The effect of temperature shock and grain morphology on alpha-amylase in developing wheat grain

Background and Aims The premature production of alpha-amylase without visible germination has been observed in developing grain of many cereals. The phenomenon is associated with cool temperatures in the late stages of grain growth but the mechanisms behind it are largely unknown. The aim of this study was to replicate the phenomenon under controlled conditions and investigate the possibility of a mechanistic link with grain size or endosperm cavity size. Methods Five wheat (Triticum aestivum) genotypes differing in their susceptibility to premature alpha-amylase were subjected to a range of temperature shocks in controlled environments. A comparison was then made with plants grown under ambient conditions but with grain size altered by using degraining to increase the assimilate supply. At maturity, alpha-amylase, grain area and endosperm cavity area were measured in individual grains. Key Results Both cold and heat shocks were successful in inducing premature alpha-amylase in susceptible genotypes, with cold shocks the most effective. Cold shocks also increased grain area. Degraining resulted in increased grain area overall, but the larger grain did not have higher alpha-amylase. Analysis of individual grain found that instances of high alpha-amylase were not associated with differences in grain area or endosperm cavity area. Conclusions Pre-maturity alpha-amylase is associated with temperature shocks during grain filling. In some cases this coincides with an increase in grain area, but there is no evidence of a mechanistic link between high alpha-amylase and grain or endosperm cavity area.