ACCUMULATION OF PROTEIN SUBUNITS AND THEIR POLYMERS IN DEVELOPING GRAINS OF HEXAPLOID WHEATS

Technological properties of wheat flours are largely governed by the f unctional properties of storage proteins, comprising single chain glia dins and disulphide-bonded polymeric proteins (glutenins, triticins, H MW albumins), This study was conducted (a) to measure the rate of accu mulation of different classes of proteins, (b) to monitor the rate of polymerization of the polymeric subunits, and (c) to investigate the o rigin of differences in the degree of polymerization arising from alle lic differences at the Glu-D1 locus of HMW glutenin subunits. Developi ng grains from hexaploid wheat cultivars were collected at 3-d interva ls between 7 d and 40 d after anthesis (DAA). The accumulation behavio ur of polymeric proteins was determined by size exclusion-HPLC and of the constituent polypeptides (HMW glutenin subunits, LMW glutenin subu nits, HMW albumin subunits) by a combination of SDS-PAGE, reversed pha se-HPLC and immunoblotting, The relative time for peak accumulation of the albumins/gobulins, gliadins and polymeric proteins occurred in th at order during grain filling. Deposition of HMW glutenin subunits, LM W glutenin subunits and HMW albumin subunits (beta-amylases) began as early as 7 d after anthesis and progressed until maturity, Disulphide- linked aggregation (polymerization) of these subunits also commenced a t 7 DAA. However, significant changes in size distribution of the poly mers occurred only during the late stages of seed development which co incided with a rapid increase in the amounts of the glutenin subunits, The effects of HMW albumin subunits and LMW glutenin subunits on poly mer size were relatively smaller than that of the HMW glutenin subunit s. The wheat biotype with HMW glutenin subunits 5+10 (Glu-D1d allele) accumulated larger polymers more quickly than the biotype with allelic subunits 2+12 (Glu-D1a allele), this difference becoming apparent at 28 DAA which could be attributed to variation in the accumulation rate of HMW glutenin subunits.