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The Role of Siderophores on Plants under Heavy Meal Stress: A View from the Rhizosphere

Mihiri Seneviratne and Meththika Vithanage

Siderophores are Fe chelators produced by both microbes and plants. Since Fe is an essential element to all forms of life, siderophores plays a vital role to overcome the Fe limitations. It has been revealed that in the rhizosphere, where many complex biochemical reactions takes place, both microbial and plant siderophores involve to fulfill Fe requirements of the plant. Interestingly, siderophores exhibit a tremendous role in protecting the plant from oxidative stress caused by heavy metals. Even though they have the ability to bind trace metals and toxic heavy metals; the affinity towards them is somewhat low. Even though siderophores form complexes with heavy metals, unlike Fe it restrains they deliver through the plasma membrane of the root cells. Thereby siderophores reduce the metal accumulation in the plant. However, conflicting results are observed in different studies. Under some plant siderophore combinations, plant heavy metal uptake exhibited an increase, which shows its favorability to enhance phytoremedation. Furthermore, siderophores are able to reduce the oxidative stress by inhibiting the free radical formation and can inhibit the IAA destruction. Collectively they are able to reduce the plant stress factors and induce plant growth promotion. In this review, we have summarized the protective role of siderophores, their heavy uptake strategies, biosynthesis and the siderophore transport through the cell membrane. This is a novel field of research with numerous gaps are to be filled, which would light the pathway to understand the marvels of nature.