Relationship between reactive oxygen species and ultraweak luminescence in strawberry fruit during senescence under various reactive oxygen regulation treatments

Abstract:【Objective】The relationship between ultraweak luminescence (UWL) and growth and develop⁃ment of plants is a new research topic and the mechanism of UWL generation in plants is completely un⁃known. To examine the hypothesis that reactive oxygen species is related with the generation of UWL inplants, we carried out the experiment of soaking‘Hongyan’strawberry fruit with hydrogen peroxide(H2O2) and tea polyphenol (TP) and analyzed variations in UWL and reactive oxygen species under varioustreatments during the senescence process of the fruit.【Methods】The plants of strawberry‘Hongyan’used in this study were planted in the greenhouses in Nongfeng Fruit and Vegetable Farm Cooperation inthe new urban district of Hohhot in September 2014. In April 2015, healthy mature fruit uniform in sizewere harvested and taken to lab immediately. The fruit were divided into 3 groups and were separatelysoaked for 30 minutes in 0.1 mmol·L^-1 H₂O₂, 100 mg·L^-1 TP, and distilled water (as control). After soak⁃ing, the fruit were air-dried, put into preservative bags and stored under normal temperature. During the 6 days of storage, fruit samples were taken for physical index measurements every day. Part of each fruitsample were measured immediately for UWL intensity with a BPCL-2-SH instrument produced by Bei⁃jing Jianxin Science and Technology Company. The measurement procedure was according to the instru⁃ment instruction. The average value of 10 measurements from 10 fruit of each sample was assigned as theUWL intensity of that sample. The remaining part of each fruit sample were frozen in liquid nitrogen andstored under -80 ℃ in a freezer for the analyses of the indexes of lipoxygenase (LOX) activity, superoxideanion radical（O2^-·）production rate, H2O2 content, malondialdehyde (MDA) content, and relative electricconductivity.【Results】During the senescence of fruit, the LOX activities in H2O2 treatment, TP treatmentand the control increased first and then decreased. O2 -·production rates, MDA content and relative electricconductivity in the three treatments increased continuously. UWL intensity in three treatments showed agradual declining trend. Based on the above results, during the senescence process of strawberry fruit, reactive oxygen species generated and accumulated constantly, and UWL intensity declined along with theaccumulation of reactive oxygen species. Meanwhile, throughout the process of senescence, the O2 -·production rate, MDA content and relative electric conductivity in H₂O₂ treatment were all higher but UWL inten⁃sity was lower than in the control. While the O2^-· production rate, MDA content and relative electric con⁃ductivity in TP treatment were all lower, the UWL intensity was higher than in the control. The above results suggested that increasing reactive oxygen species led to decline in UWL intensify in fruit, while scav⁃enging reactive oxygen species slowed the decline in UWL intensity. Correlation analysis between reactiveoxygen levels and UWL intensity in fruit showed that UWL intensity had a significant negative correlationwith O2 ^-·production rate, MDA content and relative electric conductivity in all treatments and that the neg⁃ative correlation between UWL intensity and reactive oxygen under H2O2 treatment was the most signifi⁃cant. The above correlation analyses further proved that reactive oxygen accumulation led to the decline inUWL intensity in fruit.【Conclusion】The radiant and active status formed from the interaction among re⁃active oxygen species has been suggested as the source of UWL. According to this suggestion, the accumu⁃lation of reactive oxygen species lead to enhanced UWL emission. The present study showed that UWL in⁃tensity declined with the accumulation of reactive oxygen species. Increasing reactive oxygen species infruit intensified the decline in UWL intensity, while eliminating reactive oxygen slowed the decline inUWL intensity in fruit, indicating that reactive oxygen species might not be the direct source of UWL butcan affect UWL by affecting other cellular metabolisms, which await further studies.