| Summary: | High concentrations (up to 2.4 mM) of long-lived, immobilized, organic free radicals were observed in column boundary layer (CBL) reaction zones at the boundary between fungal lesions and healthy, functional sapwood (xylem) in sycamore (Acer pseudoplatanus L.). These free radicals, with measured half-lives of up to 142 days at ambient temperature, were associated with the green polymeric material characteristically deposited in CBL reaction zones in this species, and may represent a novel category of chemical defence in plants. Such free radicals could contribute to the durable protection required in the bulky secondary tissues of living trees by acting as free radical scavengers, quenching the free radical chain reactions involved in the biodegradation of lignocellulose, thus protecting cell walls from decay and conferring a barrier function on the altered tissue. Reaction zone tissues were more resistant to decay and fungal colonization than normal A. pseudoplatanus sapwood.
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