P. Streb et al., LATENT OXIDATIVE STRESS RESPONSES OF OZONE-FUMIGATED CUCUMBER PLANTS ARE ENHANCED BY SIMULTANEOUS COLD EXPOSURES, Zeitschrift fur Naturforschung. C, A journal of biosciences, 51(5-6), 1996, pp. 355-362
Cucumber plants (Cucumis sativus L.) were grown under controlled condi
tions and fumigated with either O-3, diluted automobile exhaust or a c
ombination of both. The ratio of variable to maximum chlorophyll fluor
escence (F-v/F-m) was estimated as a measure of PSII activity. Activit
ies of the enzymes catalase, glutathione reductase and guaiacol-depend
ent peroxidase and contents of the antioxidants ascorbate and glutathi
one were assayed as potential indicators of oxidative stress. The beha
vior of catalase and of PSII are of particular diagnostic interest bec
ause they require continuous repair in light. Exposures of up to 13 da
ys to moderate concentrations of the pollutant gases alone did not ind
uce striking changes in any of the activities that were assayed. Also
when the plants were subjected to an additional stress treatment by ex
posing them to 4 short cold treatments (2h each at 0-4 degrees C in li
ght on days 12-15 after sowing) which induced marked declines of the F
-v/F-m ratio, the chlorophyll content and the catalase activity, these
cold-induced symptoms of photodamage were not significantly enhanced
by the fumigation treatments. However, increases of the activities of
glutathione reductase and peroxidase observed during a period of recov
ery following the cold-exposures were markedly higher in O-3-fumigated
plants, as compared to plants grown in filtered air or fumigated with
car exhaust alone. The results emphasize that effects of moderate pol
lutant exposures may be latent or delayed over long time periods and t
hat defence responses can be enhanced when plants are exposed to addit
ional, naturally occurring stress situations.