Ethylene feedback mechanisms in tomato and strawberry fruit tissues in relation to fruit ripening and climacteric patterns

Exposing pericarp tissue excised from immature tomato fruit to 4.5 mmol l C2H4 revealed a negative C2H4 feedback mechanism in relation to its biosynthesis since ACC concentration and C2H4 production by the tissue were reduced. An opposite trend (positive C2H4 feedback mechanism) was observed in pericarp tissue excised from fruit at the pink stage. At the mature-green stage however, tissue showed a transition from negative to positive C2H4 feedback mechanism with the onset of tissue ripening. In strawberry tissues excised from green, white and half-coloured fruits however, C2H4 application caused a short-term increase in C2H4 production followed by a sharp reduction to the control level along with a marked reduction in ACC levels. In both tomato and strawberry fruit tissues, C2H4 application significantly induced ACC oxidase (ACO) activity at all ripening stages, as measured by in vivo ACC conversion to C2H4. This strongly suggests that ACC synthesis is the limiting step in C2H4 autocatalysis and the only limiting step in C2H4 autoinhibition. In tomato pericarp tissues, C2H4 autoinhibition and autocatalysis caused by C2H4 application in immature and pink fruits, respectively, were eliminated when tissues were transferred to air and re-occurred when tissues were returned back to C2H4. These responses did not occur in all strawberry tissues due to the sharp reduction in C2H4 production with the time course of C2H4 application. Inhibiting C2H4 action with STS pretreatment inhibited both negative and positive C2H4 feedback mechanisms in both tomato and strawberry tissues indicating that C2H4 feedback mechanism is one sort of C2H4 action. In addition, only tomato fruit tissue showed significant increases in CO2 production with C2H4 application. In contrast to the nonclimacteric behaviour of strawberry fruit which exhibits only a negative C2H4 feedback mechanism, these data strongly suggest that the transition of the C2H4 feedback mechanism from negative to positive, which occurs in tomato fruit only with ripening initiation and progress, may be the reason behind the climacteric behaviour of tomato fruit. © 2000 Elsevier Science B.V. All rights reserved.