Effects of Natural Intensities of Visible and Ultraviolet Radiation on Epidermal Ultraviolet Screening and Photosynthesis in Grape Leaves

Abstract

Grape (Vitis vinifera cv Silvaner) vine plants were cultivated under shaded conditions in the absence of ultraviolet (UV) radiation in a greenhouse, and subsequently placed outdoors under three different light regimes for 7 d. Different light regimes were produced by filters transmitting natural radiation, or screening out the UV-B (280-315 nm), or screening out the UV-A (315-400 nm) and the UV-B spectral range. During exposure, synthesis of UV-screening phenolics in leaves was quantified using HPLC: All treatments increased concentrations of hydroxycinnamic acids but the rise was highest, reaching 230% of the initial value, when UV radiation was absent. In contrast, UV-B radiation specifically increased flavonoid concentrations resulting in more than a 10-fold increase. Transmittance in the UV of all extracted phenolics was lower than epidermal UV transmittance determined fluorimetrically, and the two parameters were curvilinearly related. It is suggested that curvilinearity results from different absorption properties of the homogeneously dissolved phenolics in extracts and of the non-homogeneous distribution of phenolics in the epidermis. UV-B-dependent inhibition of maximum photochemical yield of photosystem II (PSII), measured as variable fluorescence of dark-adapted leaves, recovered in parallel to the buildup of epidermal screening for UV-B radiation, suggesting that PSII is protected against UV-B damage by epidermal screening. However, UV-B inhibition of CO 2 assimilation rates was not diminished by efficient UV-B screening. We propose that protection of UV-B inactivation of PSII is observed because preceding damage is efficiently repaired while those factors determining UV-B inhibition of CO 2 assimilation recover more slowly.Photosynthetic organisms form energy-rich compounds using the energy of the sun's visible radiation. When harvesting light, photosynthetic organs are inevitably exposed to the UV region of natural radiation. In general, UV radiation damages lipids, nucleic acids, and proteins in leaves of higher plants, and specifically targets the photosystem II (PSII) reaction center, Rubisco, chloroplast ATPase, and violaxanthin deepoxidase (Jordan, 1996;Vass, 1997).To cope with UV radiation damage, plants have evolved a variety of mechanisms including: screening out UV radiation by accumulating UV-absorbing phenolic compounds in the leaf epidermis, repairing UV-induced DNA damage, and formation of antioxidants to scavenge peroxides and oxygen radicals (Bornman and Teramura, 1993; Jordan 1996). Increases in natural UV radiation due to decreased stratospheric ozone concentrations have stimulated research on mechanisms and maximum capacities for protection against UV exposure (Caldwell et al., 1998).Studies with Arabidopsis mutants deficient in synthesis of phenolic sunscreens have demonstrated the essential role of epidermal screening in UV protection (Li et al., 1993; Lois and Buchanan, 1994; Landry et al., 1995; Booij-James et al., 2000; Mazza et al., 2000). In many higher plants, two classes...

Photoprotection, photosynthesis and growth of tropical tree seedlings under near-ambient and strongly reduced solar ultraviolet-B radiation

“…In leaves of C. longifolium, PSII 'recovered' faster than >4 max (Fig. 4b), similar to recovery responses of C0 2 assimilation and F v /F m in leaves of grapevine (Vitis vinifera L.) that were exposed to full sunlight following growth in the greenhouse under low UV irradiance and PAR (Kolb et al, 2001). Decreased F v /F m ratios recorded at the adaxial leaf side indicate photoinhibition occurring predominantly in the upper chloroplast layers (Lichtenthaler et al, 2005), which might be partly responsible for the differences between the response of F w IF m and A max .…”

“…Nevertheless, it is clear that terrestrial plants have a broad capacity to tolerate relatively high levels of UV-B light (Allen et al, 1998). UV-absorbing compounds such as flavonoids and hydroxycinnamic acids are thought to be essential for UV protection (Burchard et al, 2000;Caldwell et al, 1983;Cockell and Knowland, 1999;Kolb et at., 2001;Mazza et al, 2000;Reuber et al, 1993). They act most effectively when accumulated in the upper (adaxial) leaf epidermis (Flint et al, 1985;Markstadter et al, 2001).…”

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

“…Moreover, increases in xanthophyll-cycle pool size, midday deepoxidation levels and photosynthetic capacity were observed in leaves of shade-grown tree seedlings of four dipterocarp species (from the south-east Asian rain forest) exposed to full solar irradiance (Bungard et al 2000). The high initial susceptibility of PSII to photoinhibition in shade leaves was reduced upon high-light treatments (Mulkey and Pearcy 1992;Lovelock et al 1994;Bungard et al 2000;Kolb et al 2001). Changes in chloroplast structure and levels of chloroplast proteins were found upon high-light acclimation of mature leaves of the tropical epiphytic species, Guzmania monostachia (L.) Rusby ex Mez (MaxweUeia/.…”

Assessment of impact of solar UV components on growth and antioxidant enzyme activity in cotton plant

“…Exclusion of solar UV reduced the synthesis of UV absorbing substances in the leaves (Table 3). Flavonoids and other phenolic compounds which are the products of secondary metabolism act as UAS and filter the ambient solar UV (Kolb et al 2001). When the plants are grown after excluding UV, there is a signal transduction that alters the metabolism and reduces the synthesis of UAS and total phenolics content (Table 3).…”