Photosynthetic response of clusterbean chloroplasts to UV-B radiation: Energy imbalance and loss in redox homeostasis between QA and QB of photosystem II |
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Authors: | Padmanava Joshi Sasmita Gartia Manoj Kumar PradhanBasanti Biswal |
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Affiliation: | a Laboratory of Biophysics and Biochemistry, Anchal College, Padampur, Rajborasambar, Bargarh, 768036 Orissa, India b Laboratory of Biophysics and Biochemistry, School of Life Sciences, Sambalpur University, Jyotivihar, Sambalpur, 768019 Orissa, India |
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Abstract: | The effects of ultraviolet-B (UV-B: 280-320 nm) radiation on the photosynthetic pigments, primary photochemical reactions of thylakoids and the rate of carbon assimilation (Pn) in the cotyledons of clusterbean (Cyamopsis tetragonoloba) seedlings have been examined. The radiation induces an imbalance between the energy absorbed through the photophysical process of photosystem (PS) II and the energy consumed for carbon assimilation. Decline in the primary photochemistry of PS II induced by UV-B in the background of relatively stable Pn, has been implicated in the creation of the energy imbalance. The radiation induced damage of PS II hinders the flow of electron from QA to QB resulting in a loss in the redox homeostasis between the QA to QB leading to an accumulation of QA−. The accumulation of QA− generates an excitation pressure that diminishes the PS II-mediated O2 evolution, maximal photochemical potential (Fv/Fm) and PS II quantum yield (ΦPS II). While UV-B radiation inactivates the carotenoid-mediated protective mechanisms, the accumulation of flavonoids seems to have a small role in protecting the photosynthetic apparatus from UV-B onslaught. The failure of protective mechanisms makes PS II further vulnerable to the radiation and facilitates the accumulation of malondialdehyde (MDA) indicating the involvement of reactive oxygen species (ROS) metabolism in UV-B-induced damage of photosynthetic apparatus of clusterbean cotyledons. |
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Keywords: | Chl, chlorophyll Car, carotenoid DCMU, 3-(3,4dichlorophenyl)-1,1-dimethylurea Fm, maximum fluorescence Fv, variable fluorescence Gs, stomatal conductance K3Fe(CN)6, potassium ferricyanide MDA, malondialdehyde PAR, photosynthetically active radiation Pn, the rate of carbon assimilation QA, primary quinone electron acceptor of PS II QB, secondary quinone electron acceptor of PS II qp, photochemical quenching ROS, reactive oxygen species TL, thermoluminescence UV-A, ultraviolet-A (320-400 nm) UV-B, ultraviolet-B (280-320 nm) ΦPS II, quantum yield of PS II |
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