plant surface microbiology.pdf

9 Interactions Between Epiphyllic Microorganisms and Leaf Cuticles 151
(Fig. 4A). Maximum effects were a decrease of the contact angle from about
95° to 30° at a coverage of 70 %. Similar results were obtained when clean ivy
leaf surfaces were colonised by bacteria. A bacterial coverage of 10 % of the
leaf surface resulted in a decrease in the contact angle by 25° and only a 25 %
coverage resulted in decrease from 90° to 40° (Fig. 4B). These experiments
clearly proved that leaf surface wetting properties can be altered to a large
degree by the presence of epiphyllic microorganisms.
Using scanning electron microscopy, gas chromatography and contact
angle measurements in parallel, investigation of needle (Abies grandis Lindl.)
and leaf surfaces (Juglans regia L.) during one season supported this observation
(Schreiber 1996; Knoll and Schreiber 1998). The pronounced increase in
Contact angle (degree)
contact angle (degree)
100
90
80
70
60
50
40
30
20
80
76
72
68
64
60
56
Silanized
glass
pH 3.0
surface
pH 9.0
20/6/1994
20/7/1994
15/8/1994
Abies
grandis
current year needles
pH 3.0
pH 9.0
15/10/1994
180 200 220 240 260 280 300 320
day of the year 1994
A
(a) t = 6 h
0 10 20 30 40 50 60 70 80
Area covered by P. fluorescens (%)
15/11/1994
C
Contact angle (degree)
Contact angle (degree)
80
75
70
65
60
55
50
45
40
100
90
80
70
60
50
40
30
Hedera
helix
0 5 10 15 20 25 30
Area covered by epiphytic micro-organisms (%)
5
6
/
9
0
/
2
5
5
7
/
9
0
/
1
9
Juglans
regia
8
/
9
0
/
2
1
160 180 200 220 240 260 280 300
5
Julian day (1995)
Fig. 4. Degree of wetting of a silanised glass surface (A) and an ivy (Hedera helix L.) leaf
surface (B) as a function of the coverage of the leaf surface with epiphyllic microorganisms.
Seasonal increase of needle (Abies grandis Lindl.) surface (C) and leaf (Juglans
regia L.) surface (D) wetting due to increasing amounts of microorganisms growing in
the phyllosphere
5
9
/
9
0
/
1
1
B
D
5
0
/
9
1
/
0
5