title: Photosynthetic response of clusterbean chloroplasts to UV-B radiation: energy imbalance and loss in redox homeostasis between Q(A) and Q(B) of photosystem II.
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 (P(n)) 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 P(n), has been implicated in the creation of the energy imbalance(.) The radiation induced damage of PS II hinders the flow of electron from Q(A) to Q(B) resulting in a loss in the redox homeostasis between the Q(A) to Q(B) leading to an accumulation of Q(A)(-). The accumulation of Q(A)(-) generates an excitation pressure that diminishes the PS II-mediated O(2) evolution, maximal photochemical potential (F(v)/F(m)) and PS II quantum yield (Φ(PS 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.
authors.affiliation: Laboratory of Biophysics and Biochemistry, Anchal College, Padampur, Rajborasambar, Bargarh, 768036 Orissa, India. padmanava.joshi@gmail.com
authors.forename: Padmanava
authors.initials: P
authors.lastname: Joshi
authors.forename: Sasmita
authors.initials: S
authors.lastname: Gartia
authors.forename: Manoj Kumar
authors.initials: MK
authors.lastname: Pradhan
authors.forename: Basanti
authors.initials: B
authors.lastname: Biswal
mesh_terms: D002244:Carbon / Q000378:metabolism / Q000528:radiation effects; D002338:Carotenoids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism / Q000528:radiation effects; D002736:Chloroplasts / Q000502:physiology / Q000528:radiation effects; D018548:Cotyledon / Q000378:metabolism / Q000502:physiology / Q000528:radiation effects; D031293:Cyamopsis / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects*; D004579:Electron Transport / Q000528:radiation effects; D005419:Flavonoids / Q000378:metabolism; D008315:Malondialdehyde / Q000378:metabolism / Q000528:radiation effects; D010084:Oxidation-Reduction / Q000528:radiation effects; D010100:Oxygen / Q000378:metabolism / Q000528:radiation effects; D010788:Photosynthesis / Q000502:physiology / Q000528:radiation effects*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000502:physiology / Q000528:radiation effects*; D054046:Plant Stomata / Q000502:physiology / Q000528:radiation effects; D018526:Plant Transpiration / Q000502:physiology / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism / Q000528:radiation effects; D036226:Seedlings / Q000378:metabolism / Q000502:physiology / Q000528:radiation effects; D013816:Thermodynamics; D020524:Thylakoids / Q000378:metabolism / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D005419:Flavonoids; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D017382:Reactive Oxygen Species; D002734:Chlorophyll; D002338:Carotenoids; D008315:Malondialdehyde; D002244:Carbon; D010100:Oxygen