JIA-2018-09

1988 TAO Zhi-qiang et al. Journal of Integrative Agriculture 2018, 17(9): 1979–1990 results indicate that zinc fertilizer could significantly improve NR activity in flag leaves of the two cultivars that have been exposed to a high temperature stress. 4.2. Response of the content of flour protein compo- nents to zinc fertilizer and high temperature stress Gluten is the main component of flour proteins. Gluten proteins include gliadin and glutenin, and are the main storage proteins of wheat flour that directly affect the processing quality of flour (Goesaert et al . 2005). In contrast, the non-gluten proteins, albumin, and globulin, are mainly structural proteins with high nutritional value because they are rich in lysine and other important amino acids (Wieser and Seilmier 1998). Availability of nutrients, such as N, S, Cu, and Zn, affect flour protein components (Zhao et al . 2013). It is possible that the addition of zinc fertilizer significantly enhanced NR and GS activities and subsequently affected grain protein content and flour protein components (Liu et al . 2015). The content of albumin, glutenin, and gliadin increased and then decreased with the increase of zinc fertilizer (0–45 mg Zn kg –1 soil), where contents peaked in the 15 mg Zn kg –1 soil treatment. Zinc fertilizer addition also increased the ratio of glutenin to gliadin in GY2018. The ratio of glutenin to gliadin is correlated with wheat quality traits. The increase in glutenin content and thus, gluten content, can cause sedimentation and stabilization time to increase which results in improved flour processing characteristics (Zhao et al . 2013). The flour protein components that we examined may be affected by zinc and cysteine. Cysteine is a deoxidizer that alters the two sulfur bonds between and within protein molecules that promotes gluten formation. Cysteine-rich binding proteins with low relative molecular mass are able to bind to zinc with high affinity. Thus, Zn combined with cysteine rich binding proteins can affect flour protein composition (Zhang et al . 2012; Liu et al . 2015). Although this greenhouse experiment provided valuable evidence, field studies are required to fully understand the underlying mechanisms and consequences of zinc fertilizer on flour protein components. Exposure to the high temperature stress caused a reduction in grain yield and grain weight, and an increase in grain protein content (Wang et al . 2008). Results also showed that the amounts of grain protein components, albumin, gliadin, and glutenin, increased in plants of both cultivars that experienced the short-term HTS at D20. The likely reason is that the effect of HTS on starch synthesis in grain was greater than that on protein synthesis. A large decrease in starch can result in a decrease in grain weight and a relatively large increase in grain protein content 0 26 52 78 104 130 GY2018-2016 Gliadin content Glutenin content Albumin content Globulin content 0 26 52 78 104 130 Protein components content (mg kg –1 ) Protein components content (mg kg –1 ) Protein components content (mg kg –1 ) Protein components content (mg kg –1 ) ZM8-2016 A C 0 26 52 78 104 130 GY2018-2017 0 26 52 78 104 130 ZM8-2017 B D N-Zn0 N-Zn15 N-Zn30 N-Zn45 H-Zn0 H-Zn15 H-Zn30 H-Zn45 N-Zn0 N-Zn15 N-Zn30 N-Zn45 H-Zn0 H-Zn15 H-Zn30 H-Zn45 N-Zn0 N-Zn15 N-Zn30 N-Zn45 H-Zn0 H-Zn15 H-Zn30 H-Zn45 N-Zn0 N-Zn15 N-Zn30 N-Zn45 H-Zn0 H-Zn15 H-Zn30 H-Zn45 Fig. 7 Effect of zinc fertilizer additions (Zn0–45 mean 0, 15, 30, and 45 mg Zn kg –1 soil, respectively) and high temperature stress (H) or no-stress (N) on different grain protein components of each wheat cultivar, Gaoyou 2018 (GY2018) in 2016 (A) and 2017 (B) and Zhongmai 8 (ZM8) in 2016 (C) and 2017 (D).