Harvest date affects the antioxidative systems in pear fruits

摘要

Pears (Pyrus communis L. cv. Conference) were picked 7 d before (-7 d), during (0) or 7 d (+7 d) after the estimated ideal time for commercial harvest. Changes in antioxidant content (ascorbate and glutathione) and in the activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), total peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR) were estimated immediately after harvest for each picking time. Ascorbate and non-protein thiols (glutathione) content significantly decreased with increasing maturity. Concommitantly, the activity of SOD and CAT fell about five-fold and two-fold, respectively, when the fruit was picked more mature, indicating a higher potential for the accumulation of cytotoxic O_2~- and H_2O_2 respectively. POX activity remained relatively constant until the optimal harvest date but increased later. APX activity increased 2.5-fold in the more mature fruit but GR remained stable. Collectively, these results provide evidence that harvest date is accompanied by a decline in the non-enzymic and enzymic systems responsible for catabolism of active oxygen species. This may contribute to explain the widely described influence of harvest date on the occurrence of physiological disorders in pears.