Radish (Raphanus sativus L.) and carrot (Daucus carota L.), plants with underground storage organs grown in the field, were exposed to either ambient (UVA) or 20 % UV-B (UVE) enhanced solar radiation till their root yield stage. In radish, UVE produced a significant increase in shoot and root fresh mass (FM), increase in the contents of chlorophyll, carotenoids, flavonoids, and total proteins per unit FM, Hill reaction rate, and root yield. In contrast, carrot responded negatively to UVE showing a loss in the above parameters.

UV-B is a growing concern due to the rise in UV-B levels on the surface of the earth as a result of the loss of stratospheric ozone. Increased levels of UV-B radiation can in fact negatively alter plant physiological processes, growth and productivity. However, when researching the effects of UV-B on medicinal plants like Phyllanthus amarus and in the tropical area under field conditions, there are some curious phenomena have been discovered. Enhanced UV-B radiation has greatly improved the growth of P. amarus. The outcome of the photosynthetic pigment showed increased UV-B enhanced synthesis of Chlorophyll or the accumulation of Chlorophyll pigments in the treated plants compared to non UV-B treated plants. The concentration of UV-B absorbing pigments also increased due to enhanced UV-B radiation in P. amarus. The synthesis of secondary metabolites such as flavonoid and phenol content was increased under UV-B treatment as compared to control. The UV-B radiation enhances the grade of the medicinal plant by improving the medicinally active compounds. This enhanced impact of UV-B could be important to observe when studying the phytotherapeutic function of P. amarus in health aspects of human life.

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The deleterious effects of ultraviolet B (UV-B) radiation on photosynthesis and photosynthetic proteins of tropical and temperate plants have been studied. Like tropical plants (black gram and green gram), the temperate plants (carrot and radish) also successfully grown in the tropical region. They were exposed to enhanced UV-B radiation under field condition. Comparative studies show that under enhanced UV-B radiation photosynthetic activity was increased in black gram. In green gram and radish the UV-B radiation slightly enhanced the photosynthetic activity, but it inhibited the photosynthetic activity in carrot. The comparative results showed changes in contents of thylakoid 55,47,43,33,29,23 and 17 kDa polypeptides that were significantly lowered in UV-B treated carrot plant when compared to other plants. The PSII protein profile results showed a strong correlation between the presence of a membrane polypeptide and photosynthetic activity. In black gram and green gram the UV-B radiation did not produce any significant difference in the PSII polypeptides. As in the case of radish the UV-B radiation increased the accumulation of 33-28 kDa protein and affected expression of the 63 kDa protein. In the case of carrot, severe degradation of 32 kDa and 33 kDa, corresponding to D1 and D2 core proteins of PSII, was observed. It could be concluded that the ability of plants to tolerate increased levels of UV-B radiation, relative to photosynthetic capacity, depends on acclimation processes of the plant in the growing region.Corresponding author: Shanthi Natarajan, Ph.D., research field: plant stress physiology. nowadays, since it includes the shortest wavelengths able to reach earth surface and thus it is the most dangerous for the living beings. The UV radiation in the long wavelength range, UV-A, 320-400 nm, possesses low energy and is quite harmless [1]. The emission of UV-B radiation not uniform throughout the earth surface it varied from low to high latitude. India is one among countries that are close to the equator, thus faces high fluxes of UV radiation with sunlight. The average latitude of India is 20 °C north of the equator and maximum UV-B (280-320 nm) irradiance near the equator (solar elevation angle < 25 °C) under clear, sunny skies is approximately 2.5Wm-2, which may affect the plants function. The plants are unavoidably exposed to UV-B due to the