Submitted to: Phytochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/2003
Publication Date: N/A
Citation: Interpretive Summary: Cuts and scrapes provide avenues of infection by microorganisms. This is as true for people as well as plants. Wounds occurring at and after harvest predispose fruits and vegetables to decay. Injures in plants undergo a healing process that makes the wounds resistant to infection. This process is poorly understood, but it is often accompanied by production of material containing aldehyhdes. Because of this, the material was thought to be related to lignin. We used hydrolytic enzymes to remove cell wall material from healed injuries in grapefruit peel and analyzed this purified material by solid state NMR. This method identifies the primary chemical structures present in the sample. The healed tissue contained an abundance of aliphatic carbons, suggesting the material is more closely related to cutin or suberin, rather than lignin. This had not been suggested by previous research and will help guide further research on the chemical identity of this resistance associated material in plants.
Technical Abstract: There are conflicting views regarding the chemical composition of the induced, phloroglucinol-HCl (PG-HCl) reacting, material accumulating in injured citrus peel tissues. Grapefruit, Citrus paradisi, were injured, inoculated with Peicillium digitatum and incubated under contitions favorable to the accumulation of the defence related material. Solvent washed cell wall preparation of intact and injured-inoculated peel were further purified using hydrolytic enzymes. Histochemical examination revealed that the injury-inoculated samples contained PG-HCl reactive globular material in addition to the fragments of xylem and cuticle found in controls. The molecular composition of these samples were studied by 13C CP-MAS NMR. A complete assignement of the NMR signals was made. From the analysis evidence was found that cellulose and hemicellulose are the biopolymers present in the intact peel samples. The NMR difference spectrum intact-wounded peels showed resonances which were attributed to all major functional groups of the aromatic-aliphatic cutin polyester of new material produced by the wounds.