Environmental Engineering Reference
In-Depth Information
DETECTING STRESS-INDUCED REACTIVE OXYGEN SPECIES IN PLANTS
UNDER UV STRESS
ÉVA HIDEG
Institute of Plant Biology, Biological Research Center
P.O.Box 521, Szeged, H-6701 Hungary
1. Abstract
Sunlight is the energy source for photosynthesis in all land plants and in many aquatic
organisms. On the other hand, solar irradiation may also appear as a stress, specially
when it is combined with other factors, such as deviations from optimal growth
conditions (temperature, water status) or with environmental pollutants (heavy metals,
air pollutants, acidic rain). The adaptation and acclimation of photosynthetic organisms
to changing environmental conditions is important, not only for the plant's survival but
also for manking utilising them as food, raw material and energy source. Reactive
oxygen species (ROS, also known as active oxygen species, AOS) are associated with
stress and stress response in many ways: They may appear as primary elicitors, as
propagators of oxidative damage, or as by-products. More recently, ROS are also
considered as messenger molecules involved in signalling pathways, thus potential
inducers of defence or adaptation. Until recently, the involvement of ROS in stress was
usually presumed from products of oxidative damage. These techniques are useful and
important, but
unlike more direct methods-they provide little information about the
primary reactions. Also, due to increasing recognition of ROS in signal transduction -
when they are present at low levels and do not cause much oxidative damage - methods
for direct ROS detection
in vivo
are of special importance. After giving an overview on
basic ROS chemistry, this chapter will illustrate direct and indirect methods of ROS
detection with special emphasis on plants and their response to UV-B (280-320 nm)
irradiation.
-
2. ROS and other free radicals in plants
2.1. PRODUCTION
ROS are produced from ground state (triplet,
3
O
2
) molecular oxygen, in two main
pathways. One is via energy transfer from an other triplet molecule forming singlet
oxygen (
1
O
2
), the other is via reduction (Fig. 1). The complete reduction of oxygen
yields water, the incompletely reduced intermediates are free radicals and a non-radical
form of ROS, H
2
O
2
(for reviews see Refs. 1,2) (Fig. 2). The production of hydroxyl
radicals is enhanced by the presence catalytic amounts of transition metals, specially
Fe(II) or Cu(I) in the so called Fenton reaction. Hydroxyl radicals may attack
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