Epidermal transmittance of leaves of Vicia faba for UV radiation as determined by two different methods

Leaves of Vicia faba were collected from the field and the greenhouse and t ransmittance of epidermal peels from adaxial and abaxial sides was determin ed in the wavelength range from 250 to 800 nm using a spectrophotometer equ ipped for the measurement of turbid samples, From the same leaves, epiderma l transmittance was estimated by a recently developed fluorometric method. Both methods gave highly correlated results with a slope of the regression line between both methods close to 1 and an intercept close to 0. Transmitt ances at around 310 nm as low as 3% were detected in the adaxial epidermis of field-grown leaves, while transmittance could be as high as 70% in the a baxial epidermis of greenhouse-grown leaves. There was a strong correlation between UV-A (ca. 366 nm) and UV-B (ca, 310 nm) transmittance detected by both methods which could be explained by the pigment composition in methano lic extracts where flavonols accounted for 90% of the absorption at 310 nm in the extract, while hydroxycinnamic acid derivatives which absorb only at the shorter wavelength constituted about 5%. It is concluded that the fluo rescence method which allows rapid measurements on intact leaves can provid e a quantitative estimate of epidermal transmittance for UV-B (280-320 nm) and UV-A (320-400 nm) radiation.