plant surface microbiology.pdf

25 Methods for Analysing the Interactions Between
Epiphyllic Microorganisms and Leaf Cuticles
Daniel Knoll and Lukas Schreiber
1 Introduction
The plant cuticle forms the solid surface environment for epiphyllic microorganisms.
This chapter presents newly developed techniques for analysing the
interactions between epiphyllic microorganisms and leaf cuticles. The methods
take into account the unique physical, chemical and functional characteristics
of the cuticular interface of leaves. Furthermore, a new experimental
approach simulating leaf surface microbe interactions on the basis of isolated
cuticular membranes (CM) will be presented. Changes in cuticular properties
in relation to microbial growth can be assessed in vitro under controlled conditions.
2 Physical Characterisation of Cuticle Surfaces by Contact
Angle Measurements
Surface wetting can be determined quantitatively by measuring the contact
angle s of an aqueous droplet applied to a surface. The contact angle s is
defined by the angle (°) between the flat leaf surface and the line tangent to a
water droplet through the point of contact as demonstrated in Fig. 1. The size
of the contact angle s is directly related to the hydrophobic properties of a
surface. Low contact angles indicate well wettable surfaces (left-hand side of
Fig. 1), whereas high contact angles indicate little wettable surfaces (righthand
side of Fig. 1). Generally, advancing contact angles are measured with
the aid of a goniometer within the first minute after application of a droplet
onto the surface. The droplet volume may vary from 1 to 10 ml, since it has
been previously shown that contact angles were independent of the droplet
size (Schreiber 1996). However, contact angles can be significantly dependent
on the pH values of the buffered aqueous solutions. So-called contact angle
titration measuring contact angles at different pH values ranging between pH
Plant Surface Microbiology
A.Varma, L. Abbott, D. Werner, R. Hampp (Eds.)
© Springer-Verlag Berlin Heidelberg 2004