Evidence for cross-linking in tomato cutin using HR-MAS NMR spectroscopy

• Published in: Phytochemistry (Oxford) 2003-11, Vol.64 (6), p.1163-1170
• Main Authors: Deshmukh, Ashish P., Simpson, André J., Hatcher, Patrick G.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; biopolymers; Biopolymers - chemistry; Branched carboxylic acids; carboxylic acids; Chemical constitution; chemical structure; cutin; Esters; fatty acids; Fruit - chemistry; fruits (plant anatomy); Fundamental and applied biological sciences. Psychology; HR-MAS NMR spectroscopy; Keywords; Lycopersicon esculentum; Lycopersicon esculentum - chemistry; Membrane Lipids - chemistry; nuclear magnetic resonance spectroscopy; Nuclear Magnetic Resonance, Biomolecular - methods; phytochemicals; plant extracts; Plant physiology and development; polyesters; Polyesters - chemistry; Solanaceae; Solanum lycopersicum var. lycopersicum; spectral analysis; Tomato; tomatoes; vegetable crops
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/S0031-9422(03)00505-3

Cutin is a polyester biopolymer component of plant leaf and fruit cuticles, most often associated with waxes and cuticular polysaccharides, and sometimes with another aliphatic biopolymer called cutan. Insolubility of these cuticular biopolymers has made it difficult to apply traditional analytical techniques for structure determination, because most techniques providing molecular level details require solubility. By using the relatively new technique of one and two-dimensional high-resolution magic angle spinning (HR-MAS) NMR spectroscopy, with added information from solid-state 13C NMR spectroscopy, detailed through-bond connectivities and assignments are made for cutin from Lycopersicon esculentum (tomato) fruit. Based on the data obtained, tomato cutin is found to be predominantly an aliphatic polyester with some olefinic and aromatic moieties, consistent with previous studies that employed various degradative approaches. Aside from esters, there are free primary and secondary alcohol groups, as well as free fatty acids. A significant finding is the presence of α-branched fatty acids/esters. Mid-chain hydroxyls appear to be generally unesterified, but esters of mid-chain hydroxyls have been identified. The α-branched fatty acids/esters and esters of mid-chain hydroxyls could point towards cross-linking. Structure of intact cutin from Lycopersicon esculentum fruit cuticle, swollen in DMSO, was determined using high-resolution magic angle spinning (HR-MAS) NMR spectroscopy, showing mainly esters, primary and secondary alcohols, fatty acids, and in addition, functionalities such as α-branched carboxylic acids, and esters of mid-chain alcohols showing possible cross-linking sites.