Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 4, 2001
Publication Date: N/A
Interpretive Summary: The two macromolecules that comprise starch in wheat flour, namely amylose and amylopectin, are chemically very similar. However, the linear (amylose) vs. branched (amylopectin) nature of these macromolecules causes a difference in the processing and functional characteristics of their wheat flours. The synthesis of amylose is thought to be exclusively controlled by an enzyme called granule bound starch synthase (GBSS). Because of modern (hexaploid) wheat's ancestry, the production of GBSS is regulated by three genes, with each originating from a separate genome. Most commercial varieties possess all three genes in an active state. Only when all three genes are inactive (that is, are null alleles) does the production of GBSS and hence, synthesis of amylose, become nil. Currently, wheat breeding programs are underway in the United States and elsewhere to develop waxy (zero amylose) and partial waxy (low amylose) varieties for use in the production of modified starch, Asian noodles, paper, and adhesives. The current study was undertaken to examine the possibility of using near-infrared (NIR) spectroscopy, a technique in common use in the cereals industry, to distinguish waxy (0 active GBSS genes) from partial waxy (1-2 active) from wild-type (all 3 active). Approximately 200 wheat lines replicated over two years were tested. NIR discriminant analysis models indicate that identification of waxy lines was accomplished with near-perfect accuracy. More difficult was the separation of partial waxy from wild-type lines. The immediate beneficiary of this work is the plant breeder. As waxy wheat varieties eventually become released, this method will allow growers, traders, and processors to easily authenticate this attribute of added value.
Technical Abstract: Newly developed low amylose wheats have unique processing characteristics, and thus allow millers to blend defined levels of amylose in mixes requiring low-amylose flour. The amount of amylose synthesized during grain fill is dependent on the expression of three structural genes that encode isoforms of granule-bound starch synthase (GBSS). Lines possessing all three fully functional waxy loci produce the highest proportion of amylose to amylopectin, while those with one or more null alleles produce successively smaller proportions. Conventional methods for determining the number of active starch synthase genes or isoforms, such as SDS-PAGE, are difficult and time consuming. The present study was undertaken to determine the feasibility of using near-infrared (NIR) spectroscopy to classify wheat by the number of active GBSS genes. Nearly 200 lines from each of two harvest years, with a range of zero (waxy) to three (wild type) active genes, were ground and scanned (1100-2500 nm) in NIR reflectance. Linear or quadratic discriminant functions of the scores from principal component decomposition cross validation demonstrated that perfect separation of fully waxy lines was achievable. Partial waxy (one or two active genes) and wild type lines were classified at approximately 60% accuracy. Misclassifications were most often assignments into neighboring gene classes (e.g., 1-gene line assigned to the 2-gene class). The most probable spectral basis of GBSS classification by NIR is sensitivity to the amylose concentration.