Plant photosynthesis results in the production of
molecular oxygen. An inevitable consequence of this normal
process is the production of reactive oxygen species
(ROS) by the transfer of electrons to molecular oxygen.
Plants are adequately protected by the presence of multiple
antioxidative enzymes in different organelles of the
plant such as chloroplasts, cytosol, mitochondria and peroxisomes.
Under high light and CO2 limiting conditions
caused by environmental stress like salinity, these antioxidative
enzymes play an important role in scavenging
toxic radicals. To investigate the functions of antioxidative
enzymes in a mangrove plant, we isolated three
cDNAs encoding cytosolic Cu–Zn SOD (Sod1), catalase
(Cat1) and ferritin (Fer1) from Avicennia marina cDNA
library. Sod1, Cat1 and Fer1 cDNA encoded full-length
proteins with 152, 492 and 261 amino acids respectively.
We studied the expression of these antioxidant genes in
response to salt, iron, hydrogen peroxide, mannitol and
light stress by mRNA expression analysis. Cat1, Fer1
showed short-term induction while Sod1 transcript was
found to be unaltered in response to NaCl stress. A decrease
in mRNA levels was observed for Sod1, Cat1 while
Fer1 mRNA levels remained unaltered with osmotic stress
treatment. Sod1, Cat1 and Fer1 mRNA levels were induced
by iron, light stress and by direct H2O2 stress
treatment, thus confirming their role in oxidative stress
response.