Abstract
A change in the metabolism of hydroxycinnamic acids in wounded tomato fruits (Lycopersicon esculentum).Healing of lesions in tomato fruits (Lycopersicon esculentum Mill. var. cerasiforme) is partly due to lignification of cells bordering the wounded zones. The pericarp of healthy fruits contains a high level of hydroxycinnamic derivatives but never shows lignification. Thus, the reaction of the fruit to wounding seems to be a change in the metabolism, leading to the formation of monomeric units of which lignins are constituted. Hydroxycinnamate:CoA ligase (EC 6.2.1.12; CL) and O‐methyltransferase (EC 2.1.1.6; OMT) appear to play an important role in this change. In wounded fruits CL acts preferentially on p‐coumarate and ferulate as compared to caffeate, and OMT is particularly active with 5‐OH ferulate as substrate. These changes lead to the formation of p‐coumaroyl CoA, feruloyl CoA and sinapate, which are incorporated into lignin. Phenylalanine ammonialyase (EC 4.3.1.5) and glucosyltransferase activities increase greatly after wounding, whereas the activity of hydroxycinnamoyl‐CoA:quinate hydroxycinnamoyl transferase decreases. These data complement those previously reported on peroxidases and suggest that, after the increase of enzyme activities, monomeric units are formed and then polymerized by some peroxidases specific for lignification.
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