The researchers studied how ultraviolet-B radiation affects photosynthesis in tobacco leaves. They found that exposure to UV-B led to a decrease in the maximum photosynthetic oxygen production and a decline in the efficiency of photosystem II. This decrease in efficiency was due to a reduction in the ability to dissipate excess energy, which ultimately inhibited photosystem II activity. UV-B treatment caused changes in chlorophyll fluorescence parameters, indicating a negative impact on the photosynthetic process.