2.2. Experimental design and treatments
The cultures of Anabaena PCC 7120 were harvested at their exponential phase by centrifugation at 4,000g for 10 min and gently washed thrice with distilled water. After this, cells were resuspended in BG-11 medium (pH 7.5) having different combinations of treatments viz., Ni (NiCl2; 1.5 μM), salicylic acid (SA; 40 μM), calcium (CaCl2; 800 μM), sodium nitroprusside (SNP; 10 μM), ethyleneglycol-bis (β- aminoethyl)- N,N,N,N- tetraacetic acid (EGTA; 1mM) and 2-4-carboxyphenyl- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO; 20 μM). The following combinations were made: control (only BG-11 medium), Ni, Ni+SA, Ni+Ca, Ni+NO, Ni+SA+Ca+c-PTIO, Ni+SA+NO+EGTA and Ni+SA+c-PTIO+EGTA. After 72 h of treatment, cultures were harvested and various parameters were analyzed.