EFFECTS OF ULTRAVIOLET RADIATION ON CYTOLOGICAL AND MOLECULAR ASPECTS OF TOMATO

Abstract

Measurement of ozone level proved that stratospheric ozone layer is being depleted as a result of contamination with man-made chloroflurocarbon. One component of global climate change is the loss of stratospheric ozone which protects the earth from UV radiation. UV is traditionally divided into three wave-length ranges: UV-A, UV-B and UV-C. UV-C radiation is completely absorbed by atmospheric gases. UV-B is additionally absorbed by stratospheric ozone and thus only a very small proportion is transmitted to the earth's surface, whereas UV-A radi-ation is hardly absorbed by ozone. Organisms on earth are adapted to UV-A, but may not be adapted to UV-B. Now and due to the reduction in atmospheric ozone, a great deal of attention has been focused on UV-B induced photo damage organisms. A 10% decline in the total stratospheric ozone would raise the amount of UV-B reaching the earth’s surface by 20%. UV radiation has been shown to be harmful to living organisms, damaging DNA, lipids, protein and membrane. Plants, which use sunlight for photosynthesis, cannot avoid exposure to increased levels of UV radiation so they are at higher risk. In order to understand the significance of change of climate to increased UV-B radiation. Our work has demonstrated the severe effect of UV on tomato cytological parameters as well as on the level of DNA using different molecular marker assays. Tomato seeds (Castle Rock variety) were germinated, then at age of three weeks; they were exposed to UV-B radiation during 0, 20, 40 and 60 min periods. Mitotic abnormalities and mitotic index were analyzed. Exposure to UV-B radiation slightly affected the mitotic index but induced both clastogenic and aneugenic effects. UV-B radiation increased the fre-quency of mitotic abnormalities in a time-dependent manner. Changes in DNA fin-gerprint was monitored in UV irradiated seedlings using RAPD, ISSR and SCoT molecular marker assays. The DNA of the irradiated tomato plants and control were assessed using 11 RAPD, 19 ISSR and 15 SCoT primers.These primers produced 119, 130 and 182 amplicons, respectively. The numbers of polymorphic amplicons were 65, 46 and 78; corresponding to a level of polymorphism 54.6, 35.4 and 43.0%, respectively. The dendrograms obtained using these marker types efficiently separate different duration irradiated plants and control in two clusters except RAPD dendrogram. The data scored from RAPD, ISSR and SCoT were combined and computed to generate more accurate relationships based on large and versatile genome coverage. The combined dendrogram clearly separated irradiated plants and control ones into two separate clusters; which is in a good agreement with both ISSR and SCoT dendrograms.