AOBPreview originally published online on March 12, 2003
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Annals of Botany 91: 643-655, 2003
© 2003 Annals of Botany Company
Comparative Analysis of Leaf Trichome Structure and Composition of Epicuticular Flavonoids in Finnish Birch Species
1 Section of Ecology, Department of Biology, University of Turku, FIN-20014 Turku, Finland, 2 Laboratory of Electron Microscopy, University of Turku, FIN-20014 Turku, Finland and 3 Laboratory of Environmental Chemistry, Department of Chemistry, University of Turku, FIN-20014 Turku, Finland
* For correspondence at: University of Turku, Section of Ecology, Department of Biology, FIN-20014, Turku, Finland. Fax + 358 2 3336550, e-mail elekos{at}utu.fi
Received: 4 December 2002; Returned for revision: 13 January 2002; Accepted: 24 January 2003 Published electronically: 12 March 2003
The morphology, ultrastructure, density and distribution of trichomes on leaves of Betula pendula, B. pubescens ssp. pubescens, B. pubescens ssp. czerepanovii and B. nana were examined by means of light, scanning and transmission electron microscopy. The composition of flavonoids in ethanolic leaf surface extracts was analysed by high pressure liquid chromatography. All taxa examined contained both glandular and non-glandular trichomes (short and/or long hairs) but differed from each other in trichome ultrastructure, density and location on the leaf. Leaves of B. pubescens were more hairy than those of B. pendula, but the latter species had a higher density of glandular trichomes. Of the two subspecies of B. pubescens, leaves of ssp. pubescens had more short hairs on the leaf surface and four times the density of glandular trichomes of leaves of ssp. czerepanovii, whereas, in the latter subspecies, short hairs occurred largely on leaf veins, as in B. nana. The glandular trichomes were peltate glands, consisting of medullar and cortical cells, which differed structurally. Cortical cells possessed numerous small, poorly developed plastids and small vacuoles, whereas medullar cells had several large plastids with well-developed thylakoid systems and fewer vacuoles. In B. pubescens subspecies, vacuoles of the glandular cells contained osmiophilic deposits, which were probably phenolic, whereas in B. pendula, vacuoles of glandular trichomes were characterized by the presence of numerous myelin-like membranes. The composition of epicuticular flavonoids also differed among species. The two subspecies of B. pubescens and B. nana shared the same 12 compounds, but five of these occurred only in trace amounts in B. nana. Leaf surface extracts of B. pendula contained just six flavonoids, three of which occurred only in this species. In summary, the structure, density and distribution of leaf trichomes and the composition of epicuticular flavonoids represent good taxonomic markers for Finnish birch species.
Key words: Betula pendula, silver birch, Betula pubescens ssp. pubescens, white birch, Betula pubescens ssp. czerepanovii, mountain birch, Betula nana, dwarf birch, non-glandular trichomes, glandular trichomes, ultrastructure, flavonoids.
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