New Data Supporting High Mr Glutenin Subunit 5 as the Determinant of Quality Differences among the Pairs 5 + 10 vs. 2 + 12

One- and two-dimensional electrophoretic separations were performed on high Mr subunits of glutenin of the bread wheat cultivar Fiorello, which was reported to possess the recombinant 5 + 12 subunits at the Glu-D1 locus. Comparison with results for the bread wheat cultivar Cheyenne, possessing the pair 5 + 10, indicated that subunit 5 of Fiorello was different, both in size and isoelectric point, from subunit 5 of Cheyenne. RP-HPLC separations of high Mr glutenin subunits also indicated that the two types of subunit 5 were different in surface hydrophobicity. The sequence of a cloned DNA fragment isolated from Fiorello, corresponding to the N-terminal part of the protein, indicated the absence of the additional cysteine residue at the beginning of the repetitive domain flanking the N-terminal region typical of subunit 5. The data show that the Dx subunit of Fiorello, indicated as 5*, is more similar to subunit 2 than to subunit 5, raising doubts on previous results excluding subunit 5 as being responsible for the differences in breadmaking quality observed in the pairs 5 + 10/2 + 12.