Vol.:(0123456789) 1 3 Environmental Sustainability https://doi.org/10.1007/s42398-020-00146-6 ORIGINAL ARTICLE Response of a rice‑feld cyanobacterium Anabaena sp. HKAR‑7 upon exposure to ultraviolet‑B radiation and ammonium chloride Deepak Kumar Singh 1,2  · Jainendra Pathak 3  · Abha Pandey 1  · Vidya Singh 1  · Haseen Ahmed 1,4  · Deepak Kumar 1  · Rajneesh 1  · Rajeshwar Prasad Sinha 1 Received: 26 November 2019 / Revised: 30 August 2020 / Accepted: 3 November 2020 © Society for Environmental Sustainability 2020 Abstract Interactive efects of ultraviolet radiation (UVR), photosynthetically active radiation (PAR) and exogenously supplied ammo- nium chloride (NH 4 Cl) was studied in the rice-feld cyanobacterium Anabaena sp. HKAR-7. The cyanobacterium was cul- tured under varying NH 4 Cl concentrations i.e., 0, 50, 200, 500, 1000 and 5000 μM and 200 μM (concentration) was found to be optimum for the growth of the cyanobacterium. Detrimental efects of UV-B exposure were observed on photosynthetic pigments such as chlorophyll a (Chl a), carotenoids and phycocyanin (PC). However, damage to these pigments was less in the cyanobacterial samples supplemented with NH 4 Cl. Contents of Chl a and PC in cyanobacterial cells decreased upon UV-B exposure but decrement was less in the samples supplemented with NH 4 Cl. Upon UV-B exposure, carotenoids content enhanced initially (till 15 days) during the course of treatment (21 days) but signifcant decrease (in carotenoids content) was observed in later phase of the experiment. From the results of photosynthetic activity, maximum quantum efciency of PSII (Fv/Fm) and maximum electron transport rate (ETR max ), it could be concluded that exogenous supplementation of NH 4 Cl (optimum concentration) helped in protecting the cyanobacterial cells from highly energetic UVR to certain extent. Another interesting observation was signifcantly higher levels of biosynthesis and accumulation of mycosporine-like amino acids (MAAs) in the cyanobacterial cells supplemented with NH 4 Cl in comparison to non-supplemented cells. The purifed MAA was identifed to be phorphyra-334 as evidenced by UV/VIS absorption spectra, high performance liquid chromatography (HPLC) and electrospray ionization-mass spectrometry (ESI–MS). Keywords Ammonium chloride · Cyanobacteria Anabaena · Mycosporine-like amino acids · Photoprotection · Ultraviolet radiation Introduction Ultraviolet radiation (UVR), the comparatively low wave- band radiation, is composed of highly energetic photons which reach the Earth’s surface along with solar radiation. In current scenario, UVR infux has increased on the Earth due to anthropogenically released ozone depleting com- pounds (Häder et al. 2015). Although, UV-B constitute less than 1% of the total incoming solar radiation (Vincent and Roy 1993), it severely afects crucial biomolecules such as DNA, RNA and proteins which are important for biochemical, physiological and genetic functioning of the cell (Sinha and Häder 2016; Rajneesh et al. 2019). Besides, in cyanobacteria, detrimental efects of UVR on pigmentation, phycobiliprotein composition, motility, N 2 metabolism, DNA, protein profle and 14 CO 2 uptake have been well documented (Kannaujiya and Sinha 2015; Sinha Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42398-020-00146-6) contains supplementary material, which is available to authorized users. * Rajeshwar Prasad Sinha r.p.sinha@gmx.net; rpsinhabhu@gmail.com 1 Laboratory of Photobiology and Molecular Microbiology, Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi 221005, India 2 Department of Botany, Acharya Narendra Deo Kisan P. G. College, Gonda 271313, India 3 Department of Botany, Pt. Jawaharlal Nehru College, Banda 210001, India 4 Department of Botany, Government Girls PG College, Satna 485001, India