Characterization and biosynthesis of non-degradable polymers in plant cuticles.

The structure and monomeric composition of the highly aliphatic and non-saponifiable fraction of cutans isolated from the leaf cuticles of Agave americana L. and Clivia miniata Reg. have been elucidated. Spectroscopic Fourier transform infrared and 13C-nuclear magnetic resonance, calorimetric and X-ray diffraction studies, together with biopolymer analysis after exhaustive ozonolysis, showed that the cutan fraction consists of an amorphous three-dimensional network linked by ether bonds containing double bonds and free carboxylic acid functions. Data obtained from fatty acid sorption indicated that the new biopolymer investigated here has a highly hydrophobic character constituting an additional barrier biopolymer in those cuticles where it is present. Labelled [14C]linoleic acid was preferentially incorporated into the non-ester part of C. miniata leaf disks in comparison with the cutin fraction of the cuticular membrane. This indicates that the cis-pentadiene system of polyunsaturated fatty acids is involved in the formation of intramolecular linkages, mainly ether bonds, of the aliphatic biopolymer.