N Partitioning between Gluten Fractions in a Set of Italian Durum Wheat Cultivars: Role of the Grain N Content

Abstract

Grain protein content constitutes a key quality trait for durum wheat end-products and may also impact grain protein composition. A total of sixteen durum wheat cultivars were analyzed in a field trial during two seasons at two nitrogen (N) levels to evaluate whether and to what extent the variation in total grain N was associated with variation in the quantity of the various protein fractions and grain quality parameters. Genotypic variation in grain N content correlated with the variation in the content of all three protein fractions, although the strength of the correlation with gliadin and albumin-globulin was higher than that with glutenins. Genotypic variation in gliadin and glutenin content was more tightly correlated with the variation in the sulfur (S)-rich protein groups than with the S-poor protein groups and subunits. The variation in the percentage of unextractable polymeric proteins (UPP%) among genotypes was independent of their glutenin allelic composition. The significant genotypic differences in UPP% and in the ratios between protein groups and subunits were not influenced by the corresponding variation in grain N content. The final grain N content can only account for part of the variation in quality parameters and in the partitioning of total grain N between protein fractions since genotypic differences other than grain N content also contribute to these variations.

Keywords: S-rich/S-poor; durum wheat; gliadin/glutenin; grain N content; grain N partitioning.

Figure 1

Rainfall (blue bars), reference evapotranspiration (ETo) (orange bars), and rainfall deficit (rainfall–ETo) (grey bars) between October and May for the years 2016 and 2017, plus the long-term mean (40 years; 1970–2010).

Figure 2

Relationships between the variation in the total grain nitrogen and the N content of the three protein fractions: glutenins (GLU) (squares), gliadins (GLI) (circles), and albumins-globulins (ALBGLOB) (triangles). Points are cultivar means across years and N treatments. *** p ≤ 0.001.

Figure 3

Relationships between the variation in the µg of total gliadins per grain and the content of the three gliadin components: alpha/beta (squares), gamma (triangles), and omega (circles). Points are cultivars means across years and N treatments. ***, p ≤ 0.001; ns, not significant.

Figure 4

Relationships between the variation in the µg of total glutenins per grain and the amount of the two glutenin components: LMW-GS (triangles) and HMW-GS (circles). Points are cultivar means across years and N treatments. *** p < 0.001, ** p < 0.01.