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Mineral Nutrition:METHODS TO STUDY THE MINERAL REQUIREMENTS OF PLANTS:
Technique of growing plants in a nutrient solution in complete absence of soil is known as hydroponics. This method requires purified water and mineral nutrient salts. During hydroponics, a mineral solution suitable for the plant growth was obtained after a series of experiments in which the roots of the plants were immersed in nutrient solutions and wherein an element was added / removed or given in varied concentration. By this method, essential elements were identified and their deficiency symptoms discovered. The nutrient solutions must also be adequate aerated to obtain optimum growth. This is because aeration provides
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roots with O2 for cellular respiration. Plants cannot circulate nutrients as they lack a circulatory system, so roots must take up gases directly from soil or water. Diagrammatic views of the hydroponic technique is given in Figures 1.a and 1.b
Essential Mineral Elements:
Roots of plants take up different minerals present in the soil. For example, selenium, gold, and radioactive strontium are some minerals taken up by certain plants. However, for these mineral elements to be considered essential to the plants, they must satisfy some criteria.
Criteria for Essentiality:
The criteria for an element to be considered an essential element is 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 cannot be met by supplying some other element.
(c) The element must be directly involved in the metabolism of the plant.
The essential elements are further divided into two broad categories based on the quantitative requirements:
(i) Macronutrients, and
(ii) Micronutrients
(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 cannot be met by supplying some other element.
(c) The element must be directly involved in the metabolism of the plant.
The essential elements are further divided into two broad categories based on the quantitative requirements:
(i) Macronutrients, and
(ii) Micronutrients
In addition to the 17 essential elements named above, there are some beneficial elements such as sodium, silicon, cobalt and selenium. They are required by higher plants.
The 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 (e.g., carbon, hydrogen, oxygen and nitrogen).
(ii) Essential elements that are components of energy - related chemical compounds in plants (e.g., magnesium in chlorophyll and phosphorous in ATP).
(iii) Essential elements that activate or inhibit enzymes, for example Mg2+ is an activator for both ribulose bisphosphate carboxylase- oxygenase and phosphoenol pyruvate carboxylase, 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 that can alter the osmotic potential of a cell. Potassium plays an important role in the opening and closing of stomata. You may recall the role of minerals as solutes in determining the water potential of a cell.
The 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 (e.g., carbon, hydrogen, oxygen and nitrogen).
(ii) Essential elements that are components of energy - related chemical compounds in plants (e.g., magnesium in chlorophyll and phosphorous in ATP).
(iii) Essential elements that activate or inhibit enzymes, for example Mg2+ is an activator for both ribulose bisphosphate carboxylase- oxygenase and phosphoenol pyruvate carboxylase, 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 that can alter the osmotic potential of a cell. Potassium plays an important role in the opening and closing of stomata. You may recall the role of minerals as solutes in determining the water potential of a cell.
Role of Macro- and Micro-nutrients:
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