plant surface microbiology.pdf

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Lukas Schreiber, Ursula Krimm and Daniel Knoll
cuticular waxes of some plant species are dominated by a large degree by
triterpenoic acids and triterpenols (Gülz 1994; Markstädter et al. 2000). The
chemical environment which will be sensed by epiphyllic microorganisms living
on leaf surfaces will be the outermost layer of wax compounds forming
the true interface between the leaf and the atmosphere. For this reason, analytical
chemistry such as gas chromatography coupled to different detector
systems (FID and MS) is an important tool for describing the chemical environment
of the leaf surface (Riederer and Markstädter 1996).
Epicuticular waxes often form characteristic three-dimensional structures
like platelets (Fig. 3), rods, ribbons or filaments (Jeffree 1986). This significantly
increases leaf surface roughness. As a consequence, water drops, small
particles, as well as spores and bacterial cells located on the tips of these crystals
strongly reduce the attachment of particles to the leaf surface. Thus, rain
or water can simply wash off these loosely attached particles on rough leaf
surfaces (Barthlott and Neinhuis 1997). Both parameters, the very hydrophobic
nature of cutin and wax and the often very pronounced roughness of the
leaf surface, are responsible for the fact that leaf surfaces are a very dry habitat
since water is very efficiently rejected (Holloway 1970). Nevertheless, with
increasing leaf age in most cases epicuticular wax crystals tend to disappear,
probably due to erosion, and the factor roughness will become less significant
Fig. 3. Micrograph (SEM) of the upper astomatous leaf side of oak (Quercus robur L.)
showing the dense accumulation of epicuticular wax crystals. The crystals, having the
shape of small platelets, are oriented in a rectangular angle to the leaf surface leading to
a pronounced surface roughness