Mineral Nuritent One Shot
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Introduction
The basic needs of all living organisms are essentially the same. They require macro-molecules, such as
carbohydrates, proteins and fats and water and minerals for their growth and development.
Methods to study the mineral requirements of plants
History : In 1860, Julius Von Sachs, a prominent German Botanist, demonstrated, for the first time, that
plants could be grown to maturity in a defined nutrient solution in complete absence of soil.
"This technique of growing plants in a nutrient solution is known as hydroponics."
Aim of hydroponics : To determine the mineral nutrients essential for plants.
Requirements of hydroponics :
(i) Purified water
(ii) Mineral nutrient salts
(iii) The nutrient solution must be adequately aerated to obtain the optimum growth.
Essential Mineral Elements
· Most of the minerals present in soil can enter plants through roots.
· In fact, more than sixty elements of the total discovered so far are found in different plants.
· Some plant species accumulate selenium (Astragalus), some others gold, while some plants growing near
nuclear test sites take up radioactive strontium.
· There are techniques that are able to detect the minerals even at a very low concentration (10–8 g/mL).
Criteria for essentiality : The criteria for essentiality of an element are given below :
(a) The element must be absolutely necessary for supporting normal growth and reproduction. In the absence
of the element the plants do not complete their life cycle or set the seeds.
(b) The requirement of the element must be specific and not replaceable by another element. In other words,
deficiency of any one element can not be met by supplying some other element.
(c) The element must be directly involved in the metabolism of the plant.
Based upon the above criteria only 17 elements have been found to be absolutely essential for plant growth and
metabolism.
These elements are further divided into two broad categories based on their quantitative requirements.
(i) Macronutrients
(ii) Micronutrients
(i) Macronutrients :
· They are generally required in plants tissues in large amounts i.e. excess of 10 m mole kg–1 of dry matter.
· They are nine in number eg., carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium
and magnesium.
· Out of these carbon, hydrogen and oxygen are mainly obtained from CO2 and H2O, while the others are
absorbed from the soil as mineral nutrition.
(ii) Micronutrients or trace elements :
· They are needed in very small amounts i.e. less than 10 mmole Kg–1 of dry matter.
· They are eight in number. These include iron, manganese, copper, molybdenum, zinc, boron, chlorine and
nickel.
· Fe is required in large amounts in comparision to other micronutrients, while Mo is required in minimum
quantity.
· In addition to the 17 essential elements, there are some beneficial elements such as sodium (Atriplex),
silicon (grasses), cobalt (legumes) and selenium (Astragalus). They are required by higher plants.
Essential elements can also be grouped into four broad categories on the basis of their diverse functions.
These categories are :
(i) Essential elements that are components of biomolecules and hence structural elements of cells.
Examples : carbon, hydrogen, oxygen and nitrogen.
(ii) Essential elements that are components of energy-related chemical compounds in plants
Examples : Magnesium in chlorophyll and phosphorus in ATP.
(iii) Essential elements that activate enzymes, for example Mg2+ is an activator for both RuBisCO and
PEPcase, both of which are critical enzymes in photosynthetic carbon fixation; Zn2+ is an activator of
alcohol dehydrogenase and Mo of nitrogenase during nitrogen metabolism.
(iv) Some essential elements can alter the osmotic potential of a cell. Potassium plays an important
role in the opening and closing of stomata.
Deficiency symptoms of essential elements :
· The concentration of the essential elements, below which plant growth is retarded, is termed as critical
concentration.
· The essential element is said to be deficient when present below the critical concentration.
Prevalent deficiency symptoms in plants :
(i) Chlorosis : It is the loss of chlorophyll leading to yellowing in leaves. This symptom is caused by the deficiency
of elements N, K, Mg, S, Fe, Mn, Zn and Mo.
(ii) Necrosis : It is the death of tissue, particularly leaf tissue, is due to the deficiency of Ca, Mg, Cu and K.
(iii) Inhibition of cell division : Deficiency of N, K, S and Mo causes an inhibition of cell division.
(iv) Delay in flowering : Deficiency of N, S and Mo causes delay in flowering.
Therefor, the deficiency of any element can cause multiple deficiency symptoms and that the same deficiency
symptom may be caused by the deficiency of one of several different elements
Toxicity of micronutrients
· The requirement of micronutrients is always in low amounts, there is a narrow range of concentration at which
the micronutrients are optimum.
· Moderate decrease of micronutrient causes the deficiency symptoms and moderate increase causes toxicity.
· Any mineral ion concentration in tissues that reduces the dry weight of tissues by 10 percent is considered toxic.
· Toxic concentration is variable for the same micronutrient in different plants and also variable for different
micronutrients in same plant.
Example : Mn toxicity followed by apperance of brown spots surrounded by chlorotic veins.
Impacts of Mn toxicity :
(i) Manganese competes with iron and magnesium for uptake.
(ii) Manganese competes with magnesium for binding with enzymes.
(iii) Manganese inhibits calcium translocation in shoot apex.
Conclusion : Excess of manganese may, infact, induces deficiencies of iron, magnesium and calcium. Thus,
what appears as symptoms of manganese toxicity may actually be the deficiency symptoms of iron, magnesium
and calcium.
Uptake and transport of mineral nutrients
Plants obtain their carbon and most of their oxygen from CO2 in the atmosphere. However, their remaining
nutritional requirements are obtained from minerals and water for hydrogen in the soil.
Uptake of mineral ions :
All minerals can not be passively absorbed by the roots. Two factors account for this :
(i) Minerals are present in the soil as charged particles (ions) which can not move passively across cell membranes.
(ii) The concentration of minerals in the soil is usually lower than the concentration of minerals in the root.
· Therefore, most minerals must enter the root by active absorption into the cytoplasm of epidermal cells. Although
some ions also move into the epidermal cells passively.
· The active uptake of ions is partly responsible for the water potential gradient in roots and therefore for the
uptake of water by osmosis.
Studies on mechanism of absorption of elements revealed that the process of absorption can be demarcated
into two main phases :
(i) Initial phase (ii) Metabolic phase
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