Effect of enhanced oltraviolet-B radiation on fruit quality anddefense system of an-tioxidant enzyme in Mangifera indica L.cv.Tainong No.1
In order to explore the effects of enhanced UV-B radiation treatment on the quality of mango(Man-gifera indica L.)fruit and its antioxidant enzyme defense system,healthy Tainong No.1 adult mango trees were selected as experimental materials.The experiments were conducted in the field for two consecutive years,with a radiation intensity of 96 kJ·m-2·d-1 as treatment and natural sunlight as control(CK).The physiological and biochemical indexes of soluble solids,titratable acid,reactive oxygen in flesh and antioxidant enzyme activity of these two treatments were measured and compared at different time after flowering.The re-sults showed that in both years,enhanced UV-B radiation treatment inhibited soluble sugar accumulation and slowed down the decline of titratable acid content during the later stages of the treatment,leading to a signifi-cant decrease in the sugar-to-acid ratio and a decline in the overall nutritive and flavor quality of the fruit in rip-ening stage.The relative electrical conductivity and malondialdehyde(MDA)content of the fruit pulp under the enhanced UV-B radiation treatment were significantly higher than that of control.The H2O2 and O2-accu-mulated rapidly during the later stages of the enhanced UV-B radiation treatment and were significantly higher than that of control,and the hydroxyl radical scavenging rate was significantly lower than that of control in the later stages of the enhanced UV-B radiation treatment.The activities of peroxidase(POD)and superoxide dis-mutase(SOD)showed an overall downward trend of increase during the enhanced UV-B radiation treatment.Catalase(CAT)activity was significantly higher than that of control in the later stages of the enhanced UV-B radiation treatment.In conclusion,the enhanced UV-B radiation treatment at 96 kJ·m-2·d-1 eliminated re-active oxygen species(ROS)by enhancing the activity of antioxidant defense enzymes in the early stages of fruit expansion,thereby alleviating the damage caused by enhanced UV-B radiation.However,in the later sta-ges of fruit expansion or ripening,the treatment inhibited the activity of antioxidant enzymes,leading to an ac-cumulation of active oxygen radicals in the fruit and oxidative damage,resulting in a decline in fruit quality.
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