Fluctuation in levels of endogenous hormones after decapitation and 6-benzyl amino purine treatment in azalea, and their relationship to apical dominance

Endogenous levels of indole-3-acetic acid (IAA), cytokinins, gibberellins (GAs) and abscisic acid (ABA) in 'Siji' azalea (Rhododendron obtusum), which had been sprayed once with 1000 mg/l B-benzyl amino purine (6-BA) or decapitated, were determined by enzyme-linked immunosorbent assays. It was found that decapitation could significantly decrease the level of IAA in the shoot segment (0.5 cm in length just below the terminal bud, where axillary buds will emerge). A single application of 6-BA elicited a decrease of IAA level in the shoot segment, whereas an increase of IAA level in the terminal bud, and elicited an increase of isopentenyladenine and isopentenyladenosine, zeatin and zeatin riboside, in both the shoot segment and the terminal bud. It was also found that both the 6-BA treatment and decapitation could elicit an increase of GA(1+3) level and a decrease of ABA level in the shoot segment (and the terminal bud). (C) 1997 Elsevier Science B.V.