CHAPTER ONE

INTRODUCTION

Background of Study

In 1973, a panel of scientists reported to the Environmental Studies Board that there was a need for research on the effects of ultraviolet (UV) light on food crops (National Academy of Science, 1973). The scientific community was, at the time, worried about how pollution from supersonic transport aircrafts could thin the ozone layer and therefore affect life on earth. However, we now know that the decline in ozone is due to chlorine and bromine containing pollutants entering the atmosphere (Pyle, 1997). Research into the effects of deceased ozone in the atmosphere has continued since the 1970s.

For life to leave the seas and begin on land, primitive plants had to evolve mechanisms to protect themselves from UV radiation. To this day, some algae and even photosynthetic bacteria lack complex flavonoids and instead have other UV-screening compounds (Rozema et al., 2002). These include mycosporine-like amino acids (MAAs) and scytonemins, which filter out UV-C radiation and are only found in cyanobacteria. MAAs and scytonemins can be considered primitive forms of plant protection, since UVC is unable to penetrate the ozone layer (Rozema et al, 2002). Similar to flavonoids and carotenoids in terrestrial plants, these compounds perform other functions, such as the role of MAAs in reducing freeze damage in alga cells.

Plants are liable to be exposed to various abiotic and biotic stress factors throughout their life time, yet same of them can adapt to changing environmental by different morphological, physiological and chemical means (Walling, 2000 and Diaz et al., 2007). The decrease in stratospheric ozone and the resulting increase of solar ultraviolet have become a general worldwide concern in the last few decades. Solar ultraviolet radiation is highly dynamic abiotic environmental factor of major importance, which serves as an essential cue for growth and differentiation processes in plants (Paul and Gwynn-Jones, 2003). Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than soft X-rays. It can be subdivided into near UV (380-200 nm wave length) and extreme or vacuum UV (200-10 nm). The range of UV wavelength is often subdivided into UV-A (380-315 nm), called long wave or black light; UV-B (315-280nm); called medium wave; and UV-C (280-10 nm) called short wave or germicidal. The V-UV and UV-C to the solar spectral irradiance is low, their ability to cause biological damage is high because of the energies associated with these short wave lengths. When plants are not acclimatized or are irradiated with UV level above the current ambient radiation, this radiation can have detrimental effects on proteins, lipids and specifically affect the photosystem by damaging its membranes and decreasing enzyme activities and photosystem rates (Rozema et al., 1997; Sullivan et al., 2003 and Bassman, 2004). Many fruits, flowers and seeds stand out more strongly from the background in ultraviolet wavelengths as compared to human. The plant seeds are stored desiccated under conditions of low temperature and vacuum. Solar UV irradiation had the most deleterious effect on organisms (Horneck, 1993 and Horneck et al., 1995). Numerous studies have demonstrated that increased UV-B can directly or indirectly affect the growth of plants (Joshi et al., 2007 and Feng et al., 2007). Relatively little information was available on the effect of VU radiation on forest tree species (UNEP, 1998). Tropical forests, though representing nearly one half of global productivity and much of the total tree species diversity, have received very little attention with respect to the ozone reduction problem. There is some information for mid-temperate latitude tree species; because they are long-lived trees present the opportunity to observe the longer-term cumulative effects of UV-B exposure over several years for the same individuals (UNEP, 1998). A few studies have been undertaken to investigate the effects of UV radiation on tree seeds germination and chlorophyll concentration.

1.2 Objectives of Study

1.      Effect of Ultraviolet light and exposure periods on seeds germination

2.      Effect of Ultraviolet light and exposure periods on Chlorophyll concentration

1.3 Scope of Study

The study which aim at finding the effect of ultraviolent light on plant development will focus on using ultraviolent C. The study made use three plant samples from three different trees namely; Daucus carotais, Zea mays, Brassica oleracea var. capitata and Lactuca sativa

1.4 Significance of Study

The study will contribute to existing literature since there are no much work on this study. The study will aim farmers and other related professions to know the usefulness of ultraviolent light on food production.

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