Changes in stomatal frequency and size during elongation of needles.

Screen Shot 2017-12-10 at 11.17.20
Epidermis of Tsuga heterophylla needle during ontogeny. (A) Stage 1 needle (completely in bud): stomata are visible at the apex indicated by the white circle (this region is enlarged at the right side). (B) Stage 2–3 needle (emerging from bud): more mature stomata are present at the apex in the white circle, but not in the basal and mid-section yet. (C) Stage 4 needle (fully emerged, not yet fully elongated): mature stomata are arranged in two bands on either side of the mid-vein on the entire needle; mature stomata and epidermal cells are depicted in detail on the right side. White arrows indicate stomata.


Changes in stomatal frequency and size during elongation of Tsuga heterophylla needles.

by Kouwenberg L. L. R., Kürschner W. M., Visscher H. (2004)

Lenny L. R. Kouwenberg,


Wolfram Michael Kürschner, University of Oslo, Department of Geosciences
Henk Visscher, Utrecht University, Department of Earth Sciences

in  Annals of Botany 94: 561-569 – –


• Background and Aims The inverse relationship between the number of stomata and atmospheric CO2levels observed in different plant species is increasingly used for reconstructions of past CO2concentrations. To validate this relationship, the potential influence of other environmental conditions and ontogenetical development stage on stomatal densities must be investigated as well. Quantitative data on the changes in stomatal density of conifers in relation to leaf development is reported.

• Methods Stomatal frequency and epidermal cells of Tsuga heterophylla needles during different stages of budburst were measured using computerized image analysis systems on light microscope slides.

• Key Results Stomata first appear in the apical region and subsequently spread basipetally towards the needle base during development. The number of stomatal rows on a needle does not change during ontogeny, but stomatal density decreases nonlinearly with increasing needle area, until about 50 % of the final needle area. The total number of stomata on the needle increases during the entire developmental period, indicating that stomatal and epidermal cell formation continues until the needle has matured completely.

• Conclusions Epidermal characteristics in developing conifer needles appear to be fundamentally different from angiosperm dicot leaves, where in general leaf expansion in the final stages is due to cell expansion rather than cell formation. The lack of further change in either stomatal density or stomatal density per millimetre needle length (the stomatal characteristic most sensitive to CO2 in conifers) in the final stages of leaf growth indicates that in conifers the stage of leaf maturation would not influence CO2 reconstructions based on stomatal density.

Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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