EFFECT OF EXOGENOUS SUBSTANCE PRETREATMENT ON ANTIOXIDATIVE ABILITY OF PEAR FRUITS UNDER HIGH TEMPERATURE AND EXCESSIVE SUNLIGHT STRESS

In the present experiment, the effect of exogenous substance pretreatment with AsA, oxalic acid, SA and ABA on dynamic changes of antioxidative enzymes and antioxidants in the AsA-GSH cycle of ‘Yali’ fruits was investigated under high temperature and excessive sunlight stress. The results indicated that, the AOS (activated oxygen species) content with the control increased significantly under the stress of both high temperature and excessive sunlight. In the initial stress stage, the pretreatment with different exogenous antioxidants could consistently raise total AsA and reduced AsA contents and GR activity and thus in the later stress stage, the AOS contents were significantly lower than those with the control. Although total AsA and reduced AsA contents as well as GR activity in fruits pretreated with antioxidants showed also a decreasing trend during stress treatment, their antioxidative levels were still significantly higher than the control. In the initial phase subjected to high temperature and excessive sunlight, no significant effect was found on APX activity and AsA/DHA ratio in fruits among various treatments but thereafter, the APX activity and AsA/DHA ratio with exogenous antioxidant pretreatment were enhanced significantly, compared to the control, implying that APX actively participated in scavenging AOS free radicals. It is concluded that exogenous antioxidant pretreatment could improve the antioxidative ability in pear fruits and thus raise the resistance to high temperature and excessive sunlight stress.