15.2 Occurrence in Nature
335
in recent years confirm that cutin is not only a compound restricted to terrestrial plants
but also is present in aquatic plants. This further revealed that the role of cutin in
aquatic plants is not for water retention, since aquatic plants have always abundance
of water and in fact have features to adapt them for growth in the environment. Cutin
in aquatic plants serves as a protective layer against UV radiation, pathogens and
environmental stress (Li et al. 2017). Because aquatic plants do not have the property
of terrestrial plant of being able to direct parts of their leaves to grow away from the
sun’s rays, they use cuticular matrix as a protection against UV.
Aquatic plants generally have the water facing sides and the sun-facing side.
Traces of suberin like compounds have been detected in the water facing side
(Borisjuk et al. 2018). Suberin is the polyester synthesized in the roots of vascular plants which aids in water retention. It is therefore conceivable that they are
present in the water facing sides of some aquatic plants. Further studies are yet to
fully define the roles or suberin in aquatic plants.
Cutin does not occur in all aquatic plants as not all aquatic plants have need for it.
Much is yet to be known about cutin in aquatic plants, and it has generated increasing
interest. Duckweed is one aquatic plant containing cutin which has attracted growing
interest for its potential commercial and ecological application. The cuticle contains
between 40 and 80% cutin by weight.
15.3 Chemistry of Cutin
Cutin is a polymer made up of C16 or C18 fatty acids with hydroxyl or epoxy groups
attached. The cutin polymer chains are cross-linked by ester linkages forming a
rather complex structure. It has polyester structure formed from the ester linkage
of C16 or C18 fatty acids binding with diols. The main monomer of cutin is the
10,16-dihydroxyhexadecanoic acid monomer (Graca and Lamosa 2010). Figure 15.2
shows ester linkages between this monomer and other hydroxyl compounds. Cutin
consists of different monomers covalently linked together as well as cross-linking
between different polymer chains. It is usually present in the form of a cutin matrix
with waxes and other compounds embedded within the matrix or as a layer within
the cuticle structure. Other components such as phenolic compounds could also be
present within the cutin matrix (Heredia 2003).
In a recent analysis of the biochemistry of aquatic plant cuticle, GC-MS analysis of
cutin extracted from duckweed fronds confirms the presence of a substantial amount
of fatty acids, and up to 95% of the cutin monomers were fatty acids. These include
saturated palmitic acid (C16) making up the bulk of the fatty acids. Cutin matrix
monomer also consisted of linolenic acid, an unsaturated C18 fatty acid which is
also an essential fatty acid for humans as it is not produced in the human body. Other
fatty acid components of cutin include other long-chain fully saturated fatty acids
as well as hydroxyl fatty acids, aromatic acids and phenolic ring-cinnamic acids
(Borisjuk et al. 2018). The wax fraction from the cuticle contains other valuable
compounds such as phytosterols and squalene which is a component of human skin
335
in recent years confirm that cutin is not only a compound restricted to terrestrial plants
but also is present in aquatic plants. This further revealed that the role of cutin in
aquatic plants is not for water retention, since aquatic plants have always abundance
of water and in fact have features to adapt them for growth in the environment. Cutin
in aquatic plants serves as a protective layer against UV radiation, pathogens and
environmental stress (Li et al. 2017). Because aquatic plants do not have the property
of terrestrial plant of being able to direct parts of their leaves to grow away from the
sun’s rays, they use cuticular matrix as a protection against UV.
Aquatic plants generally have the water facing sides and the sun-facing side.
Traces of suberin like compounds have been detected in the water facing side
(Borisjuk et al. 2018). Suberin is the polyester synthesized in the roots of vascular plants which aids in water retention. It is therefore conceivable that they are
present in the water facing sides of some aquatic plants. Further studies are yet to
fully define the roles or suberin in aquatic plants.
Cutin does not occur in all aquatic plants as not all aquatic plants have need for it.
Much is yet to be known about cutin in aquatic plants, and it has generated increasing
interest. Duckweed is one aquatic plant containing cutin which has attracted growing
interest for its potential commercial and ecological application. The cuticle contains
between 40 and 80% cutin by weight.
15.3 Chemistry of Cutin
Cutin is a polymer made up of C16 or C18 fatty acids with hydroxyl or epoxy groups
attached. The cutin polymer chains are cross-linked by ester linkages forming a
rather complex structure. It has polyester structure formed from the ester linkage
of C16 or C18 fatty acids binding with diols. The main monomer of cutin is the
10,16-dihydroxyhexadecanoic acid monomer (Graca and Lamosa 2010). Figure 15.2
shows ester linkages between this monomer and other hydroxyl compounds. Cutin
consists of different monomers covalently linked together as well as cross-linking
between different polymer chains. It is usually present in the form of a cutin matrix
with waxes and other compounds embedded within the matrix or as a layer within
the cuticle structure. Other components such as phenolic compounds could also be
present within the cutin matrix (Heredia 2003).
In a recent analysis of the biochemistry of aquatic plant cuticle, GC-MS analysis of
cutin extracted from duckweed fronds confirms the presence of a substantial amount
of fatty acids, and up to 95% of the cutin monomers were fatty acids. These include
saturated palmitic acid (C16) making up the bulk of the fatty acids. Cutin matrix
monomer also consisted of linolenic acid, an unsaturated C18 fatty acid which is
also an essential fatty acid for humans as it is not produced in the human body. Other
fatty acid components of cutin include other long-chain fully saturated fatty acids
as well as hydroxyl fatty acids, aromatic acids and phenolic ring-cinnamic acids
(Borisjuk et al. 2018). The wax fraction from the cuticle contains other valuable
compounds such as phytosterols and squalene which is a component of human skin