Browsing by Author "Ahmed, Haseen"

Now showing 1 - 4 of 4
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    Physiological responses of the cyanobacterium Synechocystis sp. PCC 6803 under rhythmic light variations
    (Springer Nature, 2023) Singh, Prashant R.; Pathak, Jainendra; Rajneesh; Ahmed, Haseen; H�der, Donat-P.; Sinha, Rajeshwar P.
    Cyanobacteria are challenged by daily fluctuations of light intensities and photoperiod in their natural habitats, which affect the physiology and fitness of cyanobacteria. Circadian rhythms (CRs), an important endogenous process found in all organisms including cyanobacteria, control their physiological activities and helps in coping with 24-h light/dark (LD) cycle. In cyanobacteria, physiological responses under rhythmic ultraviolet radiation (UVR) are poorly studied. Therefore, we studied the changes in photosynthetic pigments, and physiological parameters of Synechocystis sp. PCC 6803 under UVR and photosynthetically active radiation (PAR) of light/dark (LD) oscillations having the combinations of 0, 4:20, 8:16, 12:12, 16:8, 20:4, and 24:24�h. The LD 16:8 enhanced the growth, pigments, proteins, photosynthetic efficiency, and physiology of Synechocystis sp. PCC6803. Continuous light (LL 24) of UVR and PAR exerted negative impact on the photosynthetic pigments, and chlorophyll fluorescence. Significant increase in reactive oxygen species (ROS) resulted in loss of plasma membrane integrity followed by decreased viability of cells. The dark phase played a significant role in Synechocystis�to withstand the�LL 24 under PAR and UVR. This study offers detailed understanding of the physiological responses of the cyanobacterium to changing light environment. � 2023, The Author(s), under exclusive licence to European Photochemistry Association, European Society for Photobiology.
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    Responses of a hot spring cyanobacterium under ultraviolet and photosynthetically active radiation: photosynthetic performance, antioxidative enzymes, mycosporine-like amino acid profiling and its antioxidative potentials
    (Springer Science and Business Media Deutschland GmbH, 2021) Ahmed, Haseen; Pathak, Jainendra; Rajneesh; Sonkar, Piyush K.; Ganesan, Vellaichamy; H�der, Donat-P.; Sinha, Rajeshwar P.
    This study summarizes the response of a hot spring cyanobacterium Fischerella sp. strain HKAR-14, under simulated light conditions of ultraviolet radiation (UVR), photosynthetically active radiation (PAR), PAR + UV-A (PA) and PAR + UV-A + UV-B (PAB). Exposure to UVR caused a decline in growth and Chl a while total carotene content increased under PA and PAB. Maximum photochemical efficiency of photosystem II (Fv/Fm) and relative electron transport rate decreased significantly in PA and PAB exposure. Higher non-photochemical quenching and lower photochemical quenching values were observed in UVR-exposed samples as compared to the control. Levels of intracellular reactive oxygen species (ROS) increased significantly in PAB and PA. Fluorescence microscopic images showed an increase in green fluorescence, indicating the generation of ROS in UVR. The antioxidant machinery including superoxide dismutase, catalase and peroxidase showed an increase of 1.76-fold and 2.5-fold superoxide dismutase, 2.4-fold and 3.7-fold catalase, 1.83-fold and 2.5-fold peroxidase activities under PA and PAB, respectively. High-performance liquid chromatography equipped with photodiode array detector, electrospray ionization mass spectrometry, Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy analyses reveal the occurrence of a single mycosporine-like amino acid, shinorine (?max 332.3 � 2�nm, m/z 333.1), with a retention time of 1.157�min. The electrochemical characterization of shinorine was determined by cyclic voltammetry. The shinorine molecule possesses electrochemical activity and represents diffusion-controlled process in 0.1�M (pH 7.0) phosphate buffer. An antioxidant assay of shinorine showed its efficient activity as antioxidant which increased in a dose-dependent manner. � 2021, King Abdulaziz City for Science and Technology.
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    Ultraviolet radiation and salinity-induced physiological changes and scytonemin induction in cyanobacteria isolated from diverse habitats
    (AMG Transcend Association, 2022) Pathak, Jainendra; Kumar, Deepak; Singh, Deepak K.; Ahmed, Haseen; Kannaujiya, Vinod K.; Sinha, Rajeshwar P.
    Enhanced ultraviolet radiation (UVR) in the atmosphere and increased salinity of soils and water adversely affect photoautotrophs' productivity. Several researchers have focussed on the use of non-arable or brackish environments for growing strains suitable for the production of value-added products along with biofuels. In this regard, cyanobacteria serve as good model organisms as they can survive and sustain themselves in habitats characterized by high UV influx and changing salinities. Thus, these photoautotrophs can help understand the complex physiological processes and adaptations occurring in higher plants growing in stressed environments of salinity and UVR. In the present investigation, cumulative effects of salinity (NaCl: 50, 100, and 200 mM), photosynthetically active radiation (PAR), and UVR have been studied in terms of the reactive oxygen species (ROS) generation, total protein content, phycobiliproteins profile, and induction of scytoneminin in the two cyanobacteria isolated from different habitats. Production of ROS increased after PAR+UV-A+UV-B, PAR+UV-A, and PAR exposure, and maximum generation occurred in the samples treated with 200 mM NaCl. Total protein content and phycobiliproteins profile was severely affected by these stresses. The maximum induction of scytonemin occurred in the cultures with 200 mM of NaCl and PAR+UV-A+UV-B exposure for 72 h. Our results indicate that Scytonema sp. could serve as a potential candidate for bioremediation of saline soils along with the production of value-added metabolite scytonemin. � 2021 by the authors.
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    UV-induced physiological changes and biochemical characterization of mycosporine-like amino acid in a rice-field cyanobacterium Fischerella sp. strain HKAR-13
    (Elsevier B.V., 2022) Singh, Vidya; Pathak, Jainendra; Pandey, Abha; Ahmed, Haseen; Rajneesh; Kumar, Deepak; Sinha, Rajeshwar P.
    Mycosporine-like amino acids (MAAs) are valuable secondary metabolite with notable photoprotective potential. The present study investigateS the im???ts of ?h?t?syntheti? ??tive r?di?ti?n (??R) and ultraviolet radiation (UVR) on various physiological processes in the cyanobacterium Fischerella sp. strain HKAR-13. Cell viability was reduced by 36 and 65% after 72h of ex??sure to ??R+UV-? (PA) and ??R+UV-?+UV-B (PAB) radiations respectively. Significant decline in Chl a content was observed during PA and PAB exposure after 36h. Carotenoid content increased significantly after 48h of exposure, thereafter began to decline. Cultures exposed to PAB showed maximum detrimental effect on protein synthesis. In PAB and PA, the levels of intracellular reactive oxygen species (ROS) increased significantly. Fluorescence microscopic images of cyanobacteria revealed generation of ROS in UVR as indicated by increase in green fluorescence. Besides, Fischerella sp. strain HKAR-13 was also tested for the ?resen?e of M??s and their induction under UVR. UV-Vis spectrophotometry and high-?erf?rm?n?e liquid ?hr?m?t?gr??hy ?n?lyses revealed the ?resen?e of a MAA having absorption maxima ?max 334 nm and retention time of 1.5 min. Maximum induction of MAA was found in samples exposed to PAB followed by PA. Based on electrospray ionization-mass s?e?tr?s???y (m/z: 333+1), fourier transform infrared and nuclear magnetic res?n?n?e s?e?tr?s???y, the MAA was identified as shinorine. Shinorine was found to be highly stable under some abiotic stress factors such as UV-B, temperature and H2O2. It also showed efficient antioxidant activity in a dose-dependent manner as depicted by in vitro antioxidant assays. � 2022 SAAB