Journal of Experimental Botany, Vol 49, 739-746, Copyright © 1998 by Oxford University Press
G Karabourniotis
The anatomy and orientation of the foliar sclereids of the evergreen
sclerophyll Phillyrea latifolia suggest a
light-guiding function. Light microscope observations of enzymatically
isolated sclereids showed that they possessed very thick cell walls, lobes
and branches which occurred mainly at the end of the idioblasts reaching
the abaxial epidermis. Leaf cross-sections showed that sclereids occurred
diffusely within the mesophyll and were oriented vertically with respect to
the lamina. In paradermal sections, the cut cell walls of the sclereids
appeared as bright light spots among the dark-green background of the
mesophyll cells. The heterogeneity of the radiation field transmitted
through the same paradermal section was quantified by image analysis and
two- or three-dimensional representations. The amount of light transmitted
through the sclereids was found to be up to 30-fold higher compared to that
transmitted through the neighbouring mesophyll cells. The light guiding
capacity of the sclereids at the spongy mesophyll level was estimated to be
40-80%. In leaves illuminated from the adaxial surface, light passing
through the ends of the sclereids seemed to be reflected from the internal
surface of the abaxial epidermis. In sunny conditions when leaf thickness
tends to increase, the number of sclereids per unit leaf area was increased
significantly compared to the shaded ones. It is proposed that the anatomy
and orientation of the foliar osteosclereids of P.
latifolia, are suitable for a light-guiding function. Thus
foliar sclereids, besides other roles, may contribute both qualitatively
and quantitatively, to the enhancement of the light microenvironment within
the mesophyll of these sclerophyllous leaves.Keywords:
Phillyrea latifolia L. (incl. P.
media L.), foliar sclereids, light guiding, image analysis.
ARTICLES
Light-guiding function of foliar sclereids in the evergreen sclerophyll Phillyrea latifolia: a quantitative approach
Laboratory of Plant Physiology, Department of Agricultural Biology and Biotechnology, Agricultural University of Athens, Iera Odos 75, 11855 Botanikos, Athens, Greece; e-mail: karab@auadec.aua.ariadne.t.gr
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