Differences in polymeric proteins among grains in spring wheat spikes

A uniform amount and size distribution of polymeric proteins within grains in a spike might determine the stability of wheat quality. Two cultivars were grown to maturity in solution culture in a climate chamber. Nitrogen (N) in the form of nitrate was added daily and replaced with N-15 before harvest. Plants were harvested during grain development. Protein composition and relationships of labelled N in grains from different spikelets within the spike were determined. Higher percentages of large unextractable polymeric proteins (%-LUPP) and total unextractable polymeric proteins (%-TUPP) were found in the lower- and uppermost spikelets in the spike compared with the middle ones for cv. WL, but not for cv. Sport. Both cultivars showed variations in the percentage of large unextractable monomeric proteins (%-LUMP) and total SDS-extractable protein (Tote) in the spikelets within the spike. The amount of total SDS-unextractable protein (Totu) did not vary for either of the cultivars. The spikelets within the spike showing high and low %-LUMP and Tote at maturity showed a similar behaviour shortly after flowering in cv. WL, but not in cv. Sport. The N concentration of SDS and sonicated extracts varied along the spikelets of the spike for both cultivars. The atom-% excess N-15 decreased in cv. Sport SDS-extractable and -unextractable proteins and cv. WL albumins + globulins, gliadins and glutenins from grains at different spikelet positions along the spike. (c) 2005 Society of Chemical Industry