STUDENT ABSTRACTS - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 277

Effects of ultraviolet-b radiation and drought stress on Ocimum basilicum leaves
A. SZILÁGYI 1 , J.F. BORNMAN 1 , È HIDEG 2
1 Lund University, Lund, Sweden; 2 Biological Researcher Center, Szeged, Hungary
A reduction in stratospheric ozone results in a selective increase in the amount of
ultraviolet-B (UV-B, 280-315 nm) radiation reaching the earth's surface due to the
absorbing properties of ozone. Plants have evolved a range of mechanisms to protect
themselves against UV-B induced damage. One of them is an alteration of the
secondary metabolic pathways, including the enhancement of phenolic compounds such
as flavonoids. Certain of these chemical compounds have been shown to have
antioxidant properties.
Different light combinations have been tested in a nutritionally important plant
species, Ocimum basilicum , to maximise growth conditions for antioxidant-flavonoid
production. Plants were grown under visible light either alone or with an additional low
level of UV-B radiation. Three-week-old plants were exposed to oxidative stress by
applying (a) 13 kJ m -2 day -1 biologically effective (BE) UV-B for 8 days, (b) drought for
4 days and (c) drought and 13 kJ m -2 day -1 UV-B BE also for 4 days.
The photosynthetic activity of both control and UV-acclimated plants was
monitored during the stress experiments by measuring chlorophyll fluorescence
parameters of the leaves (F 0 , F m , F v /F m , yield, non-photochemical quenching). The effect
of UV-B radiation on the accumulation of total flavonoids was spectrophotometrically
measured during the stress treatments. Chemical assays were applied to detect the
formation of different reactive oxygen species (ROS). ROS production was also
estimated by measuring the EPR spectra. Results from plants exposed to UV-B are
shown in Figure 1. Acclimation to low levels of UV-B during growth enhanced the
ability of the plants to withstand a second, more severe stress by UV-B radiation. This
was reflected in smaller loss of photosynthetic yield and lower levels of lipid
peroxidation products and ROS in UV-acclimated plants than in non-acclimated
controls.

control + UV

control

UV-grown + UV

UV-grown

2 mT

2 mT

Figure 1. The EPR spectra show the amount of detected hydroxyl radicals in untreated (left panel)
and treated samples (right panel). The applied UV stress resulted in a higher amount of hydroxyl
radical production in the control basil leaves than in the UV-grown leaves.