Water and Solute Permeability of Plant Cuticles: Measurement and ...
Water and Solute Permeability of Plant Cuticles: Measurement and ...
Water and Solute Permeability of Plant Cuticles: Measurement and ...
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Chapter 4<br />
<strong>Water</strong> <strong>Permeability</strong><br />
All terrestrial organisms have a problem in common; they must minimise water<br />
loss to the atmosphere <strong>and</strong> prevent desiccation. The driving force <strong>of</strong> transpiration at<br />
25 ◦ C <strong>and</strong> 50% humidity is −95MPa, <strong>and</strong> at lower humidity it is even greater. <strong>Water</strong><br />
supply is <strong>of</strong>ten short. Higher plants, insects <strong>and</strong> mammals use similar strategies to<br />
save water. They have generated membranes <strong>of</strong> very low water permeability at their<br />
interface with the dry air surrounding them most <strong>of</strong> the time. Synthetic polymers<br />
used for membranes, tubing, containers <strong>and</strong> other packaging materials also have<br />
low permeability to gases, water <strong>and</strong> other solvents to protect goods. Before we turn<br />
to permeability <strong>of</strong> cuticles <strong>and</strong> to strategies <strong>of</strong> plants to built effective barriers for<br />
protection against adverse influences from the environment, we will briefly compare<br />
water permeability <strong>of</strong> synthetic membranes with permeance <strong>of</strong> plant polymer matrix<br />
membranes. Synthetic polymer membranes have been studied extensively during<br />
the last decades, <strong>and</strong> structure–permeability relationships have been established.<br />
What can we learn from homogeneous synthetic membranes to better underst<strong>and</strong><br />
permeability <strong>of</strong> heterogeneous plant cuticles?<br />
4.1 <strong>Water</strong> <strong>Permeability</strong> <strong>of</strong> Synthetic Polymer Membranes<br />
<strong>and</strong> Polymer Matrix Membranes: A Comparison<br />
<strong>of</strong> Barrier Properties<br />
<strong>Plant</strong> cuticles are polymeric membranes. The polymer matrix (MX) is composed <strong>of</strong><br />
lipophilic cutin <strong>and</strong> hydrophilic polar polymers (Sect. 1.1). Cutin is a polyester composed<br />
<strong>of</strong> hydroxyfatty acids, <strong>and</strong> depending on the number <strong>of</strong> hydroxyl groups <strong>and</strong><br />
extent <strong>of</strong> cross linking it contains 20–25% oxygen. The polymer matrix <strong>of</strong> tomato<br />
fruits is composed <strong>of</strong> carbon (67%), oxygen (23%), hydrogen (8.2%) <strong>and</strong> nitrogen<br />
(0.65). After acid hydrolysis, which eliminates polar polymers (polysaccharides,<br />
polypeptides <strong>and</strong> phenolic compounds), no nitrogen was found <strong>and</strong> elemental<br />
composition was 71% C, 20% O <strong>and</strong> 9.4% H (Schönherr <strong>and</strong> Bukovac 1973).<br />
This is very similar to the composition calculated for a linear polyester <strong>of</strong> C16<br />
L. Schreiber <strong>and</strong> J. Schönherr, <strong>Water</strong> <strong>and</strong> <strong>Solute</strong> <strong>Permeability</strong> <strong>of</strong> <strong>Plant</strong> <strong>Cuticles</strong>.<br />
© Springer-Verlag Berlin Heidelberg 2009<br />
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