3.2. SA, Ca2+ and NO induces exopolysaccharides
(EPS) secretion to protect cells from Ni2+-induced
damage
The EPS secretion by cyanobacterial cells is a defense strategy to
combat from toxicity; which was found to decreased by 23% under
Ni2+-stress while upon SA, CaCl2 and
SNP addition, a sharp increment in EPS content was noticed with respect
to control (Fig.1B). The EPS synthesized by cyanobacteria either are
secreted in surrounding medium or attached with cell wall, which mainly
functions to protect the cell from environmental stresses like heavy
metals and pesticides (Tchounwou et al., 2012; Tiwari et al., 2020). Due
to its strong anionic nature (bearing sulphate groups and uronic acids),
it is suitable candidate in blocking the entry of toxic heavy metals
like cadmium (Jittawuttipoka et al., 2013). In addition, EPS also
provides microenvironment to maintain the level of essential elements,
which are in limited concentration in surroundings. Therefore, our
findings suggests that SA, Ca2+ and NO might have
induced the EPS level to restrict/ limit the Ni2+availability to the test organism as is also evident from biochemical
detection for intracellular Ni2+ accumulation (Fig.
1D). But this increment in EPS content was further arrested upon c-PTIO
and EGTA application thereby suggesting that in absence of
Ca2+ or/ and NO, SA was unable to protect the cell
from Ni2+-induced toxicity.