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Bulk Carbohydrate Grain Filling of Barley β-Glucan Mutants Studied by ¹H HR MAS NMR

¹University of Aarhus, Faculty of Agricultural Sciences, Dept. of Genetics and Biotechnology, Forsøgsvej 1, 4200 Slagelse, Denmark. ²University of Copenhagen, Faculty of Life Sciences, Dept. of Food Science, Quality & Technology, Rolighedsvej 30, 1958 Frederiksberg C, Denmark. ³Corresponding author. Phone: +45 3533 3205. Fax: +45 3533 3245. E-mail: se@life.ku.dk

Temporal and genotypic differences in bulk carbohydrate accumulation in three barley genotypes differing in the content of mixed linkage β-(1→3),(1→4)-D-glucan (β-glucan) and starch were investigated using proton high-resolution, magic angle spinning, nuclear magnetic resonance (¹H HR MAS NMR) during grain filling. For the first time, ¹H HR MAS NMR spectra of flour from immature barley seeds are analyzed. Spectral assignments are made using two-dimensional (2D) NMR methods. Both α- and β-glucan biosynthesis were characterized by inspection of the spectra as well as by calibration to the reference methods for starch and β-glucan content. Starch was quantified with very good calibrations to the α-(1→4) peak (5.29–5.40 ppm) and the region 3.67–3.83 ppm covering starch glycopyranosidic protons from H5 and H6. In contrast, the spectral inspection of the β-anomeric region 4.45–4.85 ppm showed unexpected lack of intensity in the high β-glucan mutant lys5f at seed maturity, resulting in poor calibration to reference β-glucan content. We hypothesize that the lack of β-glucan signal in lys5f indicates partial immobilization of the β-glucan that appears to be either genotypic dependent or water/β-glucan ratio dependent.