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. 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. 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.

中文翻译：

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硼毒性对野薄荷和弯腰柏生长，氧化损伤，抗氧化酶和精油指纹图谱的影响

硼（B）是必需的微量营养素，是植物正常生长所必需的。土壤和植物中B的浓度对生长和生产力至关重要。即使在土壤中可用的微量硼，硼对植物的毒性也极高，尤其是在半干旱和干旱环境中。在本研究中，阐明了高B浓度（2.5、5、10、20和30 mg / kg）对两种重要的含油植物的影响。薄荷脑和弯腰柏（Cymbopogon flexuosus）是具有众所周知的药用价值的芳香和抗菌药草。施用不同浓度的B对植物的生长具有抑制作用，从所研究植物的枝条和根长，枝干的鲜重和干重可以看出。B处理也降低了总叶绿素和类胡萝卜素含量，叶绿素荧光降低了碳酸酐酶和硝酸还原酶的活性。而且，与对照相比，B胁迫显着增加了脯氨酸含量和脂质过氧化物含量。在B胁迫下，过氧化氢酶，过氧化物酶和超氧化物歧化酶等抗氧化酶的活性也显着增加。B. 2.5 mg / kg B. arvensis和C. flexuosus的精油含量增加，并且随着B浓度的进一步增加而降低。目前的研究结果表明，B浓度的增加会抑制生长和光合色素，增加氧化抗氧化酶的破坏和活性；然而，轻度的B胁迫增加了M. arvensis和C. flexuosus植物的精油产量。