Mineral Toxicity

Several minerals cause specific problems once their concentration exceeds the adequate range. Manganese toxicity blocks the uptake of iron and magnesium and prevents calcium from being translocated to the shoot apex, so an excess of manganese produces deficiency-like symptoms of these other three minerals even though they are present in the soil; visibly, it appears as brown spots surrounded by chlorotic veins. Aluminium toxicity causes precipitation of nucleic acids, inhibits the enzyme ATPase, blocks cell division, and interferes with calmodulin binding to the plasma membrane. Iron and manganese show a competitive relationship with each other: because their deficiency symptoms look similar, and because iron toxicity specifically interferes with manganese absorption, an oversupply of chelated iron combined with increased soil acidity (pH below 5.8) is a common cause of iro …