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Recent Developments on the Role of Ethylene in the Ripening ofClimacteric Fruit
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Edité par CCSD -
International audience. It has long been recognised that ethylene plays a major role in the ripeningprocess of climacteric fruit. A more thorough analysis, however, has revealed that anumber of biochemical and molecular processes associated with climacteric fruitripening are ethylene-independent. One of the crucial steps of the onset of ripeningis the induction of autocatalytic ethylene production. In ethylene-suppressed melons,ACC synthase activity is induced at the same time as in control melons, indicatingthat ACC biosynthesis during the early stages of ripening seems to be adevelopmentally-regulated (ethylene-independent) process. The various ripeningevents exhibit differential sensitivity to ethylene. For instance, the threshold level fordegreening of the rind is 1ppm, while 2.5 ppm are required to trigger somecomponents of the softening process. The saturating level of ethylene producingmaximum effects is less than 5 ppm, which is by far lower than the internal ethyleneconcentrations found in the fruit at the climacteric peak (over 100 ppm). In manyfruit chilling temperatures hasten ethylene production and ripening and in some lateseason pear varieties, exposure to chilling temperatures is even absolutely requiredfor the attainment of the capacity to synthesize autocatalytic ethylene. This iscorrelated with the stimulation of expression of ACC oxidase and of members of theACC synthase gene family. Ethylene operates via a perception and transductionpathway to induce the expression of genes responsible for the biochemical andphysiological changes observed during ripening. However, only a few genes inducedvia the ethylene transduction pathway have been described so far. We have used adifferential display method to isolate novel ethylene-reponsive (ER) cDNA clones oftomato that potentially play a role in propagating the ethylene response and inregulating fruit ripening. Collectively, these data permit a general scheme of themolecular mechanisms of fruit ripening to be proposed.
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