The stratospheric ozone depletion and enhanced solar ultraviolet-B (UV-B) irradiance may have adverse impact on living organisms. The impact of UV-B radiation (UV-B, 280~320nm) on growth, biochemical and antioxidant enzyme activity was studied in Indigofera tinctoria (L.) seedling, commonly used as a green manure. The supplementary UV-B radiation significantly decreased the growth, development and changes in UV-B absorbing compounds such as anthocyanin and flavonoids. The antioxidant enzymes were unaffected and showed an enhanced activities of peroxidase, superoxide dismutase, polyphenoloxidase and phenylalanine ammonia-lyase except catalase in UV-B irradiated seedling. Indigofera tinctoria seedling tries to counteract high level of reactive oxygen species produced under UV-B stress through the increased activities of antioxidant enzyme. The results suggest that Indigofera tinctoria is resistant to UV-B radiation damage and the possible negative effect of additional UV-B radiation on the growth of seedling may have been effectively balanced by the UV-B radiation stress through increase in UV-absorbing compound and antioxidant enzymes.

Field studies were conducted to determine the role of defense mechanism in various parameters associated with plant protection subjected to UV-B radiation in Phaseolus trilobus Ait. commonly used as green manure and fodder. Spectrophotometric analysis showed that UV-B radiation decreases the chlorophyll content and increased the amount of UV-B absorbing compounds such as anthocyanins and flavonoids. Other UV-induced alterations included reduction in fresh weight and leaf area. However, wrinkling of leaves and increased leaf thickness was observed in UV-B treated seedlings. The antioxidant enzymes were unaffected and showed enhanced activity, except catalase in UV-B treated seedlings. These results suggest that, in general, UV-B radiation caused oxidative damage. However, plants have evolved complex mechanisms to scavenge the active oxygen species and thereby protect the cellular membrane, pigment and organelle.Key Words: Anthocyanin, catalase, chlorophyll, phenol, superoxide dismutase, UV-B radiation RÉSUMÉDes études sur le terrain ont été conduites pour déterminer le rôle du mécanisme de défense dans divers paramètres liés à la protection des plantes soumises au rayonnement UV-B dans le Phaselus trilobus Ait. communement utilisé comme engrais verts et fourrage. L'analyse spectrophotométrique a prouvé que le rayonnement UV-B diminue le contenu en chlorophylle et augmente la quantité de composés absorbant l'UV-B tels que des anthocyanines et des flavonoïdes. D'autres altérations d'UV-induits ont inclus la réduction de poids à l'état frais ainsi que de la surface foliaire. Cependant, on a observé des feuilles ridées et un accroissement en épaisseur de feuilles des plantules traitées par UV-B. Les enzymes antioxydantes n'étaient pas affectées et ont montré une augmentation de leur activité, à l'exception de la catalase dans les plantules traitées au UV-B. Ces résultats suggèrent que, en général, le rayonnement UV-B cause le dommage oxydative. Cependant, les plantes ont développé des mécanismes complexes pour se débarrasser des espèces d'oxygène actif et ainsi protéger la membrane cellulaire, le pigment et organelle.

BALAKRISHNAN V., VENKATESAN K., RAVINDRAN K.C., KULANDAIVELU G. (2005): Protective mechanism in UV-B treated Crotalaria juncea L. seedlings. Plant Protect. Sci., 41: 115-120.There is concern that some anthropogenic atmospheric pollutants may result in a global reduction of stratospheric ozone. This would undoubtedly increase the level of ultraviolet radiation reaching the surface of the earth, which might have important biological consequences. The antioxidant defence system of a plant consists of a variety of antioxidant molecules and enzymes. The role of antioxidant enzyme activities in Crotalaria juncea under control without UV-B treatment and ultraviolet-B supplemental radiation (UV-B) was investigated. UV-B treatment for 6 h for 4 days resulted in severe inhibition in catalase activity. On the other hand, the activities of peroxidase, polyphenol oxidase, superoxide dismutase and phenylalanine ammonialyase increased after the UV-B treatment when compared to control seedlings. These increases could be an adaptive mechanism to minimise the effects of UV-B radiation. Keywords: Crotalaria juncea L.; UV-B radiation; antioxidant; catalaseAbbreviations: UV-B -Ultraviolet-B; O 2 -,-Oxyradical; PVP -Polyvinyl pyrolidone 116Vol. 41, decreased stem length, leaf area and plant height in cucumber, sunflower, soybean and loblolly pine (TEVINI & TERAMURA 1989). Reduction in biomass accumulation resulting from increased UV-B radiation was observed in wheat, barley, soybean, tomato, cucumber and lettuce (KRUPA & KICKERT 1989). However, defence mechanisms such as foliar symptoms like curling of leaves and shiny wax coating (NEDUN-CHEZHIAN & KULANDAIVELU 1996), synthesis of phenolic substances such as anthocyanin and flavonoids (RAVINDRAN et al. 2001) and synthesis of antioxidant enzymes like peroxidase, polyphenol oxidase and superoxide dismutase (RAO et al. 1996) have been observed in UV-B treated Arabidopsis thaliana seedlings. Many plants possess very efficient scavenging systems for reactive oxygen that protects them from destructive oxidative reactions (ARORA et al. 2002). UV-B radiation increases the production of reactive oxygen species (H 2 O 2 , O 2 -, OH − ). These oxygen species are extremely reactive and have a cytotoxic nature (BOWLER et al. 1992). Plants have evolved protective mechanisms to keep these deleterious reactions to a minimum. Antioxidative enzymatic defence includes catalase, peroxidase and superoxide dismutase. Polyphenol oxidase and phenylalanine ammonialyase also participate in protection via phenolic compounds. These enzymes can mitigate the UV-induced damage by protecting the photosynthetic pathway and cellular components. The present study was conducted to determine the role of antioxidant defence mechanism in UV-B treated seedlings of Crotalaria juncea L., a plant widely cultivated in South India as green manure. MATERIALS AND METHODS Plants.Pre-soaked seeds of Crotalaria juncea were germinated in the dark for 2 days and then transferred to indirect daylight in the laboratory. Af...

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Changes in photosystem (PS) 2 activity were measured in Anacystis nidulans cells exposed to UV-B irradiation. The decrease in PS 2 activity was biphasic in cells exposed at the surface (0 cm) and at 2 cm depth in the water column, while gradual in those exposed at 10 and 30 cm depth. Addition of supplemental "white light" reduced the extent of UV-B damage. Decrease in photosynthetic activity was primarily due to the loss of energy transfer from phycobilisome to chlorophyll as the former in cyanobacteria acts as the primary light-harvesting complex. This was supported by the absorption and fluorescence excitation and emission spectral studies. All these changes were proportionally reduced by the thickness of the water column that reduced UV-B irradiance.

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Changes in various components of photosynthetic apparatus during the 4 d dark incubation at 25 ~ of detached control and ultraviolet-B (UV-B) treated Vigna unguiculata L. leaves were examined. The photosynthetic apparatus was more degraded in younger control seedlings and for a longer time UV-B treated seedlings than in the older or for a shorter time UV-B treated seedlings. This was shown by determining the losses in chlorophyll (Chl) and protein contents, variable fluorescence yield, photosystem (PS)2, PS1 and ribulose-l,5-bisphosphate carboxylase (RuBPC) activities, and photosynthetic 14CO2 fixation. In contrast, the Car/Chl ratio increased during the dark incubation due to less expressed degradation of Car.

The operating potential of this chamber is determined by the optimisation of the efficiency and noise rate of the device. This optimisation is based on the assumption that the performance of the device over the whole surface area is uniform. The INO-ICAL experiment is going to use ∼ 30000 RPC of size ∼2 m×2 m. All the RPC will have to pass a minimum quality assurance criteria, but may not be able to maintain a good uniformity over the whole surface area, particularly for the whole running period of about twenty years. This paper describes the choice of the optimum operating HV for an RPC of non-uniform response.