Studies On Cultivar And Environmental Variation Of Arabinoxylan Content And Endo-Xylanase Genes In Bailey

Quality of malting barley is affected by many factors and a non-starch polysaccharide-arabinoxylan (AX) is one of the key factors. When degradation of AX is not sufficient during malting, it will hinder the release of nutrients in the endosperm, and the remaining AX may enter the wort, resulting in increased viscosity, hindering subsequent filtering and processing. Finally, it deteriorates the taste of beer and quality. In this paper, barley cultivars with different quality traits were used to study the effect of genotype and environment on arabinoxylans (AX) contents and endoxylanase activity (EA) in grains and malts. During grain filling stage, the dynamics of EA and AX content were investigated; and the influence of some agronomic factors and temperature during grain filling on grain AX content and EA were also studied. In addition, the sequence, structure, and expression of the gene encoding endoxylanase, which hydrolysises the AX were analyzed. The main results were as follows:1. Clutivar and environmental variation of arabinoxylan content in barleyEight two-rowed barley cultivars with the similar growing period and different malting quality were used, and planted in seven locations with different ecological conditions, to study the cultivar and environmental impact on AX and EA. Average TAX content was4.1%for eight cultivars planted on all locations, and the coefficient of variation (CV) among cultivars across over locations differed greatly, ranging from4.1%(Yancheng) to23.4%(Zhumadian), while the CV for cultivars ranged from11.7%(Zhepi33) to23.4%(Supi4). Overall, average CV for cultivars (18.1%) was much higher than that for locations (9.5%), indicating that the effect of cultivar on AX content was greater than that of environment. Average endoxylanase activity (EA) of all cultivars over all locations was2.62U g’1, and the EA value ranged from2.33(Shanghai) to2.88U g-1(Yancheng) among locations, and from2.54(Supi6) to2.72U g-1(Hua30) among cultivars. The CV of EA among locations was from5.7(Shanghai) to11.1%(Wuhan), and among cultivars was from7.4(Zhepi33) to14.3% (Hua30). The average CVs among cultivars (10.4%) and among locations (8.4%) was just same, indicating the influence of environment and cultivar was quite close.2. Differences of arabinoxylan content and endoxylanase activity in grains and maltsThe AX content and EA were compared between malts and grains in67barley cultivars. Grain TAX content ranged from3.97to6.36%, and the mean was4.96%. Malt TAX content ranged from3.02to5.19%, and the mean was3.92%. Grain EA ranged from1.68to4.41U g-1, with an average of2.62U g-1, while malt EA ranged from8.26to19.23U g-1, with an average of12.25U g-1. The enzymatic hydrolysis rate of TAX was up to37%, with an average of around21%. The low hydrolysis rate may be related with barley cultivars used in this experiment, or the enzyme which had isozymes or its specificity was not high.3. Grain AX content changes over different cultivation conditionsThree barleys with different malting quality were used to study dynamics of TAX content and EA during grain filling. The results showed that both AX and EA had a downward trend during grain fillage stage, and there was distinct difference among cultivars. The effect of some agronomic factors on AX and EA in barley Zheda9showed the influence varied with each factor. In general, under the conditions of medium seeding density, low nitrogen fertilizer and equal applyication of nitrogen fertilizer at seedlings and heading stages, grain TAX content was relatively lower. Grain TAX in Hangzhou was significantly higher than that in Tongxiang, probably due to the difference in soil fertility and temperature during grain filling. In addition, under in vitro culture, the influence of temperature on barley AX content was studied. The results showed that higher temperature increased grain AX content.4. NIRs model for analyzing barley arabinoxylan contentNear infrared spectroscopy model for analyzing barley grain AX content based on modified partial least squares (MPLS) regression calibration was established. With different spectral scattering process and mathematical treatment, the optimal model was obtained, and the cross-validation coefficient of determination was0.728. The model can be used in identification and screening of large-scale germplasm evauation and early generation breeding program.5. HvXYN1gene polymorphismThe gene HvXYN1encoding endoxylanase was sequenced, and its structure was analyzed in67barleys. The results showed that the intron and exon regions of the gene had different degrees of single base mutation and multi-abundant polymorphic loci. The HvXYNl genes in wild barleys and local cultivars were compared by Tajima’s neutrality test, and it showed the Tajima’s D values of wild barleys and cultivars was not significant, which supports neutral evolution model, indicating that the genes were not affected by the selection during domestication process. According to HvXYN1gene’s polymorphism in67barleys, the phylogenetic tree was constructed. The gene from different genotypes could be divided into two groups. Each SNP was analyzed with endoxylanase activity and TAX, and there was no correlation between each SNP locus and enzyme activity. However, it was detected that three loci were significantly associated with TAX content.6. Expression analysis of HvXYN1geneTwo barley cultivars differing in AX content and EA were used to study the expression of HvXYN1gene during grain filling. The results indicated that the expression of the gene had an upward trend at late grain filling, and there was an obvious difference between the two cultivars. Moreover, the expression of the gene had an inherent relationship with TAX content and endoxylanase activity, indicating the significance of further study on this issue.