In contrast to standard-height wheat genotypes, short-statured wheats having major genes for dwarfness do not show increased seedling growth
after treatment with
gibberellic acid. Endogenous
gibberellic acid induces synthesis of
amylase in the endosperm of germinating seeds, but the amount of
amylase synthesized is greatly increased by exogenous
gibberellic acid treatment in standard-height and in short-statured wheats that have dwarfing genes from the variety "Norin 10." "D6899," which has the "Tom Thumb" gene for height reduction, had about one-fourth of the
amylase activity of standard-height and Norin 10-derived, short-statured wheats. This genotype showed little or no increased
amylase activity after
gibberellic acid treatment. Genetic analyses showed that the amount of
amylase synthesized was controlled by a single gene and was dependent on the number of copies of the structural gene present in the endosperm.
Dwarfism in wheat may be related to a blockage in
gibberellic acid utilization because other workers have found that the amount of endogenous
amylase synthesized in Norin 10-derived, short-statured wheats is not growth-limiting, but it is not known if low
amylase synthesis is related to
dwarfism in the Tom Thumb derivative. No recombinants were recovered in a small population, suggesting that the Tom Thumb gene may pleiotropically affect plant height and the lack of response to
gibberellic acid in
amylase synthesis and seedling growth.