That old idiom, “Too much of a good thing is bad”, is well tailored to the topic being discussed. Consider this, Love of chocolates tends to be universal, tales of how dark chocolate helps with reducing cholesterol levels and acts as a natural antidepressant among others is well heard of. Yet we have been told from young on how consuming chocolates in excess leads to numerous ill effects, including high blood pressure, weight gain, etc. In other words, it is toxic in large quantity. So there’s a fine balance to be maintained between too much and too little.
Plants work quite the same way. In fact, the whole world works on careful balance and every living being in this same world must obey the law of balance. The seven essential micronutrients have to be maintained in a careful proportion or in other words the fine balance.From this, a careful conclusion can be drawn that too much leads to toxicity while too little gives rise to deficiency, which has been discussed earlier.
Mineral elements hold diverse functions in all plants including electron carriers, enzyme activation, providing osmoticum for turgor and growth, maintaining charge balance, structural components and etc.
The effects of mineral nutrient deficiencies in plants result in roots and leaf cessation, reduced growth, massive disruption in cell and cell walls, reduced branching, small changes in the pH of the cytosol, an inability of an enzyme to align correctly with a reactant, stunting, abnormal thickening, and darkening of roots. iron chlorosis, oxidative stress, chlorosis, destruction of chloroplasts, and death of cells and tissue due to the deficiencies of mineral nutrient.
This raises the question, how is this fine balance or careful proportion determined? There lies a very simple answer for this, the concentration of the mineral ion in tissue decrease the dry weight of tissues by 10 percent is said to be toxic. These concentrations do vary among different plants. Since every plant has different nutritional needs, varying weights, energy requirements and so on.
Also, another issue to be considered is that an excess intake of one element inhibits the uptake of another element. For instance, the presence of manganese toxicity is observed by the appearance of brown spots encompassed by chlorotic veins. Here the manganese competes with magnesium and iron for absorption and also hinders calcium translocation in the shoot apex of the plant. Consequently, the abundance of manganese in plants induces a deficiency of iron, copper, and calcium. So it is apparent that toxicity and deficiency are closely interlinked.
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