Changes in levels of endogenous hormones in azalea released from apical dominance

Enzyme-linked immunosorbent assays were used to quantify the levels of endogenous hormones in the 0.5 cm of shoot below the terminal bud (the shoot segment, where the lateral bud will emerge) of 'Siji' azalea (Rhododendron obtusum) when intact plants had been sprayed with 5% (w/v) Off-Shoot-O, a chemical pinching agent, or decapitated. The contents of indole-3-acetic acid, isopentenyladenine and isopentenyladenosine, zeatin and zeatin riboside, dihydrozeatin and dihydrozeatin riboside, gibberellins and abscisic acid were assayed. It was found that decapitation and Off-Shoot-O treatment could increase the concentrations of endogenous cytokinins and decrease the concentrations of indole-3-acetic acid in the shoot segment. On the other hand, both the Off-Shoot-O treatment and decapitation could elicit an increase in gibberellins concentrations and a decrease in abscisic acid concentration, suggesting that gibberellins and abscisic acid may be also involved in the growth of lateral buds.