AOBPreview published online on June 28, 2004
Annals of Botany, doi:10.1093/aob/mch131
© 2004 by Annals of Botany Company
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1 Section of Ecology, Department of Biology, University of Turku, FIN-20014 Turku, Finland; Laboratory of Electron Microscopy, University of Turku, FIN-20014 Turku, Finland
* To whom correspondence should be addressed. E-mail: elekos{at}utu.fi.
• Background and Aims Changes in number of trichomes and in composition and concentrations of their exudates throughout leaf development may have important consequences for plant adaptation to abiotic and biotic factors. In the present study, seasonal changes in leaf trichomes and epicuticular flavonoid aglycones in three Finnish birch taxa (Betula pendula, B. pubescens ssp. pubescens, and B. pubescens ssp. czerepanovii) were followed. • Methods Trichome number and ultrastructure were studied by means of light, scanning and transmission electron microscopy, while flavonoid aglycones in ethanolic leaf surface extracts were analysed by high-pressure liquid chromatography. • Key Results Density of both glandular and non-glandular trichomes decreased drastically with leaf expansion while the total number of trichomes per leaf remained constant, indicating that the final number of trichomes is established early in leaf development. Cells of glandular trichomes differentiate before those of the epidermis and produce secreted material only during the relatively short period (around 1-2 weeks) of leaf unfolding and expansion. In fully expanded leaves, glandular trichomes appeared to be at the post-secretory phase and function mainly as storage organs; they contained lipid droplets and osmiophilic material (probably phenolics). Concentrations (mg g-1 d. wt) of surface flavonoids decreased with leaf age in all taxa. However, the changes in total amount (µg per leaf) of flavonoids during leaf development were taxon-specific: no changes in B. pubescens ssp. czerepanovii, increase in B. pendula and in B. pubescens ssp. pubescens followed by the decline in the latter taxon. Concentrations of most of the individual leaf surface flavonoids correlated positively with the density of glandular trichomes within species, suggesting the participation of glandular trichomes in production of surface flavonoids. • Conclusions Rapid decline in the density of leaf trichomes and in the concentrations of flavonoid aglycones with leaf age suggests that the functional role of trichomes is likely to be most important at the early stages of birch leaf development.
Revised March 16, 2004
Accepted March 24, 2004
Article
Changes in Leaf Trichomes and Epicuticular Flavonoids during Leaf Development in Three Birch Taxa
2 Laboratory of Environmental Chemistry, Department of Chemistry, University of Turku, FIN-20014 Turku, Finland
3 Section of Ecology, Department of Biology, University of Turku, FIN-20014 Turku, Finland
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