Author
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Krizek, Donald |
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Submitted to: Photochemistry and Photobiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/3/2004 Publication Date: 4/15/2004 Citation: Krizek, D.T. Influence of PAR and UV-A in determining plant sensitivity and photomorphogenic responses to UV-B radiation. Photochemistry and Photobiology. 79(4):307-315. Interpretive Summary: The importance of ultraviolet radiation (UV)in plant development has been increasingly recognized. In recent years, it has become clear that plants have several compounds that serve as photoreceptors or signals, enabling the plant to respond to different wavelengths of radiant energy. The action of UV radiation works in concert with other wavelengths in the visible (400-700 nm) and UV-A (320-400 nm) region to provide protection against damaging UV-B (280-320 nm)wavelengths, provided that the ratios of these wavelengths are in proper balance. Although considerable progress has been made, further studies are needed to determine the interactions of UV-A, UV-B, and visible radiation under controlled-environment conditions. Efforts should be made to control, monitor, and characterize each of these wavebands when conducting UV enhancement studies. Technical Abstract: The role of photosynthetically active radiation (PAR) in modifying plant sensitivity and photomorphogenic responses to UV-B radiation has been examined by a number of investigators but few studies have been conducted on UV-A, UV-B and PAR interactions. High ratios of PAR/UV-B and UV-A/UV-B have been found to be important in ameliorating UV-B damage. Growth chamber and greenhouse studies conducted at low PAR, low UV-A, and high UV-B often show exaggerated UV-B damage. In general, one observes a reduction in total biomass and plant height and a shift in biomass allocation pattern with decreasing PAR and increasing UV-B. There is some evidence that the primary damaging effect of UV-B is not on photosystem II reaction centers but on some component of the Calvin cycle and that high PAR protection is conferred by this component rather than by the activity of UV repair enzymes (photolyase). The protective effects of high PAR against elevated UV-B may also be indirect, by increasing leaf thickness and the concentration of flavonoids, known to be important in UV screening. The quality of PAR is also important, with blue light, together with UV-A radiation playing a key role in photoreactivation. Native species appear to be more resistant to elevated UV-B than crop plants in terms of biomass reduction, but both groups may show subtle changes in shoot elongation and leaf size. These morphological changes may have important consequences for natural ecosystems by altering the competitive balance in mixed communities, with more UV-resistant species replacing UV-sensitive ones. |
