Submitted to: Journal of Experimental Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/19/2003
Publication Date: 2/27/2004
Citation: Gitz, D.C., Liu-Gitz, L., Mcclure, J.W., Huerta, A. 2004. Effects of a pal inhibitor on phenolic accumulation and uv-b tolerance in spirodela intermedia (koch). Journal of Experimental Botany.55(398)919-927. Interpretive Summary: Scientists have been interested in how plants cope with stress from the ultraviolet (UV) radiation for decades. Until recently the only method of directly testing ideas about how plants cope with UV stress was by making mutants, a time consuming and expensive task. This work provides direct evidence of UV screening by phenols without resorting to manipulating genes. Phenols are compounds produced by plants, which are thought to act as sunscreens and antioxidants in plants. This report also describes a new method for visualizing phenols in plant tissues. Because this manuscript provides additional tools for researchers to use, it is important to plant physiologists, biochemists, and breeders seeking to understand the prevention of UV induced stresses, as well as other plant stresses. The consumer will benefit from such understanding, because crops which resist UV and related stresses will have higher yields, which translates into lower prices in the store.
Technical Abstract: Duckweed (Spirodela intermedia) was grown axenically on 1/2 strength Hutner's 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 :M, at constant 25° C and 300 µE m-2 s-1 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 dose dependent inhibition of secondary phenolic synthesis with near total elimination of secondary phenolic accumulation at the 10 :M 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 before reaching photosynthetic tissues or damaging other sensitive tissues. A novel histochemical method employing zirconyl chloride to visualize phenols is discussed.