Leaf epidermal transmittance of ultraviolet radiation and its implications for plant sensitivity to ulraviolet-radiation induced injury

Abstract

Leaf epidermal transmittance of ultraviolet radiation (280–400 nm) was examined in several plant species to determine the capability of the epidermis to attenuate solar ultraviolet radiation. Epidermal samples were mechanically isolated and examined with a spectroradiometer/integrating sphere for transmittance. A survey of 25 species exposed to natural insolation was conducted. Although the species differed in life form, habitat type, and epidermal characteristics, epidermal transmittance was generally less than 10%. Ultraviolet radiation was attenuated 95 to 99% in more than half of the species. In 16 species, flavonoid and related pigments in the epidermis accounted for 20 to 57% of the attenuation. Several species exposed to supplemental ultraviolet irradiation (288–315 nm) in a greenhouse exhibited significant (P≦0.05) depressions in epidermal transmittance of 31 to 47%, apparently resulting from an increase in ultraviolet-absorbing pigments.