Effects of boron toxicity on growth, oxidative damage, antioxidant enzymes and essential oil fingerprinting in Mentha arvensis and Cymbopogon flexuosus

Background Boron (B) is an essential micronutrient and necessary to plants for their proper growth. The concentration of B in soil and plant is greatly critical for the growth and productivity. Even at the low amount available in soils, B can be extremely toxic to plants especially in semi-arid and arid environments. In the present study, the effects of high B concentrations (2.5, 5, 10, 20 and 30 mg/kg) were elucidated on two important essential oil-bearing plants; Mentha arvensis and Cymbopogon flexuosus which are aromatic and antimicrobial herbs having well-known medicinal values. Results Application of different concentrations of B showed growth inhibitory effects on plant as evident by shoot and root lengths, fresh and dry weights of shoot in the studied plants. Treatments of B also reduced the total chlorophyll and carotenoid content, chlorophyll fluorescence and reduced the activities of carbonic anhydrase and nitrate reductase enzymes. Moreover, B stress considerably increased the proline content and lipid peroxide content as compared to control. The activities of antioxidant enzymes like catalase, peroxidase and superoxide dismutase were also significantly increased under B stress. The content of essential oil of M. arvensis and C. flexuosus increased at 2.5 mg/kg of B and decreased with further increase in concentrations of B. Conclusion The findings of present work suggest that increasing concentrations of B inhibited growth and photosynthetic pigments, increased oxidative damage and activities of antioxidant enzymes; however, a mild stress of B increased essential oil production in M. arvensis and C. flexuosus plants.