Gibberellins & Abscisic Acid
Gibberellins named after fungus Giberella, causes rice plants to grow abnormally tall; discovered 1920’s; forms (GA1, GA2…)
Promote stem elongation, produced in apical parts of stem & roots
Dwarf mutants lack expression of gibberellin gene
Seed germination: embryo produces GA and sends it to endosperm cells; in endosperm cells, GA promotes expression of a-amylase, which converts stored starch to glucose ? embryo nutrition
Economic application: applied to grape flowers to extend internodes ? fruits have more room to ripe
Abscisic acid: antagonist to GA; inhibits seed germination (concentrations increase during late embryogenesis); forming winter buds, suppress length growth. Effects very rapid (few minutes) ? not by gene regulation?