Introduction
Photosynthetic organisms need sunlight for preparing their food and are hence exposed to different kinds of harmful ultra violet radiations as well. These UV radiations are divided into three categories depending on the range of their wave length. The uv-c of 200 to 280nm are very harmful for the living organisms on the earth but not under the natural conditions. UV-B radiations of wavelength 280-320nm contributing 1.5% of the spectrum of light but has very harmful effects on the plants. UV-A of 320-400nm are contributing 6.3% of the incoming rays from the sun but are not very harmful. The light having wavelength greater than 290nm can only reach to the earth but because of many biotic and the anthropogenic activities there is depletion of ozone layer due to which the harmful radiation of smaller than the 290nm can also pass through the ozone filters and reaches to the earth imposing harmful effects on plants. UV-B radiation most harmful among all has many direct and indirect effects on plants, including damage to DNA, changes in proteins and membranes, in transpiration and photosynthesis alterations in growth, development and morphology. According to some studies there has been decrease in the biomass accumulation under the UV-B stress.
Target sites of the UV radiations
Nucleic acids
One of the most important target of the UV radiations is the DNA the UV-B and UV-C radiations have destructive effect on the DNA causing mutation in the replication process. The