Fructan Accumulation and Sucrose:sucrose Fructosyltransferase Activity in Stems of Spring Wheat Genotypes

Stems of wheat (Triticum aestivum L.) accumulate water‐soluble carbohydrates (WSC) during the first 3 wk after anthesis. These reserves can later contribute to grain filling. Two spring wheat genotypes (‘Kolibri’ and breeding line D) were tested in growth chambers to determine if they differ in the accumulation of WSC components and in the activation of sucrose:sucrose fructosyltransferase (SST) in stem tissue. Concentration of CO2 was supplied at 1000 or 300 μL CO2 L−1 after anthesis to alter photosynthate production. The WSC accumulation in the penultimate internode during the first 18 d post anthesis (DPA) was substantially higher in Genotype D than in Kolibri. The WSC accumulation up to 7 DPA was due to increases in hexoses and sucrose. Sucrose concentration was initially lower in Kolibri than in Genotype D, but increased to a comparable level for both genotypes and both CO2 treatments. Fructan synthesis was initiated at 7 DPA. At 18 DPA, fructan was the dominant component of WSC. Under both CO2, treatments Genotype D accumulated substantially higher fructan concentrations than Kolibri. In a second experiment, induction of SST activity was observed during the first 9 DPA in the penultimate internode of plants grown at 1000 and 200 μL CO, L−1. There was a positive relationship between sucrose concentration and in vivo SST activity, suggesting that sucrose induced SST activity; however, Kolibri exhibited a much lower SST activity at given sucrose concentration. Thus, the low fructan synthesis of Kolibri is associated with an initial lower sucrose concentration and with a less effective activation of SST by sucrose.