Prolongation of the shelf life of fruits and flowers

The gaseous substance ethylene is long known to influence the metabolism of plants especially during the ripening of fruits. This influence extends to the period of storage of agronomical products and thus constitutes an economical issue in trading. It is of major interest to control the residual metabolism of plant parts to prevent or delay spoilage. Substances counteracting the effects mediated by ethylene may be helpful to enhance the 'freshness' of food.

Recently it was found that nitric oxide is a natural plant growth regulator. Part of its senescence-delaying effect may be due to down regulating ethylene emissions. Moreover, harvested fruits and vegetables that were exposed to a nitric oxide containing atmosphere took on average twice the time to deteriorate to a commercially unacceptable state.

The nitric oxide molecule has an unpaired electron causing it to react immediately with oxygen. Treatments involving nitric oxide have to be done therefore in an otherwise pure nitrogen atmosphere, which somewhat limits the application. A workaround to increase the shelf life of e.g. cut flowers is the use of water-soluble substances generating nitric oxide like N-tert-butyl-alpha-phenylnitrone.

Experiments on the influence of NO on carnation indicate (besides ethylene effects) the enzyme guanyl cyclase to be involved in senescence regulation. The breakdown of cyclic guanosine monophosphate is retarded by sildenafil (a substituted guanine analogon), which indeed keeps cut flowers fresh for another week. A preserving effect on fruit and vegetables was also found, making sildenafil a promising agent. Today it is marketed under the trade name Viagra.