kernel fructancontent decreased from 2.5 ± 0.3 to 1.31 ± 0.12 mg fructanper kernel (42 DAA) and the average fructan degree of polymerizationdecreased from 7.3 ± 0.4 (14 DAA) to 4.4 ± 0.1(42 DAA). FEH (fructan exohydrolase) reached maximalactivity between 20 and 28 DAA. No fructan-metabolizingenzyme activities were registered during the final phase ofkernel maturation, and fructan content and structureremained unchanged. This study provides insight into thecomplex metabolism of fructans during wheat kernel developmentand relates fructan turnover to the general phasesof kernel development.