Genetic basis and natural variation of α-amylase isozymes in barley

Abstract

Two physiologically and biochemically distinct groups of α-amylase (E.C.3.2.1.1) isozymes are synthesized when isolated aleurone layers of barley are incubated with gibberellic acid (GA3). Isoelectric focusing of the α-amylases showed that the isoelectric points of the isozymes of one group were near pH 5, whereas those of the second group were close to pH 6. Using wheat–barley addition lines, the genes for these groups were located in barley chromosomes 1 and 6 respectively. Joint segregation in the F2 generation of appropriate crosses indicated that the isozymes within each group were inherited collectively, and were attributed to codominant alleles segregating at two presumably complex loci, α-Amy 2 and α-Amy 1. The extent of genetic variation at these two loci was examined in 40 lines of Hordeum spontaneum (the wild progenitor of barley), and in a complex gene pool representative of H. vulgare (composite cross XXI). Variation at the α-Amy 1 locus was much more extensive than that at the α-Amy 2 locus. The genetic variation at both α-amylase loci exceeded that at the majority of other allozyme loci. However the α-amylase loci were less variable than the two loci coding for the seed storage protein, hordein. The wild species was found to contain much genetic diversity, which might be useful in modifying α-amylase activity by breeding. Parallels between the genetics and variation of α-amylase in barley and wheat were noted. © 1982, Cambridge University Press. All rights reserved.