Altitudinal variation of secondary metabolites in flowering heads of the Asteraceae: trends and causes
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Plants in alpine habitats are exposed to severe environmental stresses including temperature and radiation extremes. The observation that flowering heads from high altitude populations of Scorzoneroides helvetica (Mérat) J.Holub (synonym: Leontodon helveticus Mérat) contained higher amounts of luteolin derivatives than conspecific populations in lower altitudes prompted further investigations. An elevational increase of phenolics was confirmed in flowering heads of neophytic populations of three additional taxa of the Cichorieae tribe in New Zealand. A solely genetic basis of the altitudinal trends of flavonoids and phenolic acids was eliminated by field experiments with cultivars of the medicinal herbs Arnica montana L. and Matricaria chamomilla L. planted at nine different altitudes ranging from 600 to 2,200 m in the Tyrolean Alps. Parallel experiments on potted plants excluded soil characteristics as the factor causing the observed variation. The initial hypotheses that enhanced UV-B radiation in higher altitudes was triggering an increase in the ratio of B-ring-ortho-diphenolic versus B-ring-monophenolic flavonols in flowering heads of Arnica was disproved by climate chamber experiments resulting in no significant difference between plants grown in ambient and threefold ambient UV-B radiation regimes. In contrast, an increase of this ratio similar to the changes observed in higher altitudes resulted from a decrease in temperature by 5°C in a second climate chamber experiment. Conclusively, enhanced UV-B radiation is probably not the key factor inducing shifts in the phenolic composition in Asteraceae growing at higher altitudes but it is rather the temperature which decreases with altitude.
KeywordsAntioxidants Chemical ecology Free radicals Temperature UV-B radiation
The author is indebted to Serhat Cicek and Renate Spitaler (both Innsbruck) for fruitful discussions and proofreading.
- Bornman JF, Reuber S, Cen YP, Weissenböck G (1997) Ultraviolet radiation as a stress factor and the role of protective pigments. In: Lumsden P (ed) Plants and UV-B: responses to environmental change. Cambridge University Press, Cambridge, pp 157–168Google Scholar
- Körner C (1999) Alpine plant life. Functional plant ecology of high mountain ecosystems. Springer, BerlinGoogle Scholar
- Makepeace W (1981) Polymorphism and the chromosomal number of Hieracium pilosella in New Zealand. N Z J Bot 19:255–258Google Scholar
- Nagy L, Grabherr G (2009) The biology of Alpine habitats. Oxford University Press, OxfordGoogle Scholar