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Depolymerization of the Glutenin Macropolymer During Mixing: II. Differences in Retention of Specific Glutenin Subunits

¹CSIRO Plant Industry and Quality Wheat CRC Ltd., G.P.O. Box 1600, Canberra, ACT 2601 Australia. ²Corresponding author. Fax +61 2 6246 5351/5000. E-mail: J.Skerritt@pi.csiro.au ³CSIRO Plant Industry and Quality Wheat Cooperative Research Centre Ltd., P.O. Box 7, North Ryde, NSW 2113 Australia.

The depolymerization of individual high and low molecular weight (HMW and LMW, respectively) glutenin subunits (GS) from the glutenin macropolymer (GMP) in doughs during mixing was investigated by reversed-phase (RP) HPLC and SDS-PAGE. Cultivars with different dough strengths, as well as lines null for specific HMW-GS and biotypes differing at individual HMW-GS and LMW-GS encoding loci, were studied. During mixing, the proportion of total HMW-GS in GMP decreased, and the ratios of different subunits in the GMP in doughs changed. There was a loss of chromosome 1B- and 1D-encoded x-HMW-GS, while the relative proportions of y-HMW-GS (among HMW-GS) increased. Changes in 1B subunits occurred first, while most of the changes in 1D HMW-GS content occurred during dough breakdown. Changes were more pronounced for doughs of weak to average strengths than for stronger doughs. RP-HPLC analysis demonstrated a consistent increase in the retention times (surface hydrophobicity) of chromosome 1D-encoded HMW-GS but not of other HMW-GS or LMW-GS during mixing. SDS-PAGE and RP-HPLC demonstrated that specific B subunits, typically those with lower hydrophobicity, were selectively depolymerized from the GMP during dough breakdown, while the proportions of specific C subunits, typically those with greater hydrophobicity, increased. Similar trends were seen in analyses of several pairs of biotypes differing at single LMW-GS encoding loci, although there were slight differences in the depolymerization behavior of wheats with different allelic compositions. The results suggest that dough breakdown may be triggered by the loss of specific HMW-GS from the GMP, and a structural hierarchy may exist for different LMW-GS within glutenin in doughs.