Effect of UV Radiation on Life Forms

Abstract

Since the development of life-supporting atmosphere on earth and subsequent establishment of life on earth life forms have adjusted with the extent of solar UV radiation fluencing on earth through the straospheric ozone layer – the adjustment exhibiting correlation with locational/seasonal variation in intensity of UV fluence. Earlier in evolution, to avoid the high UV radiation prevalent in earth’s atmosphere at the time when the stratospheric ozone protection was not in place, early life forms remained under oceanic water protection and migrated to terrestrial habitat only after the protective ozone layer was well established. Communities of life forms correlated with location (latitude/altitude) based variation in UV fluence became established only after development of (a) genetically controlled accumulation of internal protective compounds viz. phenolics allowing UV acclimation as well as protection from ravages of insects and animals on plants bringing about (b) development of molecular/physical interdependence among the different life forms on earth; balanced co existence among life forms was thus established. Since the later part of the last century, thinning of the stratospheric ozone layer causing enhanced UV radiation (in the post “ozone hole” era) has adverse anthropogenic activity related thinning of the stratospheric ozone layer has caused enhanced UV fluence on earth (in the post ‘ozone hole’ era) bringing about threats of a breach in this balanced state of survival of life forms on earth. Bearing in mind that interaction between components, in a community viz., plants, pests, pathogens, insects, and animals, in a community determines survival potential of life on earth and that each life form is differentially affected by UV radiation, a comprehensive understanding on the effect of UV radiation on earth and UV related interaction between life forms in ecosystems would be a worthwhile study.

It is pertinent to mention that UV-B radiation, due to its high energy corresponding to its short wavelength (280–315 nm), threatens survival of life on earth. In the terrestrial ecosystem, UV-B fluence in open field is potentially detrimental to all living forms – the extent of damaging effect exhibiting varietal difference. Terrestrial plant habitats are varied and include agricultural lands, forests, grasslands, marsh land, savannahs, deserts, tundra, etc. The importance of interactions among plant species and also other components like microbes, pests, insects, animals, etc. in determining the structure and dynamics of terrestrial life forms in communities is widely recognized. Functioning of these ecosystems involves many attributes that could potentially be affected by increased solar UV radiation, including plant biomass production, seed production, plant consumption by herbivores including insects, and disease incidence of plants and animals. Studies are also available on effect of UV on crop plants – the findings indicate variations in survival and productivity due to status of internal acclimation strategy, subject to function of genetic makeup in the plant under study. Biodiversity loss of UV-sensitive varieties as an outcome also of seed viability loss during post harvest survival persistence of orthodox seed is another harmful consequence of enhanced UV fluence.

Aquatic ecosystems are safer (in comparison to terrestrial ecosystems) due to the additional protection provided by the UV shielding property of water bodies – the extent of UV protection varying with depth of water column and concentration of dissolved organic matter. The effect relates to UV absorption through water layer, modified by interfering turbidity and concentration of colorless or colored dissolved organic matter (DOM/CDOM). Some studies have also reported that enhanced UV radiation due to stratospheric ozone depletion is found to have deleterious effects on phytoplankton, algae, eggs, and larval stages of fish and other aquatic animals. Phytoplanktons are of particular interest as this group of organisms forms the basis of food chain in the oceanic ecosystems. Humans are also affected by the enhanced UV fluence, developing various types of lesions; common effects are DNA damage, retarded growth, lesions in eyes, and skin often leading to skin cancer. UV-induced upregulation of pigments, viz., melanin, that confer dark skin in human represents a UV acclimation strategy that protect against UV fluence. An exemplary situation is evidenced by the dark skin (due to melanin in epidermis) of natives in Africa and India; such traits constitute an evolutionary survival strategy against high UV radiation that is higher at lower latitudes (with high UV radiation) near the equator. A protective effect of UV on animals relates to upregulation of synthesis of vitamin D that is required for bone and muscle development and also for proper functioning of the immune system. The damaging and protective effect of UV observed in animals is comparable to that observed in plants. However, the protective effect in plants is relatively more developed as would be expected because plants have to endure the brunt of UV radiation through stationary lifestyle in open field.

Development of survival strategy under UV radiation evidenced in plants also relates to pigmentation, both colored (viz., anthocyanin) and colorless (viz., flavonoids) in the epidermis; these serve as UV-protective internal screens – the extent of protection exhibiting species specificity. UV-induced cell protective compounds in plants exhibit a greater/far-reaching protective effect, serving as natural antioxidants specifically produced in plants, and that through the dietary process also provide for natural antioxidant in animals that are devoid of cellular machinery for production of antioxidants.