`star` Deficiency Symptoms of Essential Elements
`star` Toxicity of Micronutrients


● Whenever the `color{violet}"supply"`of an `color{Brown}"essential element"` becomes `color{violet}"limited"`, `color{Brown}"plant growth is retarded"`.

● The `color{violet}"concentration of the essential"` element below which plant growth is retarded is termed as `color{Brown}"Critical Concentration"`.

● The element is said to be `color{Brown}"deficient"` when present `color{violet}"below the critical concentration"`.

● Since each element has one or more specific `color{violet}"structural or functional role"` in plants, in the absence of any particular element, plants show `color{violet}"certain morphological changes"`.

● These `color{violet}"morphological changes"` are indicative of certain `color{violet}"element deficiencies"` and are called `color{Brown}"deficiency symptoms"`.

● The deficiency symptoms `color{violet}"vary from element to element"` and they disappear when the deficient `color{violet}"mineral nutrient is provided"` to the plant.

● However, if `color{violet}"deprivation continues"`, it may eventually lead to the `color{violet}"death of the plant"`.

● The parts of the plants that show the `color{violet}"deficiency symptoms"` also depend on the `color{violet}"mobility of the element"` in the plant.

● For elements that are `color{Brown}"actively mobilized"` within the plants and exported to young developing tissues, the deficiency symptoms tend to appear `color{violet}"first in the older tissues"`.

● For example, the deficiency symptoms of `color{Brown}"nitrogen, potassium"` and `color{Brown}"magnesium"` are visible first in the `color{violet}"senescent leaves"`.

● In the `color{violet}"older leaves"`, biomolecules containing these elements are `color{violet}"broken down"`, making these elements `color{violet}"available for mobilising"` to younger leaves.

● The deficiency symptoms tend to `color{violet}"appear first"` in the `color{violet}"young tissues"` whenever the elements are `color{Brown}"relatively immobile"` and are not transported out of the `color{violet}"mature organs"`, for example, elements like `color{Brown}"sulphur and calcium"` are a part of the `color{violet}"structural component"` of the cell and hence are not easily released.

● This aspect of `color{violet}"mineral nutrition"` of plants is of a great significance and importance to `color{violet}"agriculture and horticulture"`.

● The kind of `color{Brown}"deficiency symptoms"` shown in plants include `color{violet}"chlorosis, necrosis, stunted plant"` `color{violet}"growth, premature fall"` `color{violet}"of leaves and buds"`, and `color{violet}"inhibition of cell division"`.

● `color{Brown}"Chlorosis"` is the `color{violet}"loss of chlorophyll"` leading to `color{violet}"yellowing in leaves"`.

● This symptom is caused by the `color{violet}"deficiency of elements"` `color{Brown}"N, K, Mg, S"`, `color{Brown}"Fe, Mn, Zn"` and `color{Brown}"Mo"`.

● Likewise, `color{Brown}"necrosis"`, or `color{brown"death of tissue"`, particularly leaf tissue, is due to the deficiency of `color{violet}"Ca, Mg, Cu, K"`.

● Lack or low level of `color{Brown}"N, K, S, Mo"` causes an `color{violet}"inhibition of cell division"`.

● Some elements like `color{Brown}"N, S, Mo"` `color{Violet}"delay flowering"` if their concentration in plants is low.

● Thus the `color{Violet}"deficiency"` of any element can cause `color{Violet}"multiple symptoms"` and that the same symptoms may be caused by the deficiency of one of `color{Violet}"several different elements"`.

● Hence, to identify the `color{Violet}"deficient element"`, one has to study all the `color{Violet}"symptoms developed"` in all the various parts of the plant and compare them with the `color{Violet}"available standard tables"`.

● We must also be aware that `color{Violet}"different plants"` also respond differently to the `color{Violet}"deficiency of the"` `color{Violet}"same element."`


● The `color{Violet}"requirement of micronutrients"` is always in low amounts while their `color{Violet}"moderate decrease"` causes the `color{Brown}"deficiency symptoms"` and a `color{Violet}"moderate increase"` causes `color{Brown}"toxicity"`.

● In other words, there is a `color{Violet}"narrow range of concentration"` at which the elements are `color{Violet}"optimum"`.

● Any `color{Violet}"mineral ion concentration"` in tissues that `color{Violet}"reduces the dry weight"` of tissues by about `color{Violet}"10 per cent"` is considered `color{Violet}"toxic"`.

● Such `color{Violet}"critical concentrations"` vary widely among different micronutrients.

● The `color{Violet}"toxicity symptoms are difficult"` to identify.

● `color{Violet}"Toxicity levels"` for any element also `color{Violet}"vary"` for different plants.

● Many a times, `color{Violet}"excess of an element"` may inhibit the uptake of another element.

● For example, the prominent symptom of `color{Brown}"manganese toxicity"` is the appearance of `color{Violet}"brown spots"` surrounded by `color{Violet}"chlorotic veins"`.

● It is important to know that `color{Violet}"manganese competes"` with `color{Violet}"iron and magnesium"` for uptake and with magnesium for binding with enzymes.

● Manganese also `color{Violet}"inhibit calcium translocation"` in shoot apex.

● Therefore, `color{Violet}"excess of manganese"` may, in fact, induce deficiencies of `color{Brown}"iron, magnesium and calcium"`.

● Thus, what appears as symptoms of `color{Violet}"manganese toxicity"` may actually be the deficiency symptoms of `color{Violet}"iron, magnesium and calcium"`.