Abstract
Alternative oxidase (AOX) has been documented to mitigate the oxidative stress caused by abiotic stresses. However, it remains unknown how AOX regulates the antioxidant system and photosynthesis under waterlogging. To address this issue, we used two watermelon (Citrullus lanatus L.) cultivars (waterlogging tolerant cultivar ‘YL’ and sensitive cultivar ‘Zaojia8424’) as materials and the AOX inhibitor salicylhydroxamic acid (SHAM) to investigate the effects of AOX on photosynthesis and reactive oxygen species metabolism under waterlogging. We found that waterlogging decreased leaf photosynthesis and quantum yield of photosynthesis in watermelon, and the waterlogging tolerant cultivar ‘YL’ showed higher expression level of ClaAOX than the sensitive cultivar ‘Zaojia8424’. Net photosynthesis rate was higher in ‘YL’ than ‘Zaojia8424’. Moreover, waterlogging induced photoinhibition in ‘Zaojia8424’ but not in ‘YL’. Meanwhile, waterlogging promoted the accumulation of superoxide and peroxide hydrogen, and triggered oxidative damage. ‘YL’ suffered from less severe oxidative damage due to increased contents of ascorbate, a higher ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), a higher activity of ascorbate peroxidase (APX) and catalase (CAT), and enhanced levels of CAT and APX expression, relative to ‘Zaojia8424’. However, the alleviation of photosynthesis and oxidative damage, increased content of ascorbate and higher GSH/GSSG ratio were abolished by SHAM. Our results suggested that photosynthetic electronic transfer and glutathione-ascorbate cycle are involved in waterlogging tolerance mediated by the AOX pathway in watermelon.
Highlights
Introduction iationsWaterlogging is an emerging environmental factor restricting plant productivity due to climate change and influences almost 16% of global cultivated areas [1]
Results from gene expression analysis showed that waterlogging upregulated the expression of ClaAOX in both cultivars, with the tolerant cultivar ‘YL’
20 in Figure 5 showed that O2 and H2O2 contents a increased during waterlogging in both cultivars, with b less profound increases in O2− and b
Summary
Introduction iationsWaterlogging is an emerging environmental factor restricting plant productivity due to climate change and influences almost 16% of global cultivated areas [1]. Waterlogging initiates O2 deprivation within the roots, and triggers molecular, biochemical and physiological changes in both shoots and roots [1,3,4,5,6]. The reduction of net photosynthesis rate (Pn) by waterlogging has been observed in many plants, including cucumber (Cucumis sativus) [7], maize (Zea mays) [8], peanut (Arachis hypogaea) [9], sorghum (Sorghum bicolor) [10] and tomato (Solanum lycopersicum) [11].
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