The deteriorative effect of ultraviolet-B (UV-B) radiation on photosynthesis was assessed by the simultaneous measurement of O2 evolution and chlorophyll (Chl) fluorescence in green pepper.
UV-B was given at the intensity of 1 W·m-2, a dosage often encountered in urban area of Seoul in Korea, to the detached leaves.
Both Pmax and quantum yield of O2 evolution was rapidly decreased, in a parallel phase, with increasing time of UV-B treatment.
Chl fluorescence parameters were also significantly affected.
Fo was increased while both Fm and Fv were decreased.
Photochemical efficiency of PS II (Fv / Fm) was also declined, although to a lesser extent than Pmax.
Both qP and NPQ were decreased similarly with increasing time of UV-B treatment.
However, PS I remained stable.
The addition of lincomycin prior to UV-B treatment accelerated the decline in Fv / Fm to some extent, suggesting that D1 protein turnover may play a role in overcoming the harmful effect of UV-B.
The amount of photosynthetic pigments was less affected than photosynthetic response in showing decline in Chl a and carotenoids after 24 h-treatment.
Presumptive flavonoid contents, measured by changes in absorbance at 270 nm, 300 nm and 330 nm, were all increased by roughly 50% after 8 h-treatment.
Among antioxidant enzymes, activities of catalase and peroxidase were steadily increased until 12 h of UV-B treatment whereas ascorbate peroxidase, dehydroascorbate reductase and glutathione reductase did not show any significant change.
The results indicate that deteriorative effect of UV-B on photosynthesis precedes the protection exerted by pigment synthesis and antioxidant enzymes.