The effects of UV‐B radiation on epidermal anatomy in loblolly pine (Pinus taeda L.) and Scots pine (Pinus sylvestris L.)

Abstract

The effects of enhanced UV‐B radiation on the needle anatomy of loblolly pine (Pinus taeda L.) and Scots pine (Pinus sylvestris L.) were studied in the field under supplemental UV‐B radiation supplied by a modulated irradiation system. The supplemental UV‐B levels were designed to simulate either a 16 or 25% loss of stratospheric ozone over College Park, Maryland. Enhanced UV‐B radiation caused different responses in these two species. The needles of loblolly pine had larger amounts of tannin in the lumen of epidermal cells and more wall‐bound phenolics in the outer epidermal walls of UV‐B‐treated needles, whereas the most pronounced effect on Scots pine needles was increased cutinization. In both species, the outer epidermal cell walls thickened and the needle cross‐sectional and mesophyll areas decreased (statistically significantly only in Scots pine). This suggests that more carbon may have been allocated to the protection mechanisms at the expense of photosynthetic area. The difference in response between these species suggests that the response to UV‐B radiation is not mediated by a single mechanism and that no generalization with regard to the effects of UV‐B on conifers can be made.

Does the azimuth orientation of Norway spruce (Picea abies/L./Karst.) branches within sunlit crown part influence the heterogeneity of biochemical, structural and spectral characteristics of needles?

“…Moreover, phenolic compounds accumulate in needles during high UV-B irradiance conditions since they are involved in UV-B protection (Laakso et al, 2000). Indistinguishable differences in amounts of phenolic compounds detected in needles of different azimuthoriented branches suggest identical levels of stress in all of four azimuth directions.…”

Efeitos da radiação ultravioleta-B sobre a morfologia foliar de Arabidopsis thaliana (L.) Heynh. (Brassicaceae)

“…Para algumas espécies, a penetração da radiação na lâmina foliar é atenuada pelas camadas epicuticulares e pela cutícula (Laakso et al 2000) assim como pela presença de hipoderme (Day et al 1992;Day 1993).…”

“…No entanto, concentrações significativas podem ocorrer no mesofilo de algumas espécies (Day 1993). Independente da região foliar nas quais estes compostos ocorrem, a radiação UV-B parece induzir a produção de compostos fenólicos nas folhas de várias espécies vegetais (Day 1993;Hoque & Remus 1999;Laakso et al 2000), como um mecanismo fotoprotetor. Neste estudo, as maiores concentrações de compostos fenólicos nas folhas tratadas com UV-B também podem ser resultante da maior espessura da lâmina, uma vez que os valores médios destes compostos foram calculados por unidade de área.…”

UV-B Inhibits Leaf Growth through Changes in Growth Regulating Factors and Gibberellin Levels

“…Existing data on the effects of UV-B on cell proliferation and cell expansion are contradictory, probably reflecting differences in experimental conditions. Acute, stress-inducing UV-B conditions usually inhibit cell proliferation, while both cell proliferation and expansion are affected by lower doses and/or chronic UV-B treatments (Staxen and Bornman, 1994;Nogués et al, 1998;Laakso et al, 2000;Hopkins et al, 2002;Hofmann et al, 2003;Kakani et al, 2003;Hectors et al, 2007Hectors et al, , 2010Wargent et al, 2009;Robson and Aphalo, 2012). For example, the number of epidermal cells at maturity decreased after UV-B exposure in some species (Gonzalez et al, 1998;Hopkins et al, 2002); on the contrary, in lettuce (Lactuca sativa) leaves, UV-B reduced cell expansion rate and final leaf size (Wargent et al, 2009).…”