RESUMEN
BACKGROUND: Lipoxygenases are a family of enzymes which catalyse the hydroperoxidation of polyunsaturated fatty acids with a cis, cis-1,4-pentadiene to form conjugated hydroperoxydienes. Lipoxygenase-1 (LOX-1) in barley worsens the flavour and foam stability of beer. It has become a major selection criteria for malting quality in the last few years. RESULTS: Lipoxygenase activity was investigated in 41 Australian barley cultivars and advanced breeding lines released since the 1950s; the cultivars differed markedly, ranging from 22.3 to 46.5 U/g. The structural gene and its promoter of lipoxygenase-1 were sequenced from the barley varieties representing different levels of LOX. Based on the analysis of nucleotide and deduced amino acid sequences, two major haplotypes were identified. Barley varieties with lower LOX were classified into three categories based on their pedigrees and sequence variations in the structural gene: (1) barley varieties derived from Canadian varieties with the pre-harvest sprouting susceptible allele, (2) Skiff and Hindmarsh with unique haplotype in the structural gene, and (3) Gairdner and Onslow with an unknown mechanism. CONCLUSION: Lipoxygenase activity has been reduced in the malting barley cultivars in the last 60 years although it is only recognized as a malting quality trait recently. There are clear haplotypes of the lipoxygenase structual gene. The polymorphisms detected in the structural gene can be used to design molecular markers for selection of low LOX haplotype. Other mechanisms also existed for controlling lipoxygenase activity. The results suggest that it is possible to develop barley varieties with lower LOX by combination of low LOX-1 haplotype and other trans-regulation factors.