EFFECTS ON THE STEM OF WINTER BARLEY OF MANIPULATING THE SOURCE AND SINK DURING GRAIN-FILLING .2. CHANGES IN THE COMPOSITION OF WATER-SOLUBLE CARBOHYDRATES OF INTERNODES

Field-grown barley plants were manipulated by removing ears and by shading to promote an to reduce, respectively, the storage of carbohydrates in their stems. Water-soluble carbohydrate (WSC) was extracted and separated by HPLC into glucose, fructose, sucrose, and fructan of degree of polymerization (DP) 3, 4, 5, > 5, and measured in both the penultimate and fourth internodes from the ear to determine the effects of the manipulations. During the accumulation of WSC, the mass of fructan with a DP greater than 5 continued to increase whilst the mass of fructans of DP 3 to 5 reached a maximum and then remained constant. Fructan accumulated in internodes while they were extending although most of the fructan in an internode accumulated after it was fully extended. When WSC was mobilized from the stem, the mass of glucose, sucrose and fructan decreased but the mass of fructose first increased then decreased, indicating that fructan was hydrolysed at a faster rate than its product, fructose, could be utilized. Plants shaded to 50% of incident light from 14 d after anthesis accumulated the same mass of WSC in the stem as control plants in one crop, whereas in another crop, plants shaded to 9% of incident light from 11 d after anthesis accumulated less WSC than control plants. WSC in the stem was lost from the more intensely shaded plants earlier than from control plants. Plants de-cared at anthesis and at 21 d after anthesis accumulated a similar mass of WSC to control plants, although plants de-eared at 9 d after anthesis, in another crop, accumulated a greater mass of WSC than control plants. Although control plants mobilized almost all of their stored WSC, de-eared plants retained 43 55% of the WSC stored in their penultimate internode and did not lose any stored WSC from their fourth internode. In the penultimate internodes of de-eared plants the mass of glucose, sucrose and fructan decreased and this was balanced in part by an increase in the mass of fructose. In the fourth internode, the mass of WSC remained constant but the mass of accumulated fructose was equal to the decrease in the mass of fructan. Results are discussed in relation to current knowledge of fructan metabolism and to contributions of stored WSC to grain yield.