Effect of heat shock during grain filling on the gluten protein composition of bread wheat

The present study was conducted to determine the role of the variation of the temperature during grain filling on the protein composition of bread wheat evaluated by SE-HPLC. Four cultivars were grown in four typical areas of wheat cultivation in Italy; at each location, four different temperature profiles were imposed during grain filling by anticipating or delaying sowing date in the South of Italy (Foggia and Catania) or by covering the plots with plastic tunnels in the North (Milano) and in Central Italy (Viterbo). Results indicated that, independently of the genotype, growth environment (location) and different temperature regimes affect quality characteristics by allowing the synthesis of a different amount of total proteins or providing a different pattern of protein fraction accumulation. In the latter case, more pronounced effects were observed during frequent episodes of daily maximum temperatures above 35 degrees C, particularly in the plots covered with plastic tunnels during grain filling at Milano and Viterbo. At both locations, high temperatures seemed to mainly affect the composition of the polymeric fraction: particularly the formation of larger aggregates, without influencing their total amount. The relative quantity of insoluble polymeric proteins for heat stressed samples was, in fact, significantly lower than those for samples from the normal (control) and late sowings, whereas this situation was completely reversed when the relative amount of the easily soluble polymeric proteins was considered. The possible influence of temperature on the mechanism by which intermolecular disulphide bonds are formed and the effect on composition of polymeric fractions during the deposition of storage proteins are discussed. (C) 1996 Academic Press Limited