Chin-Hui, Shen , Krishnamurthy, Ramanarayan , Yeh, Kai-Wun .
Pectin degradation processes regulate IAA levels in Oncidium to initiate plant phase transition.
Oligogalacturonides are well known to modulate plant growth and development as an antagonist to auxin in bringing about various physiological changes in plants. Oncidium pseudobulb at different stages was differentiated as PB0 and PB3 depending on the length of the flowering bulb relative to the vegetative bulb. In this current research we have observed a decrease in the pectin content of the Oncidium pseudobulb which is accompanied by the decrease in the concentration of IAA. The observed reduction in pectin content is due to different mRNA expression level and activities of pectin methylesterase (PME) and polygalacturonase (PG) in PB0 and PB3 stages. In PB0, the mRNA expression level and enzymatic activity of PME were higher than PB3 compared to PG which exhibited a high expression level and low enzymatic activity in PB0 than PB3. Interestingly, the highest amount of ROS and H2O2 were detected in PB0 compared to both PB3 and later stage pseudobulbs which showed lower amounts. The high amount H2O2 may be arising from the over-demethylation of pectin due to the dynamic activity of PME. This results in the induction of oxidative burst thus initiating the oxidation of IAA before the influence of OGAs. The reduction in IAA may result in the transition of Oncidium during the phase transition. Apart from these, we also noticed that the activity of galacturonic acid reductase exhibited high activity in PB0 only, but galacturonic acid oxidase activity is higher at PB0 and PB3, especially in PB0 bottom portion that is near the flowering bulb. It is already known that active galacturonic acid oxidase produce more galactarate which has been reported to induce pexoxidase which would initiate the oxidation IAA. Therefore, these results would suggest a link between degradation processes of pectin and concentration of IAA which would influence plant phase transition.
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1 - Institute of Plant Biology, National Taiwan University
2 - Institute of Plant Biology, National Taiwan University
Presentation Type: Poster:Posters for Sections
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM