Aluminum (Al) toxicity is a major limiting factor for plant productivity. Boron (B) could mitigate Al toxicity in many plant species. However, information about the mechanisms of B alleviating Al toxicity in citrus is lacking. Trifoliate orange rootstock (Poncirus trifoliate L. Raf.) seedlings were irrigated with a nutrient solution containing two B and two Al levels. Results showed that exposure to Al severely impeded plant growth-related parameters. However, B supply improved plant biomass, root activity and relative root elongation under Al stress. Furthermore, B reduced the Al-induced H2O2 accumulation in roots as evidenced by lower fluorescence intensity of H2O2 staining. Boron decreased the Al-stimulated ascorbate (AsA) synthesis by down-regulated AsA synthesis-related metabolites in the L-galactose pathway. Boron alleviated some of the toxic effects of Al by decreasing redox states of AsA and enzyme activities involved in ascorbate-glutathione (AsA-GSH) cycle, ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase and glutathione peroxidase while increased glutathione (GSH) content and γ-glutamylcysteine synthetase (γ-GCS) activity. Overall, our results suggest that B protects roots against Al-induced oxidative stress possibly by reducing metabolites accumulation in the L-galactose pathway of AsA synthesis and regulating AsA-GSH cycle.
Keywords: Aluminum toxicity; AsA-GSH cycle; Boron; L-galactose pathway; Trifoliate orange rootstock.
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