Department of Biological Sciences, Texas Tech University, Lubbock, Texas, 79409
1 This work was supported by National Science Foundation Grant No. GB-7510 and State Supported Research TTU-191-4771.
The effects of the phytochrome reaction and those of the endogenous rhythm in the photoperiodic lowering response were analyzed by assaying endogenous gibberellins and gibberellin precursors found in Pharbitis nil strain Kidachi, following photoperiodic treatments designed to separate those two components. Compounds similar to gibberellins were detected with thin-layer and gas-liquid chromatography, but only the presence of gibberellin precursors could be confirmed with mass spectrometry. Kaurene and kaurenoic acid, both precursors in the biosynthesis of gibberellin, were detected in plants grown under vegetative conditions, while only kaurene was found in plants induced to flower. Qualitative and quantitive differences in the GA precursors of plants subjected to diurnal or bidiurnal photoperiodic treatments indicate that the effects of phytochrome and those of endogenous rhythms influence floral induction in different ways.
