Ultraviolet radiation reduces plant leaf area, inhibits hypocotyl elongation, reduces photosynthesis and productivity, and makes plants susceptible to pathogen attack, but can induce flavonoid synthesis and defense mechanisms. UV-B can reduce the content of ascorbic acid and β-carotene, but can effectively promote anthocyanin synthesis. UV-B radiation results in a dwarf plant phenotype, small, thick leaves, short petiole, increased axillary branches, and root/crown ratio changes.
The results of investigations on 16 rice cultivars from 7 different regions of China, India, the Philippines, Nepal, Thailand, Vietnam and Sri Lanka in the greenhouse showed that the addition of UV-B resulted in an increase in the total biomass. Cultivars (only one of which reached a significant level, from Sri Lanka), 12 cultivars (of which 6 were significant), and those with UV-B sensitivity were significantly reduced in leaf area and tiller size. There are 6 cultivars with increased chlorophyll content (2 of which reach significant levels); 5 cultivars with significantly reduced leaf photosynthetic rate, and 1 cultivar with significantly improved (the total biomass is also significant) increase).
The ratio of UV-B/PAR is an important determinant of plant response to UV-B. For example, UV-B and PAR together affect the morphology and oil yield of mint, which requires high levels of unfiltered natural light.
It should be noted that laboratory studies of UV-B effects, although useful in identifying transcription factors and other molecular, physiological factors, are due to the use of higher UV-B levels, no UV-A concomitant and Often low background PAR, the results are usually not mechanically extrapolated into the natural environment. Field studies typically use UV lamps to raise or use filters to reduce UV-B levels.