STORAGE AND REMOBILIZATION OF WATER-SOLUBLE CARBOHYDRATES IN STEMS OF SPRING WHEAT

Grain yield of wheat (Triticum aestivum L.) depends, in part, on carbohydrate reserves available in the stem. This study conducted to determine the effects of water deficit during the post-jointing period on quantitative changes in water soluble carbohydrates (WSC; including simple sugars, starch, and fructans) in the stems of spring wheat. Cultivars Edwall and Waverly were planted in 1983 and 1984 at Spillman Agronomy Farm near Pullman, WA, at rates of 84 and 168 kg ha-1 in rows 30 and 15 cm apart, respectively, in both irrigated and nonirrigated treatments. Beginning at jointing, plants were harvested weekly. Stem material was dried, milled, digested with amyloglucosidase, and analyzed for WSC by iodometric titration. Results were similar for both varieties and both years. Anthesis and peak stem carbohydrate concentration occurred 4 to 7 d earlier in nonirrigated than irrigated plants; and physiological maturity of the grain occurred 6 to 14 days earlier. The concentration of WSC in stems increased to between 250 and 380 mg g-1 dry wt. at almost-equal-to 10 to 14 d after anthesis and then declined to less than 50 mg g-1 dry wt. by physiological maturity of the grain. From the time of peak WSC content until physiological maturity in 1984, 859 to 1235 mg WSC were lost from the stems of irrigated plants but only 619 to 662 mg WSC were lost from stems of nonirrigated plants. The data indicate that stems are an important temporary storage site for reserve carbohydrates in both irrigated and nonirrigated plants.