1. Introduction
Wheat protein content and baking quality, highly depend on genotypic and environmental
factors and it is recognised that variation in protein content and composition significantly
modify wheat quality. Rousset et al., 1985; Bietz, 1988; Borghi et al., 1995.
Many studies have been conducted in an at- tempt to explain wheat quality variation as a
function of genetic variation in protein composi- tion. The major storage proteins in wheat are the
gliadins and glutenins. Gliadins are subdivided into a, b, g and v units and glutenins into low
and
high molecular
weight LMW-GS
and HMW-GS. The genetic control and the relation-
ships between gluten protein composition and quality characteristics are better and better under-
stood Shewry et al., 1989; Colot, 1990; Halford et al., 1992; Gupta and MacRitchie, 1994;
Popineau et al., 1994; Weegels et al., 1996; Fido et al., 1997; Martinant et al., 1998; Metakovsky and
Branlard, 1998.
With regard to environmental effects several previous studies reported, at different levels of
investigation, some
variations in
protein composition:
the amino-acids composition g aa100 g proteins varies with the N content of the grain
Mosse et al., 1985; Triboi et al., 1990; Bulman et al., 1994; Boila et al., 1995;
the quantity of N and S in the grain increases with N content, but the NS ratio decreases:
this reflects a change in the ratio between protein with lower sulphur content such as
certain gliadins and higher sulphur proteins such as glutenins Byers and Bolton, 1979;
Triboi et al., 1990; MacRitchie and Gupta, 1993;
the gliadinglutenin ratio increases with the quantity of N in the grain Terce-Laforque and
Pernollet, 1982; Triboi et al., 1990; Triboi and Leblevenec, 1995;
the concentration of some gliadin bands, mea- sured by electrophoresis and densitometry,
changes with the variation in N supply to the grain Brandlard and Triboı¨, 1983.
Progress in analytical technology and particu- larly in RP- and SE-HPLC has enabled a better
understanding of the effects of protein composi- tion Marchylo et al., 1989; Lookhart, 1997. As
electrophoresis, HPLC not only separates differ- ent gliadin and glutenin subunits but also
quantifies individual or pooled subunits. How- ever, this technique has been used in few studies
and quantitative determination of protein units and subunits and their relationships with quality
have seldom been described Marchylo et al., 1989; Seilmeier et al., 1990; Sutton et al., 1990;
Kolster et al., 1991; Sutton, 1991; Wiesser et al., 1994. Subsequently, the quantitative changes can
be accompanied by qualitative changes reflected in the ratios between different components Triboi
and Triboı¨-Blondel, 1998; Daniel et al., 1998a,b. Changes in the ratios between different protein
units and subunits have rarely been signalled, and the effects on the technological properties have
often not been established.
Generally, two aspects can be considered in the research on environmental effects:
1. the change in grain composition and particu- larly in the quantity and quality of proteins;
2. the relationship between protein changes and quality parameters.
This paper deals with the first aspect: the effect of environmental conditions N fertilisation rate,
site and growing season on the quantitative and qualitative variation of wheat glutenin and gliadin
units and subunits. A new method of sequential extraction of proteins followed by quantitative
determination by RP-HPLC was performed in order to analyse the qualitative changes induced
by quantitative variations and to establish the relationships between different protein units and
subunits for modelling purposes.
2. Materials and methods
Kategori