............and on the way found this
Responses in surface structure and chemistry
Outdoor UV-B supplementation studies of higher plants involving modulated lamp banks have revealed some significant responses, but plant responses to UV-B generally seem to be more subtle than those based on exclusion studies. The most consistent response in higher plants was an increase in the concentrations of soluble leaf UV-B-absorbing compounds. Phenylpropanoids, e.g. hydroxycinnamic acid, cinnamoyl esters, and flavonoids, including flavones and flavonols, and anthocyanins provide a UV-A and UV-B screen in higher plants. The flavonoids responsible for UV screening vary from species to species, and most plants synthesize a range of compounds to provide more effective screening. So far, most of the studies have been made with summer-green species.
The studies with evergreens have shown that, in warm years, the production of soluble phenolics is higher compared to cold years. UV-B radiation and altitude alter the foliar flavonoid composition in forest tree species, such as Scots and ponderosa pine. The responses may be transient or long-lasting. Phenolics increase with needle age in Scots pine, black pine and ponderosa pine Enhanced UV-B radiation increased Scots pine needle cutinization and wall-bound phenolics as well as flavonoids, , which are important during the late winter and early spring.
The natural UV-screening mechanisms in evergreens have been shown to include UV light screening via reflectance of UV/violet light by the epidermis, UV light screening via reduction of transmission by special anatomical arrangement of epidermal cells as well as light-reflecting hyaline hypodermal cells, conversion of UV light via fluorescence and UV light screening by UV-screening substances in cell walls and on surfaces. In higher plants, anthocyanins and flavones increase in response to high visible light levels, and UV irradiation induces flavonoids, sinapate esters, isoflavonoids and psoralens, and in evergreens, diacylated flavonol monoglycoside induction, for example, has been detected and p-coumaric acid, ferulic acid and astragalins have been identified as UV-B-absorbing substances