Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

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A.R. Reddy and A.S. Raghavendra
The ROS are also produced in different cellular components including chloroplasts,
mitochondria, peroxisomes, glyoxysomes, cell wall, plasma membrane and
apoplasts (Figure 2). However, as depicted in Figure 2, the chloroplasts, mitochondria
and the microbodies are the main sources of ROS in the plant cell.
Figure 2. Generation of reactive oxygen species in different cellular compartments
Although chloroplast was considered to be the main source of ROS production,
recent studies suggest some intriguing possibilities about other cellular organelles
as additional sources of ROS generation. Plant hypersensitive response and programmed
cell death were partly attributed to the enhanced levels of ROS in mitochondria
(Lam et al., 2001). In plant cells, mitochondrial ETC is a major site of ROS production
(Moller, 2001; Tiwari et al., 2002). In addition to the complexes I-IV, the plant mitochondrial
ETC contains proton pumping alternative oxidases as well as two non-proton
pumping NAD(P)H dehydrogenases on each side of the inner membrane. Complex I is
the main enzyme oxidizing NADH under normal conditions and is also a major site of
ROS generation (Figure 2). Several antioxidant enzymes are also reported in the matrix
along with some antioxidants like glutathione to remove ROS produced under conditions
of oxidative stress (Purvis, 1997; Braidot et al., 1999;). The entire ascorbate-glutathione
cycle has been reported to occur in pea leaf mitochondria (Jimehez et al., 1998).