DECARBOXYLATIVE METABOLISM OF [1'-C-14]INDOLE-3-ACETIC ACID BY TOMATOPERICARP DISKS DURING RIPENING - EFFECTS OF WOUNDING AND ETHYLENE

The rate of decarboxylation of [1'-C-14]indole-3-acetic acid (IAA) inf iltrated into tomato (Lycopersicon esculentum Mill.) pericarp discs wa s much more rapid in green than in breaker and pink tissues. Studies w ere carried out in order to determine whether the decarboxylative cata bolism occurring in the green pericarp discs was associated with ripen ing or was a consequence of wound-induced peroxidase activity and/or e thylene production. After a 2-h lag, the decarboxylative capacity of t he green pericarp discs increased exponentially during a 24-h incubati on period. This increase was accompanied by increases in IAA-oxidase a ctivity in cell-free preparations from the intercellular space and cut surface of the discs. Although higher IAA-oxidase activity was detect ed in extracts from the tissue residue, which comprises mainly intrace llular peroxidases, this activity did not increase during the 24-h inc ubation period. Analysis of the cell-free preparations by isoelectric focusing revealed the major component in all samples was a highly anio nic peroxidase (pI = 3.5) the levels of which did not increase during incubation. However, the intercellular and cut-surface preparations co ntained additional anionic and cationic peroxidases which increased in parallel with the increases in both the IAA-oxidase activity of the p reparations and the decarboxylative capacity of the green pericarp dis cs from which they were derived. Treatment of green discs with the eth ylene-biosynthesis inhibitors aminooxyacetic acid and CoCl2, inhibited the development of an enhanced capacity to decarboxylate [1'-C-14]IAA but the inhibition was not counteracted by exogenous ethylene. Anothe r ethylene-biosynthesis inhibitor, aminoethoxyvinyl glycine, also redu ced ethylene levels but did not affect IAA decarboxylation, indicating that the decarboxylation was not a consequence of wound-induced ethyl ene production. The data obtained thus demonstrate that the enhanced c apacity to decarboxylate [1'-C-14]IAA that develops in green tomato pe ricarp discs following excision is not associated with ripening but in stead is attributable to a wound-induced increase in anionic and catio nic peroxidase activity in the intercellular fluid and at the cut surf ace of the excised tissues.