Gibberellic acid bioassay

Samples were homogenized in ice-cold 80% (v/v) aqueous methanol and stirred for 12 h at 4°C. Samples were centrifuged at 14,000x g for 15 min. The pellets were separated from the supernatant and re-extracted twice. The combined supernatants were reduced to the aqueous phase and the pH adjusted to 3.0. The aqueous phase was then partitioned four times against water-saturated ethyl acetate (EtOAc). The EtOAc extracts were dried by evaporation and the samples were resuspended in water. Gibberellins were quantified by dwarf-rice bioassay (Oryza sativa L., cv. Tan-Ginbozu) as previously described by Jones and Varner [25].