255
caused by the oxidation of cluster leading to release of iron, which through Fenton
chemistry produces highly reactive OH
•
radicals (Kumar et al. 2011a, b). Protonation
of O 2
•− produces HO 2
• . At low pH, dismutation of O 2
•− is unavoidable, with one
O 2
•− giving up its added electron to another O 2
•− forming O 2
2− . Protonation of O 2
2−
results in the generation of H 2 O 2 . In the presence of transition metals like copper
and iron, further reactions through Haber-Weiss cycle or Fenton reaction forms
OH
•
, which is the most reactive chemical species in the biological world (Mittler
2002; Gill and Tuteja 2010).
Stress-induced ROS accumulation is counteracted by an integral defence mechanism of the cell, which, under normal conditions, scavenges the excess oxidants and
avoids the deleterious effects of ROS. This includes an array of enzymatic scavengers
such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX),
glutathione reductase (GR), etc. and non-enzymatic antioxidant molecules such as
pigments, proline, polysaccharides, polyphenols, carotenoids, flavonoids, etc. (Mittler
et al. 2004; Cirulis et al. 2013). Generation and scavenging of ROS and their effects on
cellular metabolites of microalgae are shown in Fig. 13.1. SOD is an important intracellular enzymatic antioxidant ubiquitous in all subcellular compartments of aerobic
organisms prone to ROS-mediated oxidative stress (Gill and Tuteja 2010). It provides
the first line of defence against toxic effects of ROS by catalysing dismutation of O 2
•−
Fig. 13.1 Generation and scavenging of ROS and their effects on cellular metabolites of
microalgae
13 Oxidative Stress-Induced Bioprospecting of Microalgae
caused by the oxidation of cluster leading to release of iron, which through Fenton
chemistry produces highly reactive OH
•
radicals (Kumar et al. 2011a, b). Protonation
of O 2
•− produces HO 2
• . At low pH, dismutation of O 2
•− is unavoidable, with one
O 2
•− giving up its added electron to another O 2
•− forming O 2
2− . Protonation of O 2
2−
results in the generation of H 2 O 2 . In the presence of transition metals like copper
and iron, further reactions through Haber-Weiss cycle or Fenton reaction forms
OH
•
, which is the most reactive chemical species in the biological world (Mittler
2002; Gill and Tuteja 2010).
Stress-induced ROS accumulation is counteracted by an integral defence mechanism of the cell, which, under normal conditions, scavenges the excess oxidants and
avoids the deleterious effects of ROS. This includes an array of enzymatic scavengers
such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX),
glutathione reductase (GR), etc. and non-enzymatic antioxidant molecules such as
pigments, proline, polysaccharides, polyphenols, carotenoids, flavonoids, etc. (Mittler
et al. 2004; Cirulis et al. 2013). Generation and scavenging of ROS and their effects on
cellular metabolites of microalgae are shown in Fig. 13.1. SOD is an important intracellular enzymatic antioxidant ubiquitous in all subcellular compartments of aerobic
organisms prone to ROS-mediated oxidative stress (Gill and Tuteja 2010). It provides
the first line of defence against toxic effects of ROS by catalysing dismutation of O 2
•−
Fig. 13.1 Generation and scavenging of ROS and their effects on cellular metabolites of
microalgae
13 Oxidative Stress-Induced Bioprospecting of Microalgae