Free sugars and their relationship with grain size and starch content in developing wheat grains

Abstract

Free sugars in wheat varieties, at different stages of grain development and differing in grain size and starch content per grain, were analysed to determine any relationship with grain size and starch content. Fresh and dry weight (mg per grain) of developing grain increased with maturity until 35 days after anthesis. Fresh weight declined after 35 days but dry weight remained almost constant. Water content increased until the 21 and/or 28 day stage and then decreased. Active starch synthesis started from 14 days onwards and continued until 35 days after anthesis. Free sugars (total sugars, reducing sugars, non-reducing sugars and sucrose) per grain followed closely the changes in the rate of starch accumulation and, in general, were maximum at the 14 day stage followed by a decline up to 28 days, with no significant alteration afterwards. Presence of adequate amounts of soluble sugars in grain even when starch synthesis had stopped suggested that the supply of sugar precursors did not limit starch synthesis. None of the sugars was found to have a significant relationship with either grain size or starch content. A hypothesis explaining the termination of starch accumulation in developing cereal grains has been proposed.