The response of alpha-amylase activity during wheat grain development to nitrogen fertiliser

The aim of this study was to test whether the effect of nitrogen fertiliser on Hagberg falling number of winter wheat (Triticum aestivum) grain in the absence of sprouting is mediated by pre-maturity alpha-amylase activity and is related to grain drying rate. A field experiment with two cultivars (Avalon and Mercia) in 1990 and 1991 compared four application rates of nitrogen. Samples of grain were taken at intervals during development for moisture determination and alpha-amylase assay. Grains from plots given nitrogen dried faster in both years, but alpha-amylase activity and Hagberg falling number responded differently to nitrogen in the two years. In the warmer and drier year of 1990, alpha-amylase activity declined throughout development leading to very high Hagberg falling number at harvest, with little effect of nitrogen. In the cooler and wetter year of 1991, alpha-amylase activity declined until about 30% moisture. After this stage, alpha-amylase activity increased in the absence of sprouting in grain from plots receiving little or no nitrogen. This resulted in a linear increase in Hagberg falling number in response to nitrogen fertiliser. Electrophoresis of alpha-amylase isozymes indicated that the increase in Hagberg falling number in response to nitrogen was not mediated by a decrease in retained pericarp alpha-amylase activity, but by a reduction in pre-maturity alpha-amylase activity. These results support the hypothesis that slow grain drying enhances pre-maturity alpha-amylase formation, and also support the hypothesis that an additional environmental factor varying between seasons is involved in pre-maturity alpha-amylase formation.