The effects of ethylene, depressed oxygen and elevated carbon dioxide on antioxidant profiles of senescing spinach leaves

It has been suggested that antioxidants play a role in regulating or modula ting senescence dynamics of plant tissues. Ethylene has been shown to promo te early plant senescence while controlled atmospheres (CA; reduced O-2 lev els and elevated CO2 levels) can delay its onset and/or severity. In order to examine the possible importance of various antioxidants in the regulatio n of senescence, detached spinach (Spinacia oleracea L.) leaves were stored for 35 d at 10 degrees C in one of three different atmospheres: (1) ambien t air (0.3% CO2, 21.5% O-2, 78.5% N-2), (2) ambient air + 10 ppm ethylene t o promote senescence, or (3) CA (10% CO2, 0.8% O-2 and 89.2% N-2) to delay senescence. At weekly intervals, material was assessed for activities of th e antioxidant enzymes ascorbate peroxidase (ASPX; EC 1.11.1.11), catalase ( CAT; EC 1.11.1.6), dehydroascorbate reductase (DHAR; EC 1.8.5.4), glutathio ne reductase (GR; EC 1.6.4.2), monodehydroascorbate reductase (MDHAR; EC 1. 6.5.4), and superoxide dismutase (SOD; EC 1.15.1.1), and concentrations of the water-soluble antioxidant compounds ascorbate and glutathione. Indicato rs of the rate and severity of senescence (lipid peroxidation, chlorophyll, and soluble protein levels) were also determined. Results indicated that t he rate and severity of senescence was similar between the leaves stored in ambient air or CA until day 35, at which point the ambient air-stored leav es exhibited a sharp increase in lipid peroxidation, Tissues under both sto rage regimes demonstrated significant declines only in levels of ASPX, CAT, and ascorbate. Glutathione content in the CA-stored tissue also significan tly dropped, but only on day 35, In contrast, spinach leaves stored in ambi ent air + ethylene experienced a rapid decrease in levels of all the antiox idants assessed except SOD. Declines in levels of ASPX, CAT, and ascorbate over the 35 d storage period regardless of the composition of the storage a tmosphere suggests that regulation of H2O2 levels plays an important role i n both the dynamics and severity of post-harvest senescence of spinach.