Interactive role of nitric oxide and 6-benzylaminopurine in enhancing antioxidant defense and improving salt stress tolerance in cyanobacterium Spirulina platensis

The present study examines the interaction of sodium nitroprusside (SNP) (nitric oxide donor) and 6- benzylaminopurine (6-BAP) in Spirulina platensis exposed to salt (NaCl) toxicity. Besides control, cultures treated with NaCl, NaCl+SNP, NaCl+6-BAP and NaCl+SNP+6-BAP were considered for investigating the interaction between SNP and 6-BAP. The results revealed that NaCl at 200 mM reduced photosynthetic pigment contents and photosynthesis (whole cell oxygen evolution and PS II photochemistry), thereby diminished the growth by 28% in Spirulina platensis . Salinity stress resulted in overproduction of oxidative stress biomarkers: superoxide radical (SOR; O 2 .− ), hydrogen peroxide (H 2 O 2 ) and malondialdehyde (MDA) contents. In spite of increased activity of antioxidant enzymes: superoxide dismutase (SOD), peroxidase (POD), and glutathione-S-transferase (GST) oxidative damage remained elevated. Cultures treated with NaCl+SNP, NaCl+6-BAP and NaCl+SNP+6-BAP combinations revealed reduced oxidative biomarkers, while significant rise in antioxidant enzyme activity was noticed as compare to respective values recorded in NaCl alone treated samples. The exogenous supplementation of SNP and 6-BAP alone and in combination (SNP + 6-BAP) significantly alleviated the decline in growth, photosynthetic pigment levels and also reduced the accumulation of oxidative biomarkers by boosting the enzymatic and non-enzymatic antioxidant system (superoxide dismutase, peroxidase, and glutathione-S-transferase activity). In brief, our findings reflect the possible interaction of NO and 6-BAP alone and in combination as a potential modulator of salt toxicity.