Programmed cell death is induced by hydrogen peroxide but not by excessive ionic stress of sodium chloride in the unicellular green alga Chlamydomonas reinhardtii

Eukaryotic microalgae serve as indicators of environmental change when exposed to severe seasonal fluctuations. Several environmental stress conditions are known to produce reactive oxygen species in cellular compartments, resulting in oxidative damage and apoptosis. The study of cell death in higher plants and animals has revealed the existence of an active ‘programmed cell death’ (PCD) process and similarities between such processes suggest an evolutionary origin. A study was undertaken to examine the morphological, biochemical and molecular responses of the unicellular green alga Chlamydomonas reinhardtii after exposure to oxidative (10 mM H2O2) and osmotic (200 mM NaCl and 360 mM sorbitol) stress. Concentrations of H2O2 (2–50 mM), NaCl and sorbitol (100–800 mM) were negatively correlated with growth. Biochemical analyses showed an increase in intracellular H2O2 production (2.2-fold with H2O2 and ~1.2–1.4-fold with NaCl and sorbitol) and activities of some antioxidant enzymes [super oxide dismutase (SO...