Growth and Defense Metabolism of Plants Exposed to Ultraviolet-B Radiation

Abstract

Increases in ultraviolet (UV) radiation at the Earth's surface due to the depletion of the stratospheric ozone layer are major concern for researchers, posing interest in the mechanisms of various effects on organisms. Although UV radiation comprises only a small fraction of the total solar radiation that is incident at the earth's surface, it has the greatest energy per unit wavelength and, thus, the greatest potential to damage the biosphere. Intensified current and projected UV -B radiation is responsible for multiple detrimental effects on plant growth and metabolism via interfering with biological processes. In plants, these effects include lipid oxidation, DNA damage, protein destruction which often causes heritable mutations. High UV -B levels introduce DNA damage, number of different lesions, predominantly cyclobutane pyrimidine dimer and pyrimidine (6-4) pyrimidinone products in the genome. It affects physiological processes, including the photosynthetic apparatus; causes loss of crop yield and productivity. Plants developed a number of repair or tolerance mechanisms to counteract the damage caused by UV or any other stressors. Here we reviewed the structural and biochemical defense strategy of plants in response to Ultraviolet -B radiation. The major points are as follows (i) in brief focus on global scenario of ozone depletion and consequent trend of increase in UV -B irradiation level; (ii) Effect of UV -B on shoot morphology, canopy structure (anatomical changes) could alter the stand photosynthesis, attributed to loss of Biomass and yield (iii) UV -B might play role as a signal molecule to up -regulate the expression of gene involve in multiple developmental response i.e. photomorphogenic response and antioxidants defense (iv) Some kinds of UV -B screening pigments such as carotenoids, flavonoids protect plant cells against intensive penetration of UV -B radiation. (v) Activation of non enzymatic antioxidants as well as enzymes by the Ultraviolet -B factors is discussed.