Nitrogen-Sulphur Fertiliser Induced Changes in Storage Protein Composition in Durum Wheat

Abstract

A set of Argentinean and Chilean cultivars of durum wheat were subjected to the following fertiliser regimes in designed field trials grown over three years: NOSO (no applied nitrogen or sulphur fertiliser), N1S0 (applied nitrogen fertiliser only), NISI (both applied nitrogen and sulphur fertiliser) and NOS I (applied sulphur fertiliser only), where N was applied as urea and S as potassium sulphate. Two protein extraction protocols were applied to each flour sample obtained from the trial, one for reduced glutenin subunits and one for the gliadins. The resultant extracts were separated by SDS-PAGE, the gels were scanned and the images analysed densitometrically. The data obtained were analysed statistically in order to determine whether the following quantities varied over cultivars and over fertiliser treatments: (i) the relative proportion of total gliadins to total glutenins (Gli:Glu ratio); (ii) the relative proportion of individual omega-gliadin proteins to other gliadin proteins; and (iii) the relative proportion of HMW to LMW subunits of glutenin (HMW:LMW ratio). Such variation would be expected in the light of previous studies in wheat and given that sequence data have shown that these components vary in molecular S-content. It was found that (a) one of the cultivars (cv. Bonerense INTA Cumenay) showed relatively high Gli:Glu ratios compared to the other cultivars; (b) the fertiliser treatment NOSO gave higher Gli:Glu ratios than the remaining treatments in the two years where significant differences were observed; (c) two of the cultivars (cv. B. I. Cumenay and cv. Chagual INIA) generally gave higher HMW:LMW ratios than the remaining two (cv. Bonaerense INTA Facon and cv. Buck Topacio); (d) the treatments involving N-application (N1S0 and NISI). generally showed higher HMW:LMW ratios than those without N-application (NOSO and NOS I); (e) although effects of S-appiication were observed, these were inconsistent over years; (f) Cv, B. I. Cumenay showed relative stability over fertiliser treatments for the quantities evaluated, coherent with its previously observed stability for industrial quality characteristics. The findings hopefully contribute to our understanding of why cultivars differentially respond to fertiliser treatments for quality characteristics.