plant surface microbiology.pdf

9 Interactions Between Epiphyllic Microorganisms
and Leaf Cuticles
Lukas Schreiber, Ursula Krimm and Daniel Knoll
1 Introduction
Leaves of higher plants are exposed to the atmosphere. Due to the pronounced
two-dimensional structure of leaves, the surface area of plants is significantly
enlarged. This allows an efficient absorption of visible light used in photosynthesis
and it supports the rapid gas exchange of carbon dioxide and oxygen,
occurring across stomates. With most leaves, stomates representing small
pores, cover only between 0.5 to 1 % of the total leaf surface area (Larcher
1996), whereas the largest part of the leaf surface is covered by the plant cuticle
forming the major interface between the leaves and the atmosphere (Kerstiens
1996). The cuticle developed during evolution when plants moved from
their aqueous habitats to the dry land. It protects land living plants from desiccation.
The water potential in the atmosphere is nearly always lower than the
water potential of plants, which causes a constant driving force for the flow of
water from the plant body to the atmosphere (Nobel 1991). Without the cuticle
forming a very efficient transport barrier for the passive diffusion of water
from the turgescent plant to the atmosphere, most of the land-living higher
plants would never be able to survive.
Besides this major function as a watertight barrier, the plant cuticle also
limits the leaching of ions and nutrients from the leaf interior (Tukey 1970),
and it forms a mechanical barrier for most microorganisms trying to infect
the living leaf tissues (Mendgen 1996; Schafer 1998). Looking at the surfaces
of healthy, green leaves collected in the environment in their natural habitats
using different microscopical techniques (fluorescence microscopy, confocal
laser scanning microscopy or scanning electron microscopy), it becomes
obvious that leaf surfaces are always covered by epiphyllic microorganisms to
a certain degree (Fig. 1). This epiphyllic flora is composed of bacteria, yeasts
and filamentous fungi belonging to different systematic categories (Morris et
al. 1996). The degree of coverage strongly depends on a series of parameters
like the plants species, the structure of the leaf surface, the habitat of the plant
and the age of the leaf (Preece and Dickinson 1971; Dickinson and Preece
Plant Surface Microbiology
A.Varma, L. Abbott, D. Werner, R. Hampp (Eds.)
© Springer-Verlag Berlin Heidelberg 2004