Differential response of antioxidant compounds to salinity stress in salt-tolerant and salt-sensitive seedlings of foxtail millet (Setaria italica)

The modulation of antioxidant components was comparatively analysed in a salt-tolerant (cv. Prasad) and salt-sensitive (cv. Lepakshi) cultivar of foxtail millet (Setaria italica L.) under different NaCl concentrations. Under conditions of salt stress, the salt-tolerant cultivar exhibited increased total superoxide dismutase (SOI) and ascorbate peroxidase (APX) activity whereas both enzyme activities decreased in acutely salt stressed seedlings of the sensitive cultivar. At 200 mM NaCl, the tolerant foxtail millet cultivar responded with induction of cytosolic Cu/Zn-SOD and the Mn-SOD isoform at the protein level, The induced accumulation of the cytosolic Cu/Zn-SOD protein/activity is positively correlated with an elevated level of the cytosolic APX gene activity. The elevated cytosolic Cu/Zn-SOD and cytosolic APX activity correlates with an induced accumulation of their transcripts. Tolerant 5-day-old seedlings grown during high salinity treatment (200 mM NaCl) contained a lower amount of Na+ ions and showed a lower electrolyte leakage than sensitive seedlings. In conclusion, our comparative studies indicate that salt-induced oxidative tolerance is conferred by an enhanced compartment-specific activity of the antioxidant enzymes in response to compartment-specific signals.