title: High light intensity augments mercury toxicity in cyanobacterium Nostoc muscorum.
abstract: The present study is aimed at investigating the role of growth irradiance in determining the extent of mercury (Hg) toxicity on various physiological parameters viz. growth, pigment contents, photosynthesis, respiration, (14)CO(2) fixation, photosynthetic electron transport, photorespiration and enzyme activity of cyanobacterium Nostoc muscorum. A general decline was observed in all these parameters with increasing concentration of Hg except for carotenoids content and respiratory activity which exhibited significant enhancement. This effect was more pronounced in high light (130 μmol photon m(-2) s(-1)) exposed cells as compared to normal (70 μmol photon m(-2) s(-1)) and low (10 μmol photon m(-2) s(-1)) light exposed cells. Among the photosynthetic electron transport activities, whole chain was found to be more sensitive than photosystem II (PSII) and photosystem I (PSI). (14)CO(2) fixation was more affected as compared to O(2) evolution when exposed to Hg and different light intensities. Photorespiratory activity, which is an index of protecting organisms from light-induced damage, also showed a similar declining trend. Enzyme assay revealed that among the carboxylating enzymes, activity of RUBISCO was more severely inhibited than PEPCase. Thus, these results suggest that Hg itself was toxic at all tested concentrations and high light intensity augmented its toxicity in N. muscorum inhibiting the growth, pigment contents and photosynthetic activity of the organism.
authors.affiliation: Ranjan Plant Physiology and Biochemistry Laboratory, Department of Botany, University of Allahabad, Allahabad, 211 002, UP, India. vermaranjana09@gmail.com
authors.forename: Ranjana
authors.initials: R
authors.lastname: Singh
authors.forename: Gunjan
authors.initials: G
authors.lastname: Dubey
authors.forename: Vijay Pratap
authors.initials: VP
authors.lastname: Singh
authors.forename: Prabhat Kumar
authors.initials: PK
authors.lastname: Srivastava
authors.forename: Sushil
authors.initials: S
authors.lastname: Kumar
authors.forename: Sheo Mohan
authors.initials: SM
authors.lastname: Prasad
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D008027:Light; D008628:Mercury / Q000633:toxicity*; D050502:Nostoc muscorum / Q000187:drug effects* / Q000528:radiation effects*; D010788:Photosynthesis / Q000187:drug effects; D045331:Photosystem I Protein Complex / Q000187:drug effects; D045332:Photosystem II Protein Complex / Q000187:drug effects
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002245:Carbon Dioxide; D008628:Mercury