Fructans polymerised and depolymerised in the internodes of winter wheat as grain-filling progressed

Carbohydrates soluble in 70% (v/v) ethanol were the major causes of the changes in the dry matter of the three internodes below the peduncle of a crop of winter wheat grown in Yorkshire, U.K. The concentration of soluble carbohydrates reached a maximum 24 days after anthesis when they were 42% of the dry matter and declined to 3% at grain maturity. Gel permeation chromatography was used to separate the polymers of fructose and there was little indication that the maximum degree of polymerisation was greater than 9 (DP9). Fructans of $\text{DP}\text{≧ 5}$ increased rapidly to a maximum concentration of 27% at 24 days while those of DP(3+4) reached a maximum concentration of 9% about 10 days after anthesis. Sucrose, fructose and glucose, in that order, were at lower concentrations in the internodes than the fructans. Polymerisation followed by depolymerisation was explained by the changing balance between net photosynthesis and rates of grain growth. Nitrogen nutrition of the crop had little effect on the quantitative and qualitative changes in the soluble carbohydrates of the internodes.