Changes in protein composition during grain development in wheat

Changes in glutenin, gliadin, glutenin subunit composition, and polymer size distribution were monitored for 4 cultivars of wheat (Triticum aestivum L.) throughout grain filling in an irrigated and non-irrigated environment over 2 seasons. The synthesis of glutenin and gliadin was modelled using a logistic function to determine the rate and duration of synthesis in response to environmental conditions. The maximum rate of synthesis of glutenin occurred approximately 6–8 days after the maximum rate of gliadins, with the duration extended by a similar period. High molecular weight glutenin subunits (HMWGS) were detected earlier than low molecular weight glutenin subunits (LMWGS). After the initial synthesis of HMWGS, there was a period at approximately mid grain filling when the rate of synthesis was reduced, followed by a period of more rapid synthesis in the latter stages of grain filling. In contrast, once detected, LMWGS increased at a faster rate than, and were in excess with respect to, HMWGS. Cultivar and environmental differences were observed, but in all cases the average molecular weight of polymeric glutenin increased throughout grain filling. Large polymers (>400 kD) increased continuously during grain filling, whereas polymers in the range 150–400 kD remained relatively constant and smaller polymers <150 kD decreased. As grain filling approached physiological maturity, there was a rapid increase in the synthesis of large polymers. The gliadin to glutenin ratio was almost the same in grain from adjacent irrigated and non-irrigated environments subjected to high temperatures at mid grain f illing, but the proportion of highly polymeric glutenin was greater from the non-irrigated environment.