Chemical composition of tobacco leaves altered by near-ultraviolet and intensity of visible light.

Low energies of near-ultraviolet radiation (300-400 nanometers), applied simultaneously with visible radiation to Nicotiana tabacum L. during daily illumination periods, increased levels of chlorogenic acid isomers, total soluble phenolics, alkaloids, and soluble sugars in expanding leaf lamina compared with controls that had near-ultraviolet filtered out. However, total nitrogen concentrations decreased. The responses to near-ultraviolet were interrelated with intensity of visible light. The presence of near-ultraviolet (which accounted for less than 4% of the total light energy) along with visible light resulted in component concentration differences similar to those caused by much greater increases of visible light without near-ultraviolet.