|Authors: ||J.C. Pech, F. El-Yahyaoui, A. Bernadac, A. Latché, B. Flores, F. Romojaro|
|Keywords: ||Cucumis melo, ethylene sensitivity, aroma volatiles, softening, degreening, respiratory climacteric|
Charentais melons (Cucumis melo, var cantalupensis) in which ethylene biosynthesis has been suppressed by an antisense ACC oxidase gene have been used to better understand the role of ethylene in the regulation of the ripening process of climacteric fruit and on the development of sensory qualities.
We have shown that a number of biochemical and molecular processes associated with the ripening of climacteric fruit are ethylene-independent.
In some cases, such as softening of the flesh, the same pathway comprises both ethylene-dependent and -independent components.
The various ethylene-dependent events exhibit differential sensitivity to ethylene.
The threshold level for degreening of the rind is 1 ppm, while 2.5 ppm are required to trigger the ethylene-dependent component of the softening process.
The saturating level of ethylene for all these events is less than 5 ppm, which is far lower than the internal ethylene concentrations found in the fruit at the climacteric peak (around 100 ppm). Detachment of the fruit influences the development of respiratory climacteric.
Fruit remaining attached to the vine, although producing higher levels of ethylene, exhibit a reduced climacteric rise in respiration as compared to detached fruit.
The response of antisense ACC oxidase fruit to exogenous ethylene, in terms of respiration, is higher in detached than in attached fruit.
Ethylene-suppressed melons show a severe reduction of aroma volatiles production, particularly in ester production.
In the biosynthetic pathway of aliphatic esters, the reduction of fatty acids and aldehydes appears to be ethylene-dependent.
In contrast, alcohol acetylation comprises ethylene-dependent and ethylene-independent components, probably corresponding to differentially regulated alcohol acetyl transferases.
In terms of sensory quality, these data show that the extension of shelf-life through the inhibition of ethylene production has some beneficial effects on texture and sugar accumulation but is detrimental for the generation of aroma.
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