The Anabaena sp. PCC 7120 is a filamentous cyanobacterium which is well known for its nitrogen fixing ability but nickel (Ni2+) contamination (in water bodies) has a negative impact on its growth. The negative impact of Ni2+ can be ameliorated by calcium (Ca2+)-mediated nitric oxide (NO) signaling induced by salicylic acid (SA) treatment. The present study was performed to investigate the relation between SA and NO mediated by Ca2+ and to understand this interaction several inhibitors and scavengers were used in different combinations. Results showed that Ni2+- toxicity declined growth (measured in terms of dry weight; DW), contents of exopolysaccharide and photosynthetic pigments, and also negatively affected the PSII photochemistry (OJIP transient parameters: F-m, F-v, F-m/F-o,F- F-v/F-o, Psi(o), Phi P-o, Phi E-o, Area, N, and PIABS were suppressed; while F-o, F-o/F-m, F-o/F-v, S-m, Phi D-o, ABS/RC, TRo/RC, ETo/RC and DIo/RC were raised) and nitrogen metabolism. However, supplementation of SA, Ca2+ (CaCl2) and sodium nitroprusside (SNP; donor of nitric oxide (NO) to the culture medium counteracted the negative impact of Ni2+ thereby improving the growth. Further, to investigate the relation between Ca2+ and NO, when c-PTIO (2-4-carboxyphenyl- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; scavenger of NO) was supplemented to Ni+SA+Ca2+ and EGTA (ethyleneglycol-bis (beta- aminoethyl)- N,N,N,N- tetraacetic acid; Ca2+ chelator) to Ni+SA+NO treated culture medium, the recovery on above studied traits caused due to Ca2+ and NO was arrested even in presence of SA suggesting the signaling behavior of Ca2+ and NO in SA induced pathway. Moreover, the impact was worsened under c-PTIO supplemented Ni+SA+Ca2+ than EGTA supplemented Ni+SA+NO treatment suggesting key role of Ca2+ in mediating NO signaling induced by SA. Conclusively, this is the first study that demonstrates the relation between SA and NO mediated by Ca2+ in Ni2+-stressed Anabaena sp. PCC 7120. (c) 2022 SAAB. Published by Elsevier B.V. All rights reserved.
