Moderate UV-B Research Articles

UV damage and photoreactivation potentials of larval shrimp, Pandalus platyceros, and adult euphausiids, Thysanoessa raschii.

Previously reported thresholds for UV-B dose and dose-rate were determined under artificial light regimes using more than an order of magnitude less visible light than found naturally. Near-UV and/or visible light is needed for photoreactivation, and the accuracy of earlier findings may have been influenced by less than maximum photorepair in the laboratory. Experiments with shrimp larvae and adult euphausiids, comparing survival at various UV-B doses and dose-rates combined with different levels of near-UV and visible irradiance, suggest that photorepair occurs in these organisms. Further, this apparent photorepair reaches maximum levels at relatively low visible light intensities.Previously reported tolerance limits for shrimp larvae and adult euphausiids were confirmed (in particular, the relationship between dose/dose-rate safe and lethal limits in shrimp). Also, the earlier experimental design did not appear to have affected these limits since additional near-UV and visible light did not substantially alter the results.In experiments using a 44-1 plastic cylinder (140-cm water depth), adult euphausiids successfully avoided moderate UV-B combined with visible light, but were attracted to and ultimately killed by higher levels of UV-B combined with low visible light. The apparent inability of euphausiids to directly detect harmful levels of UV-B irradiance would become an important factor in a new solar spectral distribution caused by ozone depletion.

Effects of Enhanced UV-B Radiation on Germination, Seedling Growth, Leaf Anatomy and Pigments of Some Crop Plants

Summary Cucumis sativus , Phaseolus vulgaris and Raphanus sativus seedlings were continuously irradiated with different levels of UV-B by using cut-off filter systems at a constant irradiance of visible light for up to 12 days. The rate of germination decreased under the highest UV-B irradiance to about 60% of the value of control seeds irradiated with small amounts of UV-B. With rising UV-B levels the growth of hypocotyls was increasingly inhibited. In Cucumis even the lowest level of UV-B irradiation prevented the elongation of hypocotyls. Fresh weight, dry weight and leaf area were smaller in all plants exposed to UV-B. The greatest effect was obtained on leaf area whereas dry weight was only slightly decreased. The contents of photosynthetic pigments were reduced to a similar extent as leaf area. Accumulation of flavonoids increased in radish seedlings, but decreased in cucumber and bean seedlings. Thickness of abaxial and adaxial epidermis of cucumber cotyledons was reduced, whereas the palisade parenchyma became thicker. The leaf surface structure was progressively damaged with increasing UV-B irradiance as shown by SEM pictures. The stomatal number on both sides was markedly lower in UV-B irradiated cucumber cotyledons. Enhanced levels of UV-B irradiation caused reduced growth and pigment accumulation in all plant species investigated. Cucumis, as the most UV-B sensitive plant, was already markedly affected by moderate UV-B irradiation levels.

Ultraviolet-B Radiation-induced Inhibition of Leaf Expansion and Promotion of Anthocyanin Production

Leaf discs from expanding leaves of Rumex patientia L. were exposed to 7 hours of visible plus different levels of ultraviolet radiation in the 290 to 315 nm waveband (UV-B) and then placed in darkness. Leaf disc expansion was reduced and anthocyanin production was increased in discs exposed to moderate or high levels of UV-B radiation when compared to control discs. The possibility that the inhibition of leaf expansion by UV-B radiation might be at least partially phytochrome-mediated was examined by giving discs brief red or far red irradiation following exposure to UV-B radiation. Brief red radiation (R) following treatment with moderate or high UV-B radiation did not alter the pattern of growth or anthocyanin production compared to discs placed in darkness following UV-B treatment. However, a posttreatment with far red radiation (FR) reduced the growth of discs subjected previously to either moderate UV-B or no UV-B irradiation to the level of growth of discs given high UV-B. FR posttreatment also decreased anthocyanin production in discs in moderate and high UV-B treatments. Effects of FR and UV-B radiation apparently do not involve the same mechanism. This was demonstrated by experiments in which FR following the UV-B treatments was in turn followed by R, which reversed the effects of the FR but did not alter the growth inhibition or increased anthocyanin production induced by moderate or high levels of UV-B radiation.