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Pathological tissues from a variety of plants turn red when treated with the histochemical reagent phloroglucinol (PG)–HCl. This induced PG–HCl reacting material has been termed both wound gum and, more recently, induced lignin or lignin-like material. We are exploring alternative approaches to better identify this induced material. In this report, we describe methods for purifying the PG–HCl reactive material from solvent-washed tissue preparations and measuring the amount of p -coumaryl aldehyde released from the purified material by boiling in water. Acorn squash fruit wall tissue was sliced, sprayed with pectinase to elicit the formation of PG–HCl reactive material and incubated up to 72 h at 27°C. Sampled tissue was washed extensively with water and organic solvents. Insoluble residues were treated with cell wall degrading enzymes to remove cell wall materials, and dimethyl sulfoxide was used to dissolve starch. Yields of residual material increased from 7.5% in the time zero samples to 29.7% after 72 h. Refluxing the purified material in water released <6 μ g p -coumaryl aldehyde g−1 from preparations of tissue at time zero and 8100 μ g p -coumaryl aldehyde g−1 from samples incubated for 48 h. These results suggest that the function of the material is to sequester phytoalexins, but are not consistent with the material being lignin. Published by Elsevier Science Ltd. [Copyright &y& Elsevier]

Grapefruit, Citrus paradisi, were injured, inoculated with Penicillium digitatum and incubated under conditions favourable for the accumulation of defence related material. Histochemical examination revealed that tissues adjacent to inoculated injuries contained phloroglucinol-HCl (PG-HCl) reactive material. Solvent washed cell wall preparations of intact and injured-inoculated peel were further purified using a mixture of cell wall degrading enzymes. Samples from injured inoculated tissue contained PG-HCl reactive globular material in addition to the fragments of xylem and cuticle found in controls. The principal chemical moieties of the material that accumulates in grapefruit injuries during wound-healing were studied by solid state 13C cross-polarization magic angle spinning NMR. A complete assignment 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, in addition, relevant quantities of cutin were found in the residues of enzyme digest. The NMR difference spectrum intact- wounded peels showed resonances which were attributed to all major functional groups of the aromatic-aliphatic suberin polyester of new material produced by the wounds. Information on the latter polyester was obtained by analyzing the T1ρ (1H) relaxation. [Copyright &y& Elsevier]