Abstract Selenium (Se) is yet to be confirmed as essential for plants, but it has proven to be an essential trace element for humans and other animals. However, it is well documented that Se is a beneficial element for plants. Recent studies show that Se treatment at a low concentration exerts positive effects on plant growth, development, and yield. Thus, Se may act as a vital element by altering several physiological and biochemical processes. Remarkably, Se also acts as a plant antioxidant and pro-oxidant, and confers tolerance against different abiotic stresses, including salinity, drought, extreme temperature, and toxic metals/metalloids stresses. Its protective mechanism involves the enhancement of photosynthetic pigment synthesis, photosynthetic rate, gas exchange, accumulation of osmoprotectants, and secondary metabolites. Another important role of Se is the enhancement of the antioxidant defense system, which reduces reactive oxygen species (ROS) accumulation and thus oxidative stress. Moreover, Se also induces and modulates stress-responsive proteins/genes. Notably, an excessive Se concentration in growing media shows phytotoxicity associated with the overproduction of ROS as pro-oxidative Se activity, inhibition of the biosynthesis of photosynthetic pigments, and suppression of growth, developmental, and physiological processes. On the other hand, as a phytofortifier, Se may improve the nutritional quality of food crops and fodder. Moreover, plants can play important roles in overwhelming the Se deficiency and toxicity in various areas of the world; thus, a comprehensive mechanism of Se metabolism is crucial for effective Se-biofortification. Therefore, this review focuses on the recent advancement in the beneficial and harmful physiological role of Se in plants under abiotic stresses.

中文翻译：

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植物中的硒：恩还是祸？

摘要 硒（Se）尚未被确认为植物必需元素，但已被证明是人类和其他动物必需的微量元素。然而，据充分证明，硒是一种对植物有益的元素。最近的研究表明，低浓度硒处理对植物生长、发育和产量产生积极影响。因此，Se 可以通过改变几个生理和生化过程作为一种重要元素。值得注意的是，硒还充当植物抗氧化剂和促氧化剂，并赋予对不同非生物胁迫的耐受性，包括盐度、干旱、极端温度和有毒金属/类金属胁迫。其保护机制涉及增强光合色素合成、光合速率、气体交换、渗透保护剂的积累和次生代谢产物。硒的另一个重要作用是增强抗氧化防御系统，从而减少活性氧 (ROS) 的积累，从而减少氧化应激。此外，硒还诱导和调节应激反应蛋白/基因。值得注意的是，生长培养基中过量的硒浓度显示出与作为促氧化硒活性的 ROS 过量产生、抑制光合色素的生物合成以及抑制生长、发育和生理过程相关的植物毒性。另一方面，作为植物强化剂，硒可以改善粮食作物和饲料的营养品质。此外，植物可以在克服世界各个地区的硒缺乏和毒性方面发挥重要作用；因此，硒代谢的综合机制对于有效的硒生物强化至关重要。所以，