Influence of abscisic acid on flowering in Phalaenopsis hybrida

Abscisic acid (ABA) in the buds (or flowering shoots), leaves and roots of Phalaenopsis hybrida (cv. TS 340) was identified and quantified by gas chromatography-mass spectrometry-selected ion monitoring using hexadeuterated ABA as an internal standard. Leaves contained much lower levels of both free and bound ABA than did roots. Dormant buds contained a relatively higher level of free ABA, whereas no detectable free or bound ABA was found in flowering shoots either at a length of 2–3 cm or 7–10 cm. In dormant-stage P. hybrida (grown at 28 °C), levels of free ABA in the roots were higher than those in plants with flowering shoots; the levels of bound ABA in roots exhibited the opposite tendency. Free and bound ABA in leaves was slightly increased in plants with flowering shoots as compared to those in the dormant stage. In addition, exogenous ABA application at 0.1 or 1 μg per plant inhibited initiation of flowering shoots, especially at 1 μg per plant. These results suggest the decrease in the free ABA contents in the roots and buds, but not in the leaves, is correlated with bud activation and the development of flowering shoots.