oxidants and antioxidants in biology - Oxygen Club of California

Oxidative stress, antioxidants, and plant mitochondria
C. H. FOYER 1 , R. DE PAEPE 2 AND G. NOCTOR 2
1 Crop Performance and Improvement Division, Rothamstead Research,
Harpenden, UK; 2 Institut de Biotechnologie des Plantes, Bâtiment 630, Université
Paris XI, 91405 Orsay cedex, France
Mitochondria have not traditionally been regarded as a major
source of active oxygen species in leaves. As a result of photosynthesis,
up to 100 µmol H 2 O 2 per mg chlorophyll is produced in the
peroxisomes of a C 3 leaf and up to about 30 µmol H 2 O 2 in the chloroplasts.
In contrast, the maximum rate of H 2 O 2 formation due to
the mitochondrial electron transport chain is likely to be much less
than 1 µmol under the same conditions. Nevertheless, the mitochondrial
oxidative load could be crucial in influencing and setting
the cellular redox-state. Plants have a robust tolerance of high rates
of H 2 O 2 formation because of the action of the antioxidative system.
Mitochondria, like other compartments of the plant cell, house
both enzymic and non-enzymic antioxidants. The last step of
ascorbate biosynthesis is located in the inner mitochondrial menbrane,
where it is coupled to electron flow. Ascorbate liberated into
the intermembrane space is translocated to the rest of the cell.
Moreover, mitochondria contain specific soluble and bound forms
of ascorbate peroxidase (APX), both in the matrix and the intermembrane
space. The distribution of APX between these two mitochondrial
compartments appears to be crucial in determining stress
resistance. Changes in the redox state of the mitochondrial electron
transport chain initiate signalling that resets the antoxidative capacity
throughout the cell.
[Supported by Alliance Franco-British Partnership (Project PN 01.015)]
64