UV-B radiation

Equation 25 represents the reaction responsible for the removal of uv-B radiation (280—330 nm) that would otherwise reach the earth s surface. There is concern that any process that depletes stratospheric o2one will consequently increase uv-B (in the 293—320 nm region) reaching the surface. Increased uv-B is expected to lead to increased incidence of skin cancer and it could have deleterious effects on certain ecosystems. The first concern over depletion was from NO emissions from a fleet of supersonic transport aircraft that would fly through the stratosphere and cause reactions according to equations 3 and 26 (59) ... 

Comparison with other Studies. How do the results of our investigation compare with similar studies Our results corroborate the data provided in a similar study of the effect of UV-B on primary productivity in the southeastern Pacific Ocean (35). In the latter study, it was noted that enhanced UV-B radiation caused significant decreases in the productivity of surface and deep samples. Compared to ambient, primary productivity decreased with increasing doses of UV-B. In another study in which in situ experiments using natural Antarctic phytoplankton populations, it was noted that incident solar radiation significantly depressed photosynthetic rates in the upper 10-15 meters of the water column (36). It was also found that the spectral region between 305 and 350 nm was responsible for approximately 75 percent of the overall inhibitory effect. 

Although in this chapter we have focused on the potential effects of increased UV-B radiation on the Antarctic marine ecosystem, our results also have bearing on efforts to describe the effects of UV radiation on global marine productivity. However, here again, considerable uncertainties still remain in assessing the effects of ozone depletion on global production. Several authors have predicted a... 

Increased UV-B radiation decreased the rate of photosynthesis and changed pigment concentration. 

High temperature stress Low temperature stress High winds Global warming Increased UV-B radiation... 

The term CFCs is a general abbreviation for ChloroFluoroCarbons. They have been extensively used since their discovery in the thirties, mainly as refrigerant, foam blowing agent, or solvent because of their unique properties (non toxic, non flammable, cheap). However, after the first warning of Rowland and Molina [1] in 1974 that CFCs could destroy the protective ozone layer, the world has moved rapidly towards a phase-out of CFCs. Because the destruction of stratospheric ozone would lead to an increase of harmful UV-B radiation reaching the earth s surface, the production and use of CFCs is prohibited (since January 1, 1995 in the European Union and since January 1, 1996 worldwide). 

Giuntini, D., G. Graziani, B. Lercari et al. 2005. Changes in carotenoid and ascorbic acid contents in fruits of different tomato genotypes related to the depletion of UV-B radiation. J. Agric. Food Chem. 53 3174-3181. 

Because it is the UV-B radiation (280-320 nm) that causes the degradation, the absorption spectra of the UV-absorber must coincide with these wavelengths. UV-A (320-400 nm) does not cause damage (it is not energetic enough) and UV-C (wavelength less than 280 nm) does not reach the troposphere (it is filtered out by ozone in the stratosphere). The problem is to find an additive that absorbs UV-B but does not have an absorption "tail" in the UV-A and visible wavelengths, and therefore would have a yellow appearance. 

Fig. 3.9. Photochemical formation and non-catalytic destruction of ozone. UV-C radiation (200-280 nm wavelength) UV-B radiation (280-320 nm wavelength). Note how high-quality energy (UV radiation) is converted into lower quality energy (heat). Catalysts such as freons or nitrogen oxides can destroy ozone (e.g. Cl + 03 —> CIO + 02).

Blaustein, A.R., P.D. Hoffman, J.M. Kiesecker, and J.B. Hays. 1996. DNA repair activity and resistance to solar UV-B radiation in eggs of the red-legged frog. Conserv. Biol. 10 1398-1402. 

UV-b radiation has wavelengths in the range 290-320 nm. It is much more dangerous to the skin than UV-a because each photon possesses more energy. In consequence, the photolytic processes caused by UV-b are more extreme than those caused by UV-a. For example, UV-b causes thermal degradation of the skin (we call it sunburn ) but, additionally, it inhibits DNA and RNA replication, which is why over-exposure to UV-b will ultimately lead to skin cancer. 

Pavia H, Cervin G, Lindgren A, Aberg P (1997) Effects of UV-B radiation and simulated herbivory on phlorotannins in the brown alga Ascophyllum nodosum. Mar Ecol Prog Ser 157 139-146 Pawlik JR (1993) Marine invertebrate chemical defenses. Chem Rev 93 1911-1922 Pettit GR, Kamano Y, Herald CL, Tuinman AA, Boettner FE, Kizu H, Schmidt JM, Baczynskyj L, Tomer KB, Bontems RJ (1987) The isolation and structure of a remarkable marine animal antineoplastic constituent dolastatin 10. J Am Chem Soc 109 6883-6885 Pfander H, Stoll H (1991) Terpenoid glycosides. Nat Prod Rep 8 69-95... 

Pavia H, Cervin G, Lindgren A, Aberg P (1997) Effects of UV-B radiation and simulated her-bivory on phlorotannins in the brown alga Ascophyllum nodosum. Mar Ecol Prog Ser 157 139-146... 

Bischof K, Peralta G, Krabs G, van de Poll WH, Perez-Llorens JL, Breeman AM (2002) Effects of solar UV-B radiation on canopy structure of Ulva communities from Southern Spain. J Exp Bot 53 2411-2421... 

Bischof K, Janknegt PJ, Buma AGJ, Rijstenbil JW, Peralta G, Breeman AM (2003) Oxidative stress and enzymatic scavenging of superoxide radicals induced by solar UV-B radiation in Ulva canopies from southern Spain. Sci Mar 67 353-359... 

Gotz T, Windhovel U, Boger P, Sandmann G (1999) Protection of photosynthesis against UV-B radiation by carotenoids in transformants of the cyanobacterium Synechococcus PCC7942. Plant Physiol 120 599-604... 

The raison d etre for the proliferation of flavone and flavonol glycosides in nature continues to intrigue plant scientists. The ability of UV-B radiation to damage DNA, RNA, and proteins as well as to impair processes like photosynthesis is well known. Most flavonoids are very efficient antioxidants and chemoprotectants, and are therefore used in a plethora of food supplements and nutraceuticals [30]. Some flavonoids, however, have a Janus face - they could be excellent antioxidants but also have negative features. 

FIGURE 8.2 Formation of a thymine-thymine dimer by UV-B radiation, and repair by UV-A or blue light-activated photolyase. 

Balakumar, T., Babu, V.H.B., and Paliwal K., On the interaction of UV-B radiation (280-315nm) with water stress in crop plants, Physiol. Plant., 87, 217, 1993. 

Mendez, M., Jones, D.G., and Manetas, Y., Enhanced UV-B radiation under field conditions increases anthocyanin and reduces the risk of photoinhibition but does not affect growth in the carnivorous plant Pinguicula vulgaris. New Phytol, 144, 275, 1999. 

Bacci, L. et al., UV-B radiation causes early ripening and reduction in size of fruits in two lines of tomato Lycopersicon esculentum Mill.), Glob. Change Biol, 5, 635, 1999. 

Bomman, J.F. and Vogelmann, T.C., Effect of UV-B radiation on leaf optical properties measured with fibre optics, J. Exp. Bot., 42, 547, 1991. 

Burchard, P., Bilger, W., and Weissenbock, G., Contribution of hydroxycinnamates and flavonoids to epidermal shielding of UV-A and UV-B radiation in developing rye primary leaves as assessed by ultraviolet-induced chlorophyll fluorescence measurements, Plant Cell Environ., 23, 1373, 2000. 

Day, T.A., Relating UV-B radiation screening effectiveness of foliage to absorbing-compound concentration and anatomical characteristics in a diverse group of plants, Oecologia, 95, 542, 1993. 

Laakso, K., Sullivan, J.H., and Huttunen, S., The effects of UV-B radiation on epidermal anatomy in loblolly pine Pinus taeda L.) and Scots pine (Pinus sylvestris L.), Plant Cell Environ., 23, 461, 2000. 

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