Salicylic acid induced signaling against nickel-induced toxicity: Responses of growth, exopolysaccharides, phostosystem II photochemistry, nitrogen metabolism status and antioxidant system of Anabaena sp. PCC 7120

Abstract

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: Fm, Fv, Fm/Fo, Fv/Fo, Ψo, ФPo, ФEo, Area, N, and PIABS were suppressed; while Fo, Fo/Fm, Fo/Fv, Sm, ФDo, 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 (β- 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.