Changes of enzyme activities associated with the mobilization of carbohydrate reserves (fructans) from the stem of wheat during kernel filling

Abstract

(This paper is dedicated to Professor Ludwig Bergmann on the occasion of his 70th birthday) Wheat plants were grown at a day\night temperature of 18\13 mC under glasshouse conditions. Twenty-two d after anthesis, one set of plants was shaded to 50 % of the normal photon fluence rate, another was ' degrained ' by selective spikelet removal which left only the grains in the five central spikelets ; a further set was left as control. Individual plants were harvested at days 22, 30 or 42 after anthesis. Extracts from the peduncle and the penultimate internode were prepared to determine the activities of sucrose phosphate synthase, sucrose synthase, fructan exohydrolase and acid invertase, and to assess the concentration of hexose sugars, sucrose and fructans. Measurements were also made of ear and individual grain weights, and stem f. wt and d. wt. There was a decline in the amount of fructans with time, more pronounced in ' shaded ' (source-limited) than in control plants. By contrast, in ' degrained ' (sink-limited) plants, the amount of fructans in the stem initially rose, then decreased, with a concomitant increase in the amount of fructose. The shifts in sugar content of the wheat culm reflected both the sink demand of the ear and source activity. The activity of fructan exohydrolase correlated with the carbohydrate changes. Under limited photosynthate assimilation, the mobilization of fructans from the internodes towards the ear was related to an increase in this enzyme, whereas the other enzymes played a less direct role in the mobilization of fructan reserves from the wheat stem.

Molecular Dissection of Variation in Carbohydrate Metabolism Related to Water-Soluble Carbohydrate Accumulation in Stems of Wheat

“…WSCs can accumulate in wheat stems to more than 40% of total stem dry weight (McCaig and Clarke, 1982;Blacklow et al, 1984;Housley, 2000). WSCs mobilize from the stem during the later phase of grain filling (Willenbrink et al, 1998) and can potentially contribute to about 20% of grain yield under normal conditions (Schnyder, 1993;Blum, 1998;Wardlaw and Willenbrink, 2000). A similar level of stem WSC contribution to grain yield has been shown in barley (Bingham et al, 2007).…”

Spring Cereals: From Dynamic Ideotypes to Cultivars in Northern Latitudes

“…Modern wheat cultivars have the ability to utilise remobilisable assimilates produced before and after anthesis for grain filling to maintain grain weight (Pheloung and Siddique 1991). This is shown as a loss of dry weight in the upper two internodes (Davidson and Chevalier 1992), culms (Willenbrink et al 1998) and the uppermost pulvinus (Virgona and Barlow 1991) simultaneously with an increase in grain weight. Usually the carbohydrates stored as fructans having a degree of polymerization between three and eight in stems are utilised as buffers of fluctuations in carbohydrate production (Kühbauch and Thome 1989).…”

Mobilization of fructan reserves and changes in enzyme activities in wheat stems correlate with water stress during kernel filling

“…The final concentration of sucrose should easily saturate the reaction with INV, which is commonly found to have a K m in the range 2-13 mM (Avigad, 1982). For the FEH assay fructan extracted from Lolium rigidum was used as substrate (Willenbrink et al, 1998). The fructans extracted from L. rigidum used here, although having a greater degree of polymerization than those found in the stem of wheat, are similar in that they have a predominance of β-2, 6-glycosidic linkages (Bonnett & Simpson, 1995).…”

“…The enzymes for this conversion were not analysed in this study. In an earlier study (Willenbrink et al, 1998), shading the culm of wheat (cv. Lyallpur) during kernel filling enhanced the mobilization of the stem reserves and there was a corresponding increase in FEH activity.…”