title: The alpha-tocopherol content of leaves of pedunculate oak (Quercus robur L.)--variation over the growing season and along the vertical light gradient in the canopy.
abstract: This study was performed in order to investigate whether the actual requirement for defence against photo-oxidative stress is reflected by the alpha-tocopherol (alpha-Toco) content in leaves of pedunculate oak (Quercus robur L.). Antioxidants and pigments were quantified in leaves that were collected on six days between May and September 2000 in a mixed pine/oak forest at canopy positions differing in light environment. Pools of hydrophilic antioxidants and photo-protective xanthophyll cycle pigments (V + A + Z) reflected the anti-oxidative demand, as these pools increased with the average light intensity to which the leaves were acclimated. The photo-protective demand was not the determinant of the alpha-Toco content of oak leaves, as (1) foliage of a young oak, exposed to low light levels in the understorey, contained higher amounts of this lipophilic antioxidant than leaves sampled from semimature oaks at canopy positions with a similar light environment, and (2) a strong increase in the alpha-Toco content over the growing season was detected at each investigated crown position, whereas the V + A + Z pool did not show a concomitant accumulation during leaf ageing. The rate of alpha-Toco accumulation differed distinctly between samples taken at different canopy positions.
authors.affiliation: Institut für Biologie, Pflanzenphysiologie, Humboldt-Universität zu Berlin, Unter den Linden 6, D 10099 Berlin, Germany. ute.hansen@rz.hu-berlin.de
authors.forename: Ute
authors.initials: U
authors.lastname: Hansen
authors.forename: Jenny
authors.initials: J
authors.lastname: Schneiderheinze
authors.forename: Simone
authors.initials: S
authors.lastname: Stadelmann
authors.forename: Barbara
authors.initials: B
authors.lastname: Rank
mesh_terms: D000064:Acclimatization; D000975:Antioxidants / Q000378:metabolism; D008027:Light; D018384:Oxidative Stress; D010860:Pigments, Biological / Q000378:metabolism; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects; D029963:Quercus / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D012621:Seasons; D024341:Xanthophylls / Q000378:metabolism; D024502:alpha-Tocopherol / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D010860:Pigments, Biological; D024341:Xanthophylls; D024502:alpha-Tocopherol