A three‐dimensional representation of the relationship between penetration of u.v.‐B radiation and u.v.‐screening pigments in leaves of Brassica napus

Abstract

SUMMARYA three-dimensional (3-D) representation of the penetration of u.v.-B (280-320 nm) radiation using fibre-optic microprobes, and of the spectrophotometric analysis of u.v.-screening pigments in leaves of Bras.ii.ca napus L. cv. Ceres is presented. In this way the results from radiation measurements were directly related to the distribution of u.v.-screening pigments. Brassica napus was grown in a greenhouse chamber with a photon flux density of 740 /imo\ m"^ s"^ photosynthetically active radiation (400-700 nm) with or without the addition of u.v.-B radiation. The amount of u.v-B added was equi\-alent to 9 kj m"' d"' biologically effective u.v.-B. Growth parameters measured included leaf thickness and dry weight. Ultraviolet-B radiation stimulated the accumulation of increased amounts of screening pigments, located mostly beneath the adaxial surface of tbe leaf, l^eaf dry weight decreased by 15 "o in u.v.-treated plants and, on a dry weight basis, chlorophyll content increased by 19 "o in treated leaves. The chlorophyll profiles within leaves from both control and u.v.-treated plants showed an increase from the adaxial surface to a plateau in the middle of the leaf, at a leaf depth of c. 150-320/im. Relatively large amounts of 285 nm radiation penetrated into leaves of u.v.-B treated plants to sites located within the initial 40 //m of the leaf. Thus, despite the presence of additional screening pigments, u.v.-B radiation was capable of reaching potential targets within the epidermis and mesophyll.

Response of wild-type and high pigment-1 tomato fruit to UV-B depletion: flavonoid profiling and gene expression

“…Using Wbre-optic microprobes, it was shown that UV-B radiation was capable to reach mesophyll in B. napus leaves and to enhance Xavonoids and phenolic compounds mostly in the epidermis, but also in the internal layers (Alenius et al 1995). Despite no data are presently available on the penetration of UV-B radiation in tomato fruits, our data indicate that most Xavonoid genes are aVected by UV-B depletion in the Xesh of both genotypes, suggesting that UV-B has a direct or indirect role in modulating gene expression in Xesh.…”

Plantas medicinais: fatores de influência no conteúdo de metabólitos secundários

“…Isso pode ser explicado, principalmente no caso de flavonóides e fenilpropanóides correlatos, pela proteção contra a foto-destruição proporcionada por estes metabólitos ao absorver e/ou dissipar a energia solar, dificultando assim a danificação dos tecidos mais internos pela radiação UV-B 101,[108][109][110] .…”

Potential Effects of UV-B on Photosynthesis and Photosynthetic Productivity of Higher Plants

“…Leaves contain water-soluble phenolic pigments, such as flavonoids, which strongly absorb UV-B radiation whilst not absorbing photosynthetically active radiation. These UV-B absorbing pigments are present throughout the leaf, but accumulate in adaxial epidermal cells [3][4] . UV-B radiation stimulates the expression of the genes encoding phenylalanine ammonia-lyase (PAL), the first stage of the phenylpropanoid pathway, and chalcone synthase (CHS), the key stage that commits the pathway to flavonoid synthesis (for reviews see Bornman and Teramura 5 , Beggs and Wellmann 6 , Jenkins et al 7 ).…”