Manganese Hyperaccumulators and their Hyperaccumulating and Tolerance Mechanisms: A Review of the Current State of Knowledge

Manganese (Mn) is ubiquitous in the environment due to both geological and human activities. It is essential for plants, as for most other living organisms, but can also be toxic when it is present in excess. Some plant species, referred to as Mn hyperaccumulators, can accumulate over 10000μg/g of Mn in their shoot tissues without showing any phytotoxicity. Approximately 24 Mn hyperaccumulators are currently known worldwide. However, ample data is available the Mn hyperaccumulator species and biological significance of Mn hyperaccumulation and tolerance mechanisms. To give new insights, this review highlights the current knowledge of Mn hyperaccumulation and tolerance mechanisms in hyperaccumulators, which include root uptake, xylem loading, transport, sequestration, and detoxification processes. Hyperaccumulators uptake Mn mainly accumulates as Mn2+ into the xylem, from which it is then transferred to the shoots. Foliar Mn2+ is mainly stored in vacuoles, the endoplasmic reticulum, and the Golgi. It is sequestered by organic ligands and some transporter proteins at a subcellular level in the root and shoot, which can allow the plants to exhibit great tolerance. From the in-depth examine the published literature; the main knowledge gap and future research are highlighted. In addition, Mn hyperaccumulator biomass disposal methods and applications also discussed.