JXB Advance Access originally published online on February 27, 2004
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Journal of Experimental Botany, Vol. 55, No. 398, pp. 919-927, April 1, 2004
© 2004 Oxford University Press
Plants and the Environment |
Effects of a PAL inhibitor on phenolic accumulation and UV-B tolerance in Spirodela intermedia (Koch.)
Received 3 September 2003; Accepted 19 December 2003
1 Cropping Systems Research Laboratory, ARS-USDA, Lubbock, TX 79415, USA
2 Natural Resource Sciences and Landscape Architecture, University of Maryland, College Park, MD 20741, USA
3 Department of Botany; 392 Pearson Hall; Miami University, Oxford, OH 45056, USA
* To whom correspondence should be addressed. Fax: +1 513 529 4243. E-mail: huertaaj{at}muohio.edu
Duckweed (Spirodela intermedia) was grown axenically on 1/2 strength Hutners nutrient solution plus 1% sucrose, with the L-phenylalanine ammonia-lyase (PAL) inhibitor 2-aminoindan-2-phosphonic acid (AIP) at 0.0, 0.05, or 10 µM, at constant 25 °C and a light intensity of 300 µmol m2 s1 photosynthetically active radiation from CW fluorescent lamps. Growth with 10 µM AIP led to decreased frond area and fresh weight, but dry weight was unchanged. Microscopic examination of fronds revealed increased frond thickness and a lack of reticulate aerenchyma. Ultraviolet epifluorescence microscopy and UV-Vis spectroscopy of methanolic extracts confirmed the dose-dependent inhibition of secondary phenolic synthesis with the near total elimination of secondary phenolic accumulation at the 10 µM level. AIP-treated plants showed increased sensitivity to UV-B as shown by a reduced Fv/Fm. The results provided direct evidence of the working hypothesis that phenols function to screen UV radiation from reaching photosynthetic tissues or damaging other sensitive tissues. A novel histochemical method employing zirconyl chloride to visualize phenols is discussed.
Key words: AIP, aminophosphonic acid, duckweed, flavonoid, PAL, phenolic, Spirodela, ultraviolet-B, UV.