Differential effects of Wx-A1,-B1 and-D1 protein deficiencies on apparent amylose content and starch pasting properties in common wheat

Waxy (Wx) protein is a granule-bound starch synthase (GBSS) responsible for amylose production in cereal endosperm. Eight isolines of wheat (Triticum aestivum L.) having different combinations of presence and absence of three Wx proteins, Wx-A1, -B1, and -D1, were produced in order to elucidate the effect of Wx protein deficiencies on the apparent amylose content and starc h-pasting properties. An improved SDS gel electrophoresis showed that 'Bai Hue' (a parental wheat) carried a variant Wx-B1 protein from an allele, Wx- B1e. Thus, wheat lines of types 1, 2, 4, and 6 examined in this study conta ined a variant Wx-B1 allele and not the standard allele, Wx-B1a. The result s from 3 years of experiments using 176 lines derived from two cross-combin ations showed that apparent amylose content increased the least in type 8 ( waxy) having no Wx proteins and, in ascending order, increased in type 5 (o nly the Wx-A1 protein is present) <type 7 (Wx-D1) <type 6 (Wx-B1) <type 3 ( Wx-A1 and -D1) <type 4 (Wx-A1 and -B1) <type 2 (Wx-B1 and -D1) <type 1 (thr ee Wx proteins). However, Tukey's studentized range test did not detect sig nificant differences in some cases. Densitometric analysis suggested that t he amylose content was related to the amount of the Wx protein in the eight types. Parameters in the Rapid Visco-Analyzer test and swelling power were correlated to amylose content. Consequently, amylose content and pasting p roperties of starch were determined to be influenced the most by the lack o f the Wx-B1 protein, followed by a lack of Wx-D1, and leastly by the Wx-A1 deficiency, which indicated the presence of differential effects of the thr ee null alleles for the Wx protein.