Lipoxygenase(LOX) And The Discoloration Of Foxtail Millet During Storage

Foxtail millet (Setaria italica (L.) Beauv.) is an important crop in northern China. The dehulled millets, the primary processing products of foxtail millet, are very popular among consumers for its high nutritional values. Millet colour is an important index to evaluate foxtail millet quality. However, the discoloration of millet during the storage reduces the value of the millet and also the quality sTab.ility of millet products, which has been restricting the development of millet industry. In this study, four famous millet varieties, Jingu21, Qinhuang2, Yugul, Longgu25 were selected as research materials. At different storage stages, the millet color and total caronenoids of different varieties were measured, and the LOX activities were analysed. The full length of fourteen LOX genes were cloned and analyzed with relavent bioinformatics. Meanwhile, the millet colour of 360 varieties of foxtail millet was measured during storage to determine the change chatacter of their millet color. The varieties with significantly different discoloration rates were selected as research materials. The expression patterns of all gene family members of LOX were compared among different millet varieties during grain maturing stages. This study explored the mechanism of millet discoloration from both the physiological and molecular levels, which would lay a foundation for developing molecular markers and improving the molecular breeding efficiency of foxtail millet. The main results are as the followings:1. The millet color of four varieties measured using X-Rite VS450 colorimeter periodically and characterized by b* value was correlated with their total carotenoid contents measured by UV spectrophotometry. The results showed that genotype had significant impact on millet color and total carotenoid contents. Different characters of millet discoloration showed among different varieties. The b* value and the total carotenoid contents showed positive correlation.2. The LOX activities of four varierties were analyzed using UV spectrophotometry during different storage. The results showed that the LOX activities in Longgu25, Qinhuang2 and Yugul shared the similar trend, increasing at first period and then decreasing. Whereas the LOX activity of Longgu25 reached a maximum of 63.84 AU/g min in May, it had only a slight increase at the same time in Jingu21.3. Fourteen LOX genes were analyzed using bioinformatics including homology analysis, prediction of chloroplast transit peptide and phylogenetic tree construction. Meanwhile, genomic sequences of LOX genes of varieties were cloned and compared with each other. Combining these result with the expression profile of 14 LOXgenes in different tissues (root, stem, leaf, spike) in Jingu21, three LOXgenes, Si038999, S1000274 and Si003946, were considered to be probably associated with millet colour.4. b* value was used to analyze millet color index of 360 foxtail millet resources. Varieties with the fastest and slowest (three each) discoloration characteristic were selected among 360 resources.5. Si038999, Si000274 and Si003946 were further cloned and analyzed in these selected varieties. Sequence alignments results showed that the protein sturcture of three LOX genes had significant difference between varieties. The expression pattern of these three genes at different maturation stages showed that the relative expression of Si038999 and Si003946 in B280 and B187, which had a slow discoloration characteristic, were higher than the varieties with fast discoloration rate.Above all, the speed of millet discoloration was related with high lipoxygenase activity and the different protein sturcture during storage. Thus, lipoxygenase might be one of the important factors causing millet discoloration.