Ripening of tomato fruit locule gel tissue in response to ethylene

Ethylene production by locule gel tissue excised from immature tomato fruit was inhibited by exposure to 4.5 mmol l C2H4, and 1-aminocyclopropane-1-carboxylic acid (ACC) content was reduced. In contrast, CO2 production, ethylene forming capacity (EFC), red colour development, tissue liquefaction and seed maturation as measured by subsequent germination rate were stimulated by C2H4, and, in immature gel, the onset of autocatalytic C2H4 production was hastened. The autoinhibition of C2H4 production in immature locule gel tissue required continuous exposure to C2H4, as transfer to air and then back to C2H4 resulted in C2H4 production first increasing to control levels, then decreasing again. Locule gel tissue from pink fruit however, responded to C2H4 treatment with increased C2H4 and CO2 production, but ACC levels were unchanged. Inhibition of C2H4 action by pretreatment with STS inhibited both autoinhibition and autostimulation of C2H4 production in immature and mature gel tissues, respectively. These results indicate that there is a transition from a negative to a positive feedback mechanism of C2H4 on C2H4 biosynthesis in locule gel during ripening. Control of this feedback mechanism, which involves ACC synthesis, may be separate from that of other manifestations of C2H4 action. © 2000 Elsevier Science B.V. All rights reserved.