plant surface microbiology.pdf

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Daniel Knoll and Lukas Schreiber
bers are additionally sealed with adhesive tape to avoid diffusion of water
through the sampling ports. Chambers are incubated upside down on dried
silica gel in an air-tight polyethylene box at 25 °C. The silica gel adsorbs all
free water of the air resulting in a water concentration inside the polyethylene
box constantly held at 0 %. Thus, the driving force DC for the water flow across
the cuticle corresponds to the density of water (10 3 kg m –3 ). The salt and sugar
concentration of the nutrition solution can be neglected as it does not affect
significantly the water activity a w. Control experiments showed that there was
no significant change in cuticular water permeability when using deionised
water or nutrition solution as the aqueous solution inside the chamber volume.
Sterilisation of cuticles by UV radiation also did not significantly change
water permeability.
4.5.2 Effect of Bacteria on Cuticular Water Permeability
Isolated cuticles are mounted in stainless steel chambers and permeability
coefficients P1 for water are determined for each sample as described above.
Cuticular permeability coefficients P1 determined after UV radiation ranged
between 1.44◊10 –10 m/s for Vinca major leaf cuticles and 10.8x10 –9 m/s for
Lycopersicon esculentum fruit cuticles (Table 1). Then cuticles are inoculated
with bacteria and incubated for 12 days in the incubation box at 25 °C at air
humidity close to 100 %. Control experiments are conducted by inoculating
the cuticles with 200 ml PBS in place of the bacterial cell solution. After incubation
with bacteria chambers are again transferred onto dried silica gel and
cuticular water permeability coefficients P2 are determined after an equilibrium
period of 1 day. The effects of bacteria on water permeability of the
respective cuticular membrane are calculated from the permeance of the cuticle
after treatment with bacteria (P2) divided by the initial permeance (P1).
Effect = P2
P1
Table 1. Cuticular permeability coefficients for water P water (m/s) from different plant
species. Values are arithmetic means with 95 % confidence intervals (ci) of 14 measured
permeability coefficients for each plant species
Species P water ¥10 –10 (m/s) ci 95 %x10 –10 (m/s)
Vinca major 1.44 1.26–1.64
Hedera helix can. 2.16 1.76–2.65
Prunus laurocerasus 2.93 2.34–3.68
Citrus aurantium 4.53 2.97–6.92
Lycopersicon esculentum 10.80 8.85–13.17