Water and Solute Permeability of Plant Cuticles: Measurement and ...

1.2 Cutin Composition 5
Table 1.2 Common C16- and C18-monomers occurring in the polymer matrix of several plant
species
Compound Chemical Structure
C16-monomers
Palmitic acid
Palmitic alcohol
CH 3
CH3
16-Hydroxypalmitic acid OHCH2
1,16-Palmitic diacid
9,16-Dihydroxypalmitic acid
10,16-Dihydroxypalmitic acid
C18-monomers
Stearic acid CH3
Stearic alcohol CH3
18-Hydroxystearic acid OHCH2
9,10,18-Trihydroxystearic acid OHCH2
COOH
OHCH2
OHCH2
OH
OH
OH
OH
COOH
CH2OH
COOH
COOH
COOH
COOH
COOH
CH2OH
COOH
COOH
18-Hydroxy-9,10-epoxystearic acid COOH
OHCH 2
O
C18 unsaturated dicarboxylic acids (Nawrath 2006), which does not fit the picture
of cutin composition derived from all previous investigations (Table 1.2).
Unfortunately, barrier properties of this type of “atypical” cutin have not yet been
characterised. Thus, one should be cautious before generalising cutin composition
obtained by transesterification of MX of plant species from which CM can be
isolated. This may represent a specific set of cutins characteristic of isolable cuticles.
We are searching for the relationship between chemistry and structure of cuticles
and their permeability to water and solutes. Permeability of a membrane is related to
structure, which in turn depends on chemical composition. Unfortunately, we could
not find any study relating the above cutin classification to water or solute permeability.
Number, type and distribution of polar functional groups in the polymer,
crystallinity, and the prevalence of the glassy and rubbery states at physiological
temperatures are important properties. In composite polymers, the mutual arrangement
of the various polymers is also important. Simply looking at the products
obtained by transesterification or acid hydrolysis reveals little about the structure
and function of the polymer.
The monomer composition does not tell us much about the original composition
of the polymer and the way the monomers were cross-linked and arranged in the
MX. The cutin models which are based on type and predominance of cutin acids