The accumulation of fructo-oligosaccharides and the activities of
fructosyltransferase (sucrose[ratio ]sucrose 1F-fructosyltransferase
(SST), 1F-fructosyltransferase (1F-FT)
and 6G-fructosyltransferase (6G-FT)) in the bulbs of
three onion cultivars were investigated from June to September 1993. The total
fructo-oligosaccharide content
increased from June until August, then decreased in September, except in
one cultivar. The levels of neokestose
and its related tetrasaccharides
(1F, 6G-di-β-D-fructofuranosyl sucrose and
6G (1-β-D-fructofuranosyl)2sucrose) were
higher than those of 1-kestose and nystose throughout growth. The activities of
6G-FT, 1F -FT and SST were high
in June and July, then decreased; SST activity was very low in September. The
activity ratios of 6G-FT to 1F-FT varied between
1·86 and 2·65 over the growth period. Two trisaccharides, three
tetrasaccharides and four
pentasaccharides were identified, together with a mixture of hexa- and
heptasaccharides, all of which were
synthesized in vitro from 0·1 M sucrose by an
enzyme preparation of onion bulbs harvested in August. Octa- and
nonasaccharides other than the saccharides formed from sucrose were also
synthesized from 0·1 M 1-kestose or
0·1 M neokestose. All the saccharides produced from sucrose,
1-kestose or neokestose by the crude enzyme
prepared from onion bulbs were identical to the saccharides occurring
naturally in onion bulbs.