Abscisic acid associated with key enzymes and genes involving in dynamic flux of water soluble carbohydrates in wheat peduncle under terminal drought stress.

Remobilization of stem water soluble carbohydrates (WSC) can supply crucial carbon resources for grain filling under drought stress, while the regulatory metabolism associated with abscisic acid (ABA) is still limited. Two cultivars, LJ196 (drought-tolerant) and XD18 (drought-prone), were pot-grown under well-watered (WW) and drought-stressed (DS) conditions. Concentrations of WSC components and ABA, and fructan metabolizing enzymes and genes were investigated in peduncle after anthesis. When compared with those under the WW, LJ196 remained higher grain yield and grain-filling rate than XD18 under the DS. During the early period of grain filling (0-14 DAA), DS increased concentrations of total WSC and its components, but thereafter substantially reduced them. The gene expression levels and enzymatic activities of fructan 1-exohydrolases (1-FEH) and fructan 6-exohydrolases (6-FEH) showed similar trends, whereas those of fructan: fructan 1-fructosyltransferase (1-FFT), and sucrose: fructan 6-fructosyltransferase (6-SFT) were depressed and declined over the period of examination. LJ196 still showed higher levels of ABA and fructan metabolizing. The ABA concentration under the DS was positively and significantly correlated with total WSC and fructan concentration, and expression levels of these enzymes and genes as well, with more prominently with those of 6-FEH. Presumably, ABA could enhance fructan hydrolysis by strongly up-regulating the gene expression and enzymatic activity of 6-FEH to accelerate WSC remobilization. However, stem WSC induced by DS could be not fully remobilized to grains, due to its weaker correlation with grain-filling rate and finally indicating lower grain yield. The findings would provide useful information for wheat production under water-deficit environments.