IDENTIFICATION AND CHARACTERIZATION OF US WHEATS CARRYING NULL ALLELES AT THE WX LOCI

Granule-bound starch synthase (GBSS) is the primary enzyme responsible for the synthesis of amylose in amyloplasts of cereal endosperm cells . Bread wheats, due to their hexaploid genetic system, carry three gen es (wx loci) encoding GBSS. Purification and separation of GBSS from m ore than 200 North American hexaploid wheats allowed the identificatio n of genotypes that carry null alleles at either the wx-Al and wx-Bl l oci. In addition, the cultivar Ike carried both wx-Al and wx-Bl null a lleles. No wx-Dl nulls were detected. Null alleles were found in 10% o f the hard winter wheats tested, but in only 2% of the sampled soft wi nter wheats. Amylose contents of wheats carrying single null alleles a t either the wx-Al or rr?x-BI loci often were lower than those of wild type wheats, but greater reduction in amylose content was observed in Ike. Monoclonal antibodies were used to quantify water-extractable GB SS in both wild-type and null genotypes. Gene dosage compensation was evident, although GBSS content, as measured by ELISA, was significantl y lower in Ike than in all other wheats. The identification of null al leles in adapted genotypes suggests the development of wheats with a w ide range of amylose contents will be possible by simple genetic cross ing and selection.