Abstract
The increase in ultraviolet-B (UV-B; 0.290-0.320 [mu]m) radiation received by plants due to stratospheric ozone depletion heightens the importance of understanding UV-B tolerance. Photosynthetic tissue is believed to be protected from UV-B radiation by UV-B-absorbing compounds (e.g. flavonoids). Although synthesis of flavonoids is induced by UV-B radiation, its protective role on photosynthetic pigments has not been clearly demonstrated. This results in part from the design of UV-B experiments in which experimental UV-A irradiance has not been carefully controlled, since blue/UV-A radiation is involved in the biosynthesis of the photosynthetic pigments. The relationship of flavonoids to photosynthetic performance, photosynthetic pigments, and growth measures was examined in an experiment where UV-A control groups were included at two biologically effective daily UV-B irradiances, 14.1 and 10.7 kJ m-2. Normal, chlorophyll-deficient, and flavonoid-deficient pigment isolines of two soybean (Glycine max) cultivars that produced different flavonol glycosides (Harosoy produced kaempferol, Clark produced quercetin and kaempferol) were examined. Plants with higher levels of total flavonoids, not specific flavonol glycosides, were more UV-B tolerant as determined by growth, pigment, and gas-exchange variables. Regression analyses indicated no direct relationship between photosynthesis and leaf levels of UV-B-absorbing compounds. UV-B radiation increased photosynthetic pigment content, along with UV-B-absorbing compounds, but only the former (especially carotenoids) was related to total biomass (r2 = 0.61, linear) and to photosynthetic efficiency (negative, exponential relationship, r2 = 0.82). A reduction in photosynthesis was associated primarily with a stomatal limitation rather than photosystem II damage. This study suggests that both carotenoids and flavonoids may be involved in plant UV-B photoprotection, but only carotenoids are directly linked to photoprotection of photosynthetic function. These results additionally show the importance of UV-A control in UV-B experiments conducted using artificial lamps and filters.
Full Text
The Full Text of this article is available as a PDF (1.1 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Assmann S. M., Grantz D. A. The magnitude of the stomatal response to blue light : modulation by atmospheric humidity. Plant Physiol. 1990 Jun;93(2):701–707. doi: 10.1104/pp.93.2.701. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Beggs C. J., Stolzer-Jehle A., Wellmann E. Isoflavonoid Formation as an Indicator of UV Stress in Bean (Phaseolus vulgaris L.) Leaves : The Significance of Photorepair in Assessing Potential Damage by Increased Solar UV-B Radiation. Plant Physiol. 1985 Nov;79(3):630–634. doi: 10.1104/pp.79.3.630. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mirecki R. M., Teramura A. H. Effects of Ultraviolet-B Irradiance on Soybean : V. The Dependence of Plant Sensitivity on the Photosynthetic Photon Flux Density during and after Leaf Expansion. Plant Physiol. 1984 Mar;74(3):475–480. doi: 10.1104/pp.74.3.475. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Pang Q., Hays J. B. UV-B-Inducible and Temperature-Sensitive Photoreactivation of Cyclobutane Pyrimidine Dimers in Arabidopsis thaliana. Plant Physiol. 1991 Feb;95(2):536–543. doi: 10.1104/pp.95.2.536. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sullivan J. H., Teramura A. H. Field Study of the Interaction between Solar Ultraviolet-B Radiation and Drought on Photosynthesis and Growth in Soybean. Plant Physiol. 1990 Jan;92(1):141–146. doi: 10.1104/pp.92.1.141. [DOI] [PMC free article] [PubMed] [Google Scholar]