Tissue blackening
occurs through the action of copper containing oxidase
enzymes (e.g. polyphenoloxidases and tyrosinases) which are
released or synthesised and presented with oxidative
conditions when tissues are wounded.
Substrates
for these enzymes vary in different tissue.
Enzymes
and substrates are normally retained within different
compartments and come together when cells are injured or
moribund.
Phenols
have an important natural function in regulating IAA oxidation
(auxin protector).
The
toxicity of phenols is probably due mainly to reversible
hydrogen bonding to proteins.
Irreparable growth
inhibition occurs when phenols are oxidised to highly active
quinone compounds which then cyclise, polymerise and/or oxidise
proteins to form increasingly melanic compounds.
