Epidermal flavonoids

WEI H, TYE L, BRESMiK E and BiRT D F (1990) Inhibitory effect of apigenin, a plant flavonoid, on epidermal ornilthine decarboxylase and skin tumor promotion in mice . Cancer Res, 50, 499-502. 

Figure 6. A Photomicrograph (x 51,000) of caffeine treated leaf epidermal cell showing electron-dense deposits on cell wall and membrane vesicles fusing with the plasmalemma (arrows). B Immunofluorescence labeling of flavonoids in cell walls of leaf epidermal strips (arrows) and autofluorescent stomata (x 62.5). C Immunogold labeling of the walls of a mesophyll cell (left, x 41,000). Ch, chloroplast EC, epidermal cell G, Golgi IS, intercellular space MC, mesophyll cell (right, control x 19,500).

Burchard, P., Bilger, W., and Weissenbock, G., Contribution of hydroxycinnamates and flavonoids to epidermal shielding of UV-A and UV-B radiation in developing rye primary leaves as assessed by ultraviolet-induced chlorophyll fluorescence measurements, Plant Cell Environ., 23, 1373, 2000. 

Schmelzer, E., Jahnen, W., and Hahlbrock, K., In situ localization of light-induced chalcone sythase mRNA, chalcone sythase, and flavonoid endproducts in epidermal cells of parsley leaves,... 

Almost every known member of the ABC family can be inhibited by one or more flavonoids [Brand et al., 2006], For example, in a human epidermal cell... 

Kim, H.P. Mani, L Iversen, L. Ziboh, V.A. 1998. Effects of naturally-occurring flavonoids and biflavonoids on epidermal cyclooxygenase and lipoxygenase from guinea-pigs. Prostag. Leukotr. Ess. Fatty Acids 58 17-24. 

Agarwal, R. et al.. Inhibitory effect of silymarin an antihepatotoxic flavonoids on TPA-induced epidermal ornithine decarboxylase activity and mRNA in SENCAR mice. Carcinogenesis, 15, 1099, 1994. 

Epidermal cells are on the upper and lower surfaces of a leaf. They have two features which prevent evaporative water loss they are packed densely together and they are covered by a cuticle, a waxy layer secreted by the cells. The epidennis usually consists of a single layer of cells, although the specialized leaves of some desert plants have epidermal layers which are several cells thick. Epidermal cells often have large vacuoles which contain flavonoid pigments. Elavonoids generally absorb ultraviolet radiation, and may act as a sort of natural sunscreen for the internal layers of the leaf, by filtering out harmful ultraviolet radiation from the sun. 

Brehem, B. G., Krell, D. 1975. Flavonoid localization in epidermal papillae of flower petals A specialized adaptation for ultraviolet absorption. Science 190 1221-1223. 

Kim, H. P. Pham, H. T. Ziboh, V. A., Flavonoids differentially inhibit guinea pig epidermal cytosohc phospholipase A2, Prostagl Leukotr. Essent. Fatty Acids, 2001, 65, 281-286. 

Anthocvanlns. Anthocyanlns are flavonoid, phenolic-based, water-soluble compounds located in the cell vacuole of the epidermal cells of many fruits and vegetables (371. They confer the characteristic red and blue colors of many flowers and fruits and as such are Important components of visual quality. The anthocyanins are pH indicators and are red at low pH, colorless at Intermediate pH and blue at higher pH. The blue colors at high pH are the result of copigmentation and metal chelation rather than a direct effect of pH. This can result in discoloration of fruits packed in metal containers or handled with metal implements (381. 

Anthocyanins, a class of flavonoids, are responsible for the red and purple colours associated with many fraits and vegetables. Anthocyanins occur in epidermal and subepidermal cells, dissolved in vacuoles or accumulated in vesicles called anthocyanoplasts. In general, the anthocyanin content in most fmits and vegetables varies between 0.1 and 1% of the diy matter content (Swain and Bate-Smith, 1962). 

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