Cucumber (Cucumis sativus L. cv. Dar) leaves exposed to UV-B irradiation at a biologically effective dose of 9.5 kJ m-2d-1 showed decreased chlorophyll fluorescence parameter values versus the control; in peppermint (Mentha piperita L. cv. Asia) leaves those values were almost unchanged after treatment. Fv/Fo and Rfd were reduced more than other values, indicating inhibition of the oxygen-evolving complex and cooperation between the light and dark photosynthesis reactions as the primary targets of UV-B. The photosynthetic electron transport rate showed less change directly after irradiation, but after 24 h of recovery it was reduced to 50% of the control. Generally, photosystem II of peppermint leaves appeared more tolerant to the applied UV-B radiation than in cucumber leaves.
Exposure of green algae Chlorella vulgaris to short-term UV-B radiation (280 nm – 315 nm) induced several changes in the function of photosystem II (PS II) studied by means of chlorophyll fluorescence (FL) and oxygen evolving. The intensity of photosynthetic oxygen evolving intensity of algae suspension decreased in a similar way to the FL parameter values in proportion to the applied dose of UV-B radiation (0.0, 3.2, 6.4, 12.8 kJ·m-2). The correlation between photosynthetic oxygen evolving intensity and FV/FO ratio was better than that between photosynthetic oxygen evolving intensity and FV/FM. The vitality index (Rfd) in the UV-B irradiated algae strongly decreased, compared to the control, which indicates inhibition of potential CO2 fixation and cooperation between light and dark reactions of photosynthesis. It may indicate damage of Rubisco.
The experiment on Zea mays L. cv. Landmark (F1) plants was performed in a greenhouse with UV-B (305–315 nm). The pots with plants were divided into four groups: the first and the second groups were grown, respectively, at low (1.0 kJ m-2 d-1) and high (3.0 kJ m-2 d-1) biological effective dose of UV-B radiation. Half of the pots of each group were sprayed with 0.1% solution of Asahi SL (the third and fourth groups). The intensity of photosynthesis and transpiration, chlorophyll fluorescence, the content of UV-absorbing compounds and radical scavenging activity were measured using DPPH after four and six weeks of UV-B radiation. After six weeks of irradiation with a higher UV-B dose both flavonoid content and antioxidant activity increased by 112% and by 44%, respectively, compared to the plants grown at the lower dose. The plants treated with Asahi SL and exposed to the high dose of UV-B had the content of flavonoids 80% higher than the control ones. Asahi SL decreased scavenging activity in both groups of plants by 17% and 32%, respectively, in comparison with the untreated plants. The intensity of net photosynthesis, the transpiration rate and chlorophyll fluorescence parameters (Fv/Fo, ETR, Rfd) did not differ in most of variants.