Protein fruit ripening

Fruit tissues respond to ethylene by exhibiting increases in the activities of enzymes that catalyze ripening reactions, and in some cases, the increases in enzyme activity probably are the result of de novo synthesis, rather than activation of preexisting enzymes. Other target tissues respond similarly to ethylene. But it is not known whether ethylene acts directly to evoke new enzyme production. Interpretation of results with inhibitors of RNA and protein synthesis is inconclusive, because it could be merely that RNA and protein synthesis are essential to maintain the cells in a state competent to respond to ethylene. Moreover, there are some responses to ethylene, besides fruit ripening, which occur under conditions which apparently do not directly involve RNA and protein synthesis (e.g., membrane permeability changes). It has been proposed that the in vivo ethylene receptor site contains a metal such as copper (34,35). 

Salzman, R.A., Tikhonova, I., Bordelon, B.P., Hasegawa, P.M. and Bressan, R.A. (1998) Coordinate accumulation of antifungal proteins and hexoses constitutes a developmental controlled defence response during fruit ripening in grape, Plant Physiol., 117, 465-472. 

Unlike papain, fruit bromelain does not disappear as the fruit ripens. Fruit and stem bromelains are acidic and hasic proteins, resp. uv max (stem) 280 nm (A 20.1). 

A further consideration in the choice of gene relates to those that are members of a gene family. Only one member of such a family may be involved in carotenogenesis in a particular tissue. A good example of this is Psy-1 and-2 of tomato. PSY-1 is responsible for phytoene synthesis in ripening fruit (Fraser et al, 1999) whereas PSY-2 is not functional in chromoplasts, even if the protein is produced. 

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