Environmental effects on the quality of two wheat genotypes: 1. quantitative and qualitative variation of storage proteins

Abstract

A new method of sequential extraction of proteins followed by quantitative and qualitative determination by reverse-phased high-performance liquid chromatography (RP-HPLC) was used to analyse the effect of environmental conditions (3N fertilisation rates, two varieties, two sites and two growing seasons) on quantitative and qualitative variation of wheat storage proteins. The results showed that N supply (fertilisation and site) was the most important environmental factor affecting protein content and composition. The most important effect was quantitative: the total protein, protein unit and subunit contents increased with the supply of nitrogen to the grain. As grain protein increased, the gliadin and glutenin contents and the gliadin to glutenin ratio increased. Gliadin showed a higher correlation with total protein content than glutenin. In the variety Rinconada, glutenin content was higher than that in Bancal. As total glutenin increased, both high and low-molecular weight (HMW and LMW) fractions increased and their ratio (HMW/LMW) did not change significantly, despite a slope of LMW subunits two times greater (0.69) than that of HMW fractions (0.31). The quantity of each HMW subunit (RP-HPLC peak) increased with total HMW-glutenin, but their relative percentage increased for some peaks and decreased for others. The composition of the HMW subunit was more stable in Bancal than in Rinconada. This general pattern of variation was also characteristic of the LMW subunit. Concerning gliadin composition we noted that the content of different gliadin monomers (RP-HPLC peaks) or pools of monomers (α-, β-, γ-, ω-gliadin) increased with total gliadin content. The proportion of certain peaks was stable whereas the contribution of other peaks was related to the variation in gliadin content and depended on the variety.