Abstract
With the aim to clarifying the role of the ABA/H2O2 signaling cascade in the regulating the antioxidant capacity of grafted cucumber plants in response to Ca(NO3)2 stress, we investigated the relationship between ABA-mediated H2O2 production and the activities of antioxidant enzymes in the leaves of pumpkin-grafted cucumber seedlings. The results showed that both ABA and H2O2 were detected in pumpkin-grafted cucumber seedlings in response to Ca(NO3)2 treatment within 0.5 h in the leaves and peaked at 3 and 6 h after Ca(NO3)2 treatment, respectively, compared to the levels under control conditions. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POD) in pumpkin-grafted cucumber leaves gradually increased over time and peaked at 12 h of Ca(NO3)2 stress. Furthermore, in the leaves of pumpkin-grafted cucumber seedlings, the H2O2 generation, the antioxidant enzyme activities and the expression of SOD, POD and cAPX were strongly blocked by an inhibitor of ABA under Ca(NO3)2 stress, but this effect was eliminated by the addition of exogenous ABA. Moreover, the activities and gene expressions of these antioxidant enzymes in pumpkin-grafted leaves were almost inhibited under Ca(NO3)2 stress by pretreatment with ROS scavengers. These results suggest that the pumpkin grafting-induced ABA accumulation mediated H2O2 generation, resulting in the induction of antioxidant defense systems in leaves exposed to Ca(NO3)2 stress in the ABA/H2O2 signaling pathway.
Highlights
Greenhouse cultivation is the most common method of vegetable production worldwide
The abscisic acid (ABA) content in the leaves of pumpkin-grafted cucumber seedlings increased after 0.5 h of Ca(NO3)2 stress and peaked at 3 h
The H2O2 content in the leaves of pumpkin-grafted and self-grafted cucumber seedlings increased by Ca(NO3)2 stress compared to the corresponding controls (Figure 2)
Summary
Greenhouse cultivation is the most common method of vegetable production worldwide. secondary soil salinization in greenhouse soil, which is primarily caused by over-irrigation, intensive farming, lack of rain, and excessive application of nitrogenous fertilizers, restricts the development and productivity of vegetables in China (Blanco and Folegatti, 2002; Liang et al, 2005; Abbreviations: ABA, abscisic acid; APX, ascorbate peroxidase; CAT, catalase; DMTU, dimethylthiourea; DPI, diphenyleneiodonium chloride; POD, peroxidase; SOD, superoxide dismutase; Tiron, 1,2-dihydroxybenzene- 3,5disulphonic acid.ABA/H2O2 Signaling PathwayYu et al, 2005; He et al, 2007; Daliakopoulos et al, 2016). Greenhouse cultivation is the most common method of vegetable production worldwide. Secondary soil salinization in greenhouse soil, which is primarily caused by over-irrigation, intensive farming, lack of rain, and excessive application of nitrogenous fertilizers, restricts the development and productivity of vegetables in China Excessive Ca(NO3) leads to osmotic stress, inhibits biological nitrogen fixation, and modifies microbial soil biodiversity and causes the formation of reactive oxygen species (ROS) in plants. ROS can disorder the normal physiological metabolism and inhibit plant growth and decrease crop yield (Sainju et al, 2001). Plants have evolved adaptive protection mechanisms, such as antioxidant enzymes to protect themselves against the deleterious effects of ROS
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