Late-maturity α-amylase expression in wheat is influenced by genotype, temperature and stage of grain development

Late-maturity alpha-amylase (LMA) is a genetic trait in wheat (Triticum aestivum L.) involving the production of alpha-amylase during grain development, which can result in an unacceptably low Falling Number (FN) in mature grain and consequent grain downgrading. Comparison of the FN test, an alpha-amylase activity assay and a high pI alpha-amylase-specific ELISA on the same meal samples gave equivalent results; ELISA was used for further experiments because of its isoform specificity. A cool temperature shock during the middle stages of grain development is known to induce LMA and is used for phenotypic screening. It was determined that a cool temperature treatment of seven days was required to reliably induce LMA. Glasshouse studies performed in summer and winter demonstrated that temperature affected the timing of sensitivity to cool-shock by altering the rate and duration of grain development, but that the sensitive grain developmental stage was unchanged at 35-45% moisture content. Wheat varieties with Rht-B1b or Rht-D1b dwarfing genes responded to a cool-shock only from mid grain filling until physiological maturity, whilst genotypes with Rht8c or without a dwarfing gene expressed LMA in response to a cool-shock during a wider developmental range. A continuous cool maximum temperature regimen (23 degrees C/15 degrees C day/night) during grain development also resulted in LMA expression and showed a stronger association with field expression than the cool-shock treatment. These results clarify how genotype, temperature and grain developmental stage determine LMA expression, and allow for the improvement of LMA phenotypic screening methods.