Journal
JOURNAL OF PLANT GROWTH REGULATION
Volume 21, Issue 4, Pages 459-468Publisher
SPRINGER
DOI: 10.1007/s00344-002-0022-3
Keywords
Petunia x hybrida; ethephon; indole-3-acetic acid; isopentenyladenosine; zeatin riboside; lateral shoots; plant architecture
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Seedlings of Petunia x hybrida 'Orchid' treated with the ethylene-releasing compound ethephon at 0.9, 1.7, an 3.5 mM evolved ethylene at a higher rate as the concentration of ethephon increased. Regardless of the concentration of ethephon applied, ethylene evolution peaked 6 to 8 h following application. Evidence that ethephon application decreased apical dominance included an increase in the number of new nodes on the main stem and a sustained increase in the length of new and existing lateral shoots compared to the control (no ethephon). Plants treated with 3.5 mM ethephon developed mild chlorosis, whereas a concentration of 1.7 mM ethephon decreased apical dominance without phytotoxic effects. The auxin/cytokinin ratio decreased in the apical shoot section as early as I It after ethephon treatment. In contrast, a decrease in the ratio in the subapical shoot section was not detected until 24 h after ethephon application. Reduction in auxin/cytokinin ratio was a result of a decrease in indole-3-acetic acid (IAA) and an increase of zeatin riboside (ZR), but not isopentenyladenosine (iPA). These results suggest that exposing 'Orchid' petunia seedlings to ethylene via ethephon lowers the auxin/cytokinin ratio, thereby promoting the outgrowth of lateral shoots.
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