Polyamines and their cellular anti-senescence properties in honey dew muskmelon fruit.

Activated oxygen free radicals cause peroxidative damage to all membranes and hasten senescence. Polyamines (PAs) are effective scavengers of these free radicals produced by lipoxygenase (LOX) and phospholipase-D (PL-D). Five days prior to abscission (harvest), 'Honey Brew' (Cucumis melo L. (Inodorus group)) fruit have a change in the ratio of endogenous spermidine (SPD) to putrescine (PUT), from SPD>PUT to SPD<PUT, which coincides with the onset of fruit senescence. Hypodermal-mesocarp tissues from harvested fruit incubated in mannitol with exogenous SPD or spermine, at 0.25 or 0.5 M, had more chlorophyll (less senescence) following 6 or 48 h of darkness than tissues incubated in mannitol without PAs. Polyamine-incubated tissues versus no PA has less membrane peroxidation as indicated by less malondialdehyde production, and LOX and PL-D activities, and less plasma membrane perturbation as indicated by greater H(+)-ATPase activity, and protein and phospholipid contents. Prolonging the duration of endogenous SPD content, whereby, it is greater then PUT content, in harvested (fully-ripened) 'Honey Brew' fruit, could delay melon senescence and promote a longer marketable life.