Environmental Engineering Reference
In-Depth Information
production as well as lessening in the efficiency of ROS scavenging may equally disturb
this balance and lead to oxidative stress conditions. It is important to emphasise that -
not only in plants, but - in any biological system, the magnitude of detectable oxidative
damage depends on both ROS production and disproportioning.
Plants are well equipped with both enzymatic and non-enzymatic antioxidants
(Fig.3). A central element of the system is ascorbate (vitamin C), acting both directly
and as a cofactor of the ascorbate peroxidase enzyme. Ascorbate and glutathione are
free radicals scavenger, but are also important regenerating other antioxidants, for
instance tocopherol, from their radical form. Carotenoid pigment also play an important
role in defence, mainly against damage by singlet oxygen. The backbone of the
enzymatic defence is the tandem functioning of superoxide dismutase and ascorbate
peroxidase, together with other enzymes involved in the synthesis and recycling of
ascorbate (for reviews see Refs. 13,14). Other peroxidases, such as catalase, glutathione
peroxidase and guiacol peroxidase are also involved, although their role is limited to
certain cell compartments.
Fig. 3. Schematic pathways of disproportioning ROS in plants. Enzymes are underlined, non-enzymatic
antioxidants are in italics. APX: ascorbate peroxidase, AsA: ascorbate, Car: E-carotin, GSH, reduced
glutathione, MDAR: monodehydro-ascorbate reductase, POD: peroxidase including catalase, SOD:
superoxide dismutase, Toc: D-tocopherol
3. The oxidative nature of UV-B (280-320 nm) stress
Changes in the biotic environment, such as increasing solar UV irradiation-or
the appearance of abiotic stress factors may result in the oxidative damage of structures
(membrane lipid, protein) or functions (redox component, enzyme) causing smaller
bioproduction and - under extreme conditions - even the irreversible damage.
Regarding its central role in the damaging process and potential involvement as
activator of the defence system, ROS detection is of special importance.
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