To study the role of abscisic acid (ABA) and gibberellin (GA) sensitivity in regulating pre-maturity
a-amylase (PMA) in wheat grains, plants were grown in a glasshouse under cold-shock and ambient
conditions. a-amylase activity in response to applied ABA and GA was measured in detached-grains with
the embryo removed (in vitro) and in intact-grains attached to the plant (in situ). The in vitro experiment
was conducted using Spark (low PMA-susceptible genotype) and Rialto (highly PMA-susceptible
genotype), with the aim of defining the time point for GA-sensitivity. The results showed an increase
in GA-sensitivity at about 640 degree days after anthesis (DAA) in Rialto. There was no evidence for a
change in ABA-sensitivity in either variety. The in situ experiments were conducted using genotypes from
a Spark Rialto doubled haploid population segregating for the Rht-D1a (tall) or Rht-D1b allele and for
the presence or absence of 1BS/1RS. For Rht-D1a (tall) or Rht-D1b genotypes with or without 1BS/1RS, the
cold-shock significantly increased GA-sensitivity, whereas there was no significant change in
ABA-sensitivity. These results show PMA is related to an increase in GA-sensitivity that occurs in the
aleurone at around 640 degree DAA, and can be enhanced by environmental factors (e.g. cold-shock).
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