Homeostatic influence of calcium and kinetin: Regulation of defense strategies against NaCl stress in cyanobacterium Nostoc muscorum ATCC 27893

Abstract

• NaCl negatively affected the growth and growth related parameters i.e. proteins and exopolysaccharides contents, light harvesting pigments and photosynthesis as well as PS II photochemistry by increasing the oxidative stress. • Calcium and kinetin alleviated the toxicity induced by NaCl on cyanobacterial physiology. • Calcium is essentially needed for kinetin mediated regulation of NaCl toxicity. In the present study, the possible roles of kinetin (KN, 20 nM) and calcium (Ca 2+ , 0.8 mM) in the alleviation of the salinity stress (50 mM NaCl) induced damage on the growth, and metabolism of cyanobacterium Nostoc muscorum ATCC 27893 was explored. The results revealed that salinity stress decreased the growth, light-harvesting pigments (chlorophyll a , carotenoids and phycobiliproteins) and exopolysaccharides (EPS) contents, photosynthesis (whole-cell oxygen evolution), and the performance of PS II photochemistry [Chl a fluorescence kinetics: maximum photosynthetic quantum yield (Fv/Fm or Phi_Po), quantum yield of electron transport flux (Phi_Eo), yield of electron transport per trapped exciton (Psi_o), size and number of active photosynthetic reaction centers (Fv/Fo) and performance index (PI ABS )]. Reverse to this, enhancement of respiratory rate and values of PS II related energy flux parameters [absorption flux per reaction center (ABS/RC), trapping flux per reaction center (TRo/ RC), dissipation flux per reaction center (DIo/RC), and electron transport flux per reaction center (ETo/RC)], and rise in levels of oxidative biomarkers (superoxide radical; O 2 • , hydrogen peroxide; H 2 O 2, and malonaldehyde; MDA equivalents) even under accelerated activity of enzymatic antioxidants (superoxide dismutase; SOD, peroxidase; POD, catalase; CAT and glutathione-s-transferase; GST) were observed. Kinetin in presence of Ca 2+ improved the growth, pigments contents and performance of PS II photochemistry by down-regulating the oxidative stress biomarkres. Application of Ca 2+ scavenger (EGTA) in KN treated samples increased the damaging effect on growth and photosynthesis by aggravating oxidative stress under NaCl stress, thereby indicating the positive role of Ca 2+ in NaCl-induced toxicity alleviation by KN. The overall results suggest that Ca 2+ together with KN could be applied in paddy fields to up-regulate the growth of N 2 –fixing cyanobacterium Nostoc muscorum ATCC 27893, an inhabitant of paddy field under NaCl stress, hence they may be considered for sustainable agriculture.