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Banaras Hindu University (2016)

Ultraviolet B induced changes in selected medicinal plants

Takshak, Swabha

Titre : Ultraviolet B induced changes in selected medicinal plants

Auteur : Takshak, Swabha

Université de soutenance : Banaras Hindu University

Grade : Doctor of Philosophy (PhD) 2016

Résumé partiel
1. Two major ground-breaking observations regarding ozone layer put forward its depletion as a matter of global concern. The first was that chlorofluorocarbons destroy ozone molecules, and the second was the discovery of the Antarctic ozone hole. Recent findings concluded that despite the successful implementation of Montreal Protocol to control the emissions of ozone depleting substances, the ozone hole is unlikely to recover to pre-1980 levels till mid-2070s. Consequently, UV-B levels reaching the Earth may continue to be harmful to all living organisms, including plants, especially in the tropics, where a small increase in UV-B intensity may affect the plants considerably. Moreover, in the coming years, the UV-B scenario is likely to be affected by other factors also, such as aerosols and cloud cover.
2. Since plants need to perform photosynthesis, they inevitably require sunlight and consequently are exposed to higher levels of UV-B. UV-B exposure has been known to cause changes in plants at morphological, biochemical, physiological, and genetic levels. General plant responses to UV-B include reduced plant height and biomass accumulation, reduced leaf growth and expansion, leaf chlorosis and necrosis, enhanced leaf epicuticular wax content and stomatal index, altered leaf thickness, increased tillering and branching, reduced pollen viability and pollen tube growth, altered quality and quantity of the economic product, accumulation of defence-related secondary metabolites in high concentrations, increased levels of antioxidative defence compounds, reductions in nitrate metabolism and nodulation in leguminous plants, inhibition of protein biosynthesis, adverse effects on photosynthetic apparatus and processes, and differential gene expression. However, the responses of plants to their environment are complex ; to UV-B also, these responses show high variability depending upon the dose and duration of UV-B radiation, crop species and different cultivars within the same species, and plant acclimation and adaptation levels depending upon prior exposure to UV-B.
3. The present study was conducted keeping supplemental UV-B (s-UV-B) within the purview of stress factor. It was aimed at evaluating the effects of s-UV-B on growth characteristics, physiological, and biochemical aspects of two medicinal plants, Withania somnifera and Coleus forskohlii. The former is known for its alkaloids while the latter is an essential oil yielding plant. s-UV-B-induced changes in plant-specific medicinal constituents (withanolode A and withaferin A in W. somnifera and essential oil content and composition in C. forskohlii) were also studied. In both these plants, roots are considered to be of commercial importance. Since roots are the economically important plant parts, and leaves are directly exposed to UV-B, the effects of this stress factor on various above mentioned parameters were evaluated in both the plant organs. W. somnifera (Solanaceae) is an erect, evergreen, branching perennial shrub used for the treatment of bronchitis, senile dementia, Alzheimer’s and Parkinson’s diseases, various neurological disorders, and tumours ; it is also used as an aphrodisiac, liver tonic, astringent, and therapeutic agent. C. forskohlii (Lamiaceae) is a perennial aromatic plant. It is used for treating asthma, bronchitis, insomnia, epilepsy, hypothyroidism, depression, psoriasis, spasms, skin and intestinal disorders, cancer, diabetes, heart diseases, and obesity, and regulation of blood pressure. The essential oil is also used commercially as a food-flavouring and antimicrobial agent

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