Beta-Glucans Deposition in Malting Barley As Affected by Nitrogen Supply.

Beta-glucans are cell-wall polysaccharides typically concentrated in aleurone and sub-aleurone layers of endosperm in barley, rice and oats. Beta-glucans can reduce extract yields in the brewhouse and cause poor filtration during mashing. New information on β-glucans deposition in developing kernels can assist breeders in designing new malting barley materials. Three field experiments were run in Udine (NE Italy) on a shallow soil (Chromi-Skeletic Cambisol; FAO, 1998). A total of 6 barley varieties were  fertilized with 0, 50, 100, 150 kg N ha^-1 (ammonium nitrate) in a split-plot design with cultivars in sub-plots and three reps.  A portable chlorophyll reader (SPAD 502 Minolta®) was used in top-canopy leaves to assess crop N status.  Throughout reproductive stages, total nitrogen (NA-1500 Elemental Analyzer, Carlo Erba, Italy) and β-glucans (McCleary Streamlined Method, Megazyme®, Ireland) concentrations were measured in 30-40 developing kernels taken from 10-12 heads per plot. At maturity (GS 92, Zadoks) total aboveground biomass was determined and crop N uptake calculated. Substantial differences across years were observed for grain yield and kernels m^-2. Crop  sinks size could play a role in β-glucans levels and deposition.  In one out  of  three experiments, a two-stage model was apparently in place: β-glucans increased linearly with slopes roughly proportional to N level, then separate plateaux were observed.  Conversely, a different model  with no separate plateaux was obtained in other experiments. Crop sinks size, possibly  through variation of  the cell wall total volume, could be a factor for β-glucans deposition in barley endosperm.