Nitrogen (N) nutrition, post-anthesis temperature and drought-induced changes in the kinetics of accumulation of dry mass, total grain N and protein fractions (albumins-globulins, amphiphils, gliadins, and glutenins) contents were examined for winter wheat (Triticum aestivum L.). Crops were grown in controlled environment tunnels in 1994 and 1998. In 1994, five post-anthesis temperatures averaging from 15-25 degrees C were applied during grain-filling. In 1998 two post-anthesis temperatures averaging 13 degrees C and 20 degrees C were applied and factorized with two post-anthesis water regimes. In 1994 crops also were grown in the field, where different application rates and timing of N nutrition were tested. When expressed in thermal time, the kinetics of accumulation of the protein fractions were not significantly affected by post-anthesis temperature or drought; whereas N nutrition significantly increased the rate and duration of accumulation of storage proteins. Albumin-globulin proteins accumulated during the early stage of grain development. The rate of accumulation of that fraction decreased significantly at c. 250 degrees Cd after anthesis, when the storage proteins (gliadins and glutenins) started to accumulate significantly. Single allometric relationships for the different environmental conditions exist between the quantity of each protein fraction and the total quantity of N per grain. From these results it was concluded that (1) the process of N partitioning is neither significantly affected by post-anthesis temperature or drought nor by the rate and timing of N nutrition and (2) at maturity, variations in protein fraction composition are mainly because of differences in the total quantity of N accumulated during grain-filling.

A functional explanation for the regulation of grain nitrogen (N) accumulation in cereal by environmental and genetic factors remains elusive. Here, new mechanistic hypotheses of grain N accumulation are proposed and tested for wheat (Triticum aestivum). First, we tested experimentally the hypothesis that grain N accumulation is mostly source regulated. Four contrasting cultivars, in terms of their grain N concentrations and yield potentials, were grown with non-limiting N supply. Grain number per ear was reduced by removing the top part of the ear at anthesis. Reduction in grain number gave a significant increase in N content per grain for all cultivars, showing that grain N accumulation was source regulated. However, on a per ear basis, cultivars with a high grain number fully compensated their N accumulation for reduced grain number at anthesis. Cultivars with a lower grain number did not compensate completely, and grain N per ear was decreased by 16%. Second, new mechanistic hypotheses of the origins of grain N source regulation and its response to environment were tested by simulation. The hypotheses were: (a) The regulation by N sources of grain N accumulation applies only for the storage proteins (i.e. gliadin and glutenin fractions); (b) accumulation of structural and metabolic proteins (i.e. albumin-globulin and amphiphilic fractions) is sink-regulated; and (c) N partitioning between gliadins and glutenins is constant during grain development and unmodified by growing conditions. Comparison of experimental and simulation results of the accumulation of grain protein fractions under wide ranges of N fertilization, temperatures, and irrigation supported these hypotheses.One challenge for global nutrition in the next decade is to increase food yield per unit ground area in a sustainable manner while maintaining its end use value (Cassman, 1999; Tilman, 1999; Tilman et al., 2002). Grain protein concentration and composition are major determinants of grain nutritional value (Feil, 1997). The concentration of Lys in grain, the most limiting amino acid in cereals for human and monogastric animals, increases with increasing grain protein concentration (Feil, 1997) despite the decrease of its concentration in total protein (Mossé et al., 1985). Grain protein concentration and composition are also the major determinants of flour functional properties (Weegels et al., 1996;Shewry and Halford, 2002). However, the inverse relationship between grain yield and protein concentration, reported for several species, may prevent breeders from improving these two traits simultaneously (Stewart and Dwyer, 1990; Delzer et al., 1995; Feil, 1997; Brancourt-Hulmel et al., 2003). To break this inverse relationship, genetic increments in grain protein yield must keep pace with those in grain yield.Therefore, efforts to overcome the inverse relationship between grain yield and protein concentration must concentrate on improving grain protein accumulation per square meter and per grain (Feil, 1997; Triboï and Triboï-Blondel, 2002...

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High temperatures during grain filling have been reported to be one of the factors that can affect the dough properties and quality characteristics of wheat. Responses to high temperature have been related to changes in protein composition at both quantitative and qualitative levels. The present study was conducted to determine the influence of high temperature during grain filling on the protein composition of bread wheat evaluated by proteomic tools. Plants were grown in the field and transferred to cabinets soon after flowering. They were subjected to two thermal regimes 18 degrees C/10 degrees C (day/night) and 34 degrees C/10 degrees C. Total proteins were extracted from control grains and treated plants at three different post-anthesis stages. The proteins were separated by two-dimensional gel electrophoresis and analysed by Melanie 3 software. Of the total number of mature wheat grain proteins, 37 were identified as significantly changed by heat treatment. Analysis by matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectrometry coupled with database searching allowed the characterization of 25 heat-induced proteins and only one heat-decreased protein spot. To learn more about the function of the identified proteins, we examined their expression during treatment.

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