The regulatory role of the auxin in the creeping chrysanthemum habit

The chrysanthemum (Dendranthema morifolium) variety ‘Yuhuajinhua’ has a creeping growth habit. An ELISA-based assessment of the content and distribution of IAA in the stem of ‘Yuhuajinhua’ showed that there was an IAA concentration gradient across the stem segment between the 2nd and 4th nodes, counting from the apex, before the creeping growth, while this difference disappeared after the initiation of creeping growth. An immunohistochemical assay for IAA showed that auxin was concentrated in the epidermis and cortex of the proximal side of the stem, particularly in the first few hours after gravitational stimulation was applied. The bending of the stem was generated by the asymmetric elongation of the epidermal cells in proximal side of the stem, especially upon to 6 h after gravistimulation, and this was probably mediated by an alteration in the IAA gradient across the stem. Exogenously applied 1-naphthaleneacetic acid (NAA) or 2,3,5-triiodobenzoic acid (TIBA) played converse effects on the gravitropic stem curvature. The data support the idea that IAA plays a crucial regulatory role in the formation of the creeping habit in the chrysanthemum variety ‘Yuhuajinhua’.