Untitled

Abstract

Leaves of Vicia faba were collected from the field and the greenhouse and transmittance of epidermal peels from adaxial and abaxial sides was determined in the wavelength range from 250 to 800 nm using a spectrophotometer equipped for the measurement of turbid samples. From the same leaves, epidermal 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. Transmittances 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 abaxial 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 methanolic 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 fluorescence method which allows rapid measurements on intact leaves can provide a quantitative estimate of epidermal transmittance for UV-B (280-320 nm) and UV-A (320-400 nm) radiation.

UV screening by phenolics in berries of grapevine (Vitis vinifera)

“…Increasing flavonoid levels in the leaf, however, do not necessarily correspond with improved epidermal UV screening because considerable fractions of flavonoids are located in the mesophyll in some plant species (Burchard et al 2000;Rozema et al 2002;Semerdjieva et al 2003). Studies combining flavonoid quantification with measurements of epidermal transmission for UV radiation, however, have indicated that flavonoid levels increased by UV radiation result in improved UV screening (Burchard et al 2000;Mazza et al 2000;Bilger et al 2001;Kolb et al 2001;Markstädter et al 2001;Krause et al 2003). This is consistent with the view that natural UV-B intensities reduce epidermal UV transmittance by stimulating synthesis of epidermal flavonoids.…”

“…Kolb et al 2001). The degree to which hydroxycinnamic acids support flavonoid screening, however, differs markedly between species; they contribute minimally to UV-B screening in leaves of Vicia faba (Markstädter et al 2001), but considerably in Arabidopsis thaliana and grapevine (Landry et al 1995;Sheahan 1996;Kolb et al 2001). Further, in primary leaves of rye (Secale cereale), the importance of hydroxycinnamic acids for UV screening depends on the developmental stage (Burchard et al 2000).…”

Do mature shade leaves of tropical tree seedlings acclimate to high sunlight and UV radiation?

“…In an earlier study (Krause et al 1999a), a small increase in UV-absorbing compounds obtained by 0.5 h d~ ' sun exposure of shade-grown plants of Virola surinamensis resulted in effective protection of PSII against solar UV-B. Probably relatively small amounts of protective substances suffice when they are accumulated in the adaxial leaf epidermis (Markstädter et al 2001). As recently reported by Liakoura et al (2003), shade leaves of Mediterranean woody plants were perfectly protected against UV-B by their epidermis, although leaf extracts exhibited much lower UV absorbance than those obtained from sun leaves.…”

A new optical leaf‐clip meter for simultaneous non‐destructive assessment of leaf chlorophyll and epidermal flavonoids

“…Ideally it should be a leaf without epidermis with an equal excitation of Chl fluorescence at 650 nm (red) and 375 nm (UV-A) (Barnes et al 2000). Markstädter et al (2001) propose to divide the measurements on the sample by the identical measurement (same device, same conditions) of peeled leaves or, if leaf peeling is not possible, a blue foil standard that has fluorescence properties similar to that of leaves (Kolb et al 2001, Markstädter et al 2001). The standard blue fluorescent foil used by FORCE-A has different spectral characteristics than Chl in vivo.…”