Red : far-red light ratio and UV-B radiation: their effects on leaf phenolics and growth of silver birch seedlings

Authors

  • R. TEGELBERG,

    Corresponding author
    1. Natural Product Research Laboratories, University of Joensuu, Länsikatu 15, 80110 Joensuu, Finland,
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  • R. JULKUNEN-TIITTO,

    1. Natural Product Research Laboratories, University of Joensuu, Länsikatu 15, 80110 Joensuu, Finland,
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  • P. J. APHALO

    1. Faculty of Forestry, University of Joensuu, P.O.Box 111, 80101 Joensuu, Finland and
    2. Department of Biological and Environmental Science, University of Jyväskylä, P.O.Box 35, 40351 Jyväskylä, Finland
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Riitta Tegelberg. Fax: + 358 13 2513590; e-mail: Riitta.Tegelberg@joensuu.fi

ABSTRACT

The natural variation in quantity and quality of light modifies plant morphology, growth rate and concentration of biochemicals. The aim of two growth-room experiments was to study the combined effects of red (R) and far-red (FR) light and ultraviolet-B (UV-B) radiation on the concentrations of leaf phenolics and growth and morphology of silver birch (Betula pendula Roth) seedlings. Analysis by high-performance liquid chromatography showed that the leaves exposed to supplemental FR relative to R contained higher concentrations of total chlorogenic acids and a cinnamic acid derivative than the leaves treated with supplemental R relative to FR. In contrast, concentration of a flavonoid, quercetin 3-galactoside, was higher in the R + UV-B leaves than in the FR + UV-B leaves. The UV-B induced production of kaempferols, chlorogenic acids and most quercetins were not modified by the R : FR ratio. Growth measurements showed that the leaf petioles and stems of FR seedlings were clearly longer than those of R seedlings, but leaf area was reduced by UV-B radiation. Results of these experiments show that exposure of silver birch seedlings to supplemental FR compared to R leads to fast elongation growth and accumulation of phenolic acids in the leaves.

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