DETERMINATION AND INVOLVEMENT OF AQUEOUS REDUCING COMPOUNDS IN OXIDATIVE DEFENSE SYSTEMS OF VARIOUS SENESCING LEAVES

A method for determining different types of reducing activity in aqueo us leaf extracts of various edible herb species [watercress (Rorippa n asturtium-aquaticum), parsley (Petroselinum crispum), basil (Ocimum ba silicum), and sage (Salvia officinalis L.)] was developed. This method , based on kinetics of the reduction of Fe(III) to Fe(II), was employe d to study the correlation between leaf senescence rates under darknes s and their relative reducing capacity in aqueous extracts, which repr esents an oxidative defense mechanism. Evidence is presented showing t hat the total reducing capacity is negatively correlated with the rela tive senescence rate of these four herb species and thereby provides a means to predict their storage potential. Also, the initiation of sen escence processes was associated with a weakening of the oxidative def ense systems. Exogenous application of active reducing agents (morin, ferulic acid, kaempferol, and glutathione) inhibited significantly chl orophyll degradation of detached parsley leaves to an extent related t o their in vitro effectiveness of reducing activity. The results furth er emphasize the correlation between decreasing senescence rate and in creasing reducing activity, thereby confirming the possible involvemen t of reducing compounds in oxidative defense systems of various edible senescing leaves.