Fructooligosaccharides changes during maturation in inflorescences and seeds of onion (Allium cepa L. ‘W202’)

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The distribution of fructooligosaccharides (FOS) and their related enzyme activities during the development of the inflorescences and the maturation of seeds in onion (Allium cepa L.) were investigated. Concentrations of glucose, fructose and sucrose in three inflorescence parts – complete floral parts (FP), pedicels (PD) and involucres (IV) - increased steadily during the first 8 wk of sampling and then decreased over for the next 6 wk. However the final glucose, fructose and sucrose contents were not significantly higher than those observed at the beginning of sampling. Surprisingly, FOS concentration in the inflorescence parts for the saccharides studied showed similar patterns with concentrations increasing during the first 6 wk and decreasing during the last 6 wk of the study. On the other hand, FL and PD parts contained higher amounts of FOS than IV parts. The activities of sucrose:sucrose 1-fructosyltransferase (SST), fructan: fructan 6G-fructosyltransferase (6G-FFT) and fructan:fructan 1F-fructosyltransferase (1-FFT) showed similar patterns in seeds, decreasing slowly during the first weeks and remaining stable thereafter. The ratio 6G-FFT to 1-FFT decreased after 9 wk from 2.40 to 1.44 with an average of 2.1. In contrast, activities of invertase and β-fructofuranosidase increased progressively, although β -fructofuranosidase activity was twice as high as invertase activity during the last 2 wk. The ratio of synthesizing to hydrolysing activities decreased progressively to 0.2 and was below the value 1 after 9 wk. Thus, it seems that seed maturation was reached during the last week of August, which is 2 to 3 wk earlier than seed harvest normally occurs in Hokkaido. Key words: Fructooligosaccharides, flower organs, seeds, onion