plant surface microbiology.pdf

9 Interactions Between Epiphyllic Microorganisms and Leaf Cuticles 147
Fig. 2. A scheme of the phyllosphere
as a habitat for
microorganisms showing most
of the relevant climatic and
plant parameters determining
the living conditions of the leaf
surface
atmosphere
waxes
cutin
epidermal
wall
wetting
biofilm
penetration
leaching
(Andrews 1992; Jacques and Morris 1995; Fiss et al. 2000). However, looking
at the leaf surface as a microhabitat with very specific boundary conditions,
investigations of the parameters, limitations and interactions between the
lipophilic leaf surface and the microorganisms have rarely been carried out
(Fig. 2). This habitat is characterised by an extreme microclimate due to
large variations in climatic parameters like light intensity and temperature
(Andrews and Harris 2000). Due to specific physical, chemical and biological
properties of leaf surfaces, the phyllosphere is also dominated by a low
availability of water and nutrients (Schönherr and Baur 1996; Beattie and
Lindow 1999). Investigating the microbial ecology of the phyllosphere will be
a combined approach including plant ecophysiological and microbiological
tools. In the following, several important aspects of the microbial ecology of
the phyllosphere will be discussed and selected examples for the interactions
occurring between epiphyllic microorganisms and the leaf surface will be
given.
2 Physical and Chemical Parameters of the Phyllosphere
water
vapor
gradient
The plant cuticle covering the leaf surface is a lipophilic, extracellular
biopolymer. It is composed of the cutin polymer (Kolattukudy 2001), which is
a polyester of esterified hydroxy fatty acids, and of cuticular waxes (Walton
1990), deposited as monomeric compounds to the cutin polymer (intracuticular
waxes) and to the cutin surface (epicuticular waxes). Cuticular waxes are
basically linear long chain aliphatic compounds of different chain length and
different substance classes. Typical wax constituents are alkanes, aldehydes,
primary and secondary alcohols, acids and esters composed of the respective
acids and alcohols (Bianchi 1995). Besides these linear long-chain aliphatics,