Coupon Accepted Successfully!


Role of Macro and Micronutrients

The essential elements perform several roles. The most important role of the elements is to participate in various metabolic activities of the plant. For example, some elements regulate the permeability of cell membranes, some are required for the maintenance of osmotic pressure of cell sap, and others participate in an electron transport system, buffer action, electrical neutrality, etc. The role and symptoms of their deficiency in plants are discussed below.

The role of individual elements has been largely determined by growing plants with their roots immersed in nutrient solution without soil. This technique is known as hydroponics. Usually, a large volume of nutrient solution is required for hydroponic culture, and the concentration of nutrients is adjusted frequently to prevent changes in nutrient concentration and pH of the medium. Vigorous bubbling of the air through the medium is also routinely done to provide sufficient oxygen to the root system. For studying deficiency symptoms, the particular ion is eliminated from the nutrient medium. Hydroponics, or water culture, has found wide application in growing many crops under artificial conditions for economic purposes as well.

Different types of minerals often influence different aspects of plant life. It is not possible, thus, to generalise the functions of all the minerals, hence we will deal with them individually.You already know that carbon, hydrogen and oxygen are the building blocks of macromolecules. Now, you will study about other elements.


This is the mineral element required by plants in greatest amount. It is absorbed as NO2-, NO3- or NH4+. This is required by all parts of a plant, particularly the meristematic tissues. Nitrogen is one of the major constituents of proteins, nucleic acids, vitamins and hormones. Its deficiency causes yellowing or leaves growing older (chlorosis), stunting of plants, dormancy of lateral buds, late flowering, purple colouration in shoot axis surface, wrinkling of cereal grains, and inhibition of cell division.


Phosphorus is found in plants as a constituent of nucleic acids, phospholipids, coenzymes NAD and NADP and most important, as a constituent of ATP. High concentration of phosphate is found in the meristematic tissues of actively growing plants, where it is involved in nucleo-protein synthesis. Phosphorus is also involved through the ATP molecule, in the activation of amino acids, for the synthesis of proteins. Phospholipids form important structural and functional molecules of the cell membranes. The coenzymes NAD and NADP which take part in oxidation-reduction reactions are important constituents for cellular metabolism. Such important processes as photosynthesis, glycolysis, respiration and fatty acid synthesis depend on these coenzymes. The ATP molecule is important for energy storage and transfer.
Phosphorus deficiency may cause premature leaf fall, and purple of red anthocyanin pigmentation. Plants lacking phosphorus may develop dead, necrotic (degenerative) areas on leaves, petioles or fruits; they may have an overall stunted appearance. Phosphorus deficiency has been shown to interfere with the proper development of vascular tissues, xylem and phloem, in plants. Deficiency of this element has been shown to cause an accumulation of carbohydrates in certain plants such as sunflower, soyabean and black mustard.


Potassium deficiency may affect processes such as photosynthesis, chlorophyll development, respiration and retention of water by leaves. However, the specific function of potassium in the life of plants is poorly understood. The meristematic tissues of plants contain very high levels of potassium and it is essential as an activator of enzymes involved in the synthesis of certain peptide bonds. Potassium is also believed to act as an activator for several enzymes involved in carbohydrate metabolism.

Potassium deficiency is easily recognised on the leaves of the plant. First a mottled chlorosis occurs, then necrotic areas develop at the tip and margins of the leaf. In many cases leaves of the potassium deficient plants show a tendency to curve downward. Potassium deficiency in tomato plants causes disintegration of pith cells and results in an increase in the differentiation of secondary phloem parenchyma into sieve tubes and companion cells.


The most important function of sulphur, possibly, is its participation in protein structure, in the form of sulphur containing amino acids (cystine, cysteine and methionine). The vitamins biotin, thiamine and coenzyme A contain sulphur. The sulphydryl groups (-SH) present in many enzymes are necessary for their enzymic activity. Sulphur also plays an important part in stabilising the protein structure through sulphur cross links in the protein molecule.

A general chlorosis followed by the production of anthocyanin pigments in leaves are visible symptoms of sulphur deficiency. Under severe sulphur deficiency conditions all of the leaves of the plants may undergo some loss of green colour. Sulphur deficiency also causes the accumulation of starch, sucrose and soluble nitrogen as has been shown in sulphur deficient tomato, sunflower, black mustard and soyabean.


One of the well-known functions of calcium in plant tissues is its role as a constituent of cell walls in the form of calcium pectate. The middle lamella of plant cell walls is composed of calcium and magnesium pectate. In plant cells calcium may be important for the formation of cell membranes and lipid structures. Calcium in small amounts has been shown to be necessary for normal mitosis. It has been suggested that calcium maybe an activator of several enzymes, such as arginine kinase, adenosine triphosphatase, adenyl kinase and potato apyrase. Calcium deficiency often results in reduction in the number of mitochondria in wheat roots.

Calcium deficiency affects the meristematic regions of stems, leaf and root tips which eventually die resulting in termination of growth in these regions. Roots may become short, stubby and brown as in calcium deficient tomato plants. One of the characteristic features of calcium deficient plants is that their younger leaves show malformation and distortion. Cell walls may become rigid or brittle in calcium deficient plants. Vacuolization of cells occurring closer to the root apex, cell enlargement, vacuolization and differentiation occurring closer to the shoot apex are all characteristics of calcium deficiency in plants.


In plants magnesium is important for photosynthesis and carbohydrate metabolism. Magnesium is a constituent of the chlorophyll molecule without which photosynthesis would not occur. Many of the enzymes involved in carbohydrate metabolism require magnesium as an activator. The enzymes involved in the synthesis of the nucleic acids also need magnesium as an activator. It has been suggested that magnesium maya have two roles in protein synthesis; (1) as an activator in some of the enzyme systems involved in the synthesis of nucleic acids; (2) as an important binding agent in microsomal particles where photosynthesis takes place in the cell.

The most common symptom of magnesium deficiency in green plants is extensive interveinal chlorosis of the leaves. Chlorosis is often followed by the appearance of anthocyanin pigments in the leaves. Following chlorosis and pigmentation, necrotic spotting may be observed.


Iron has been shown to be essential for the synthesis of chlorophyll. It has also been identified as a component of various flavoproteins active in biological oxidations. Iron is also found in the iron porphyrins, such as cytochrome. The most easily observed symptom of iron deficiency in plants is extensive chlorosis in the leaves.


Manganese is an essential factor in respiration and nitrogen metabolism. In both these cases it functions as an enzyme activator. Manganese plays an important role in nitrate reduction; manganese acts as an activator for the enzyme, nitrite reductase. Manganese is also important for photosynthesis. At an early stage of manganese deficiency, the rate of photosynthesis in algae shows a decrease. Manganese deficiency is characterised by the appearance of chlorotic and necrotic spots in the interveinal areas of the leaf.


The function of boron is not understood clearly. Many functions have been suggested for boron in plant metabolism. However, its function in the translocation of sugar is the only generally accepted one. Boron has been implicated in cellular differentiation, nitrogen metabolism, fertilisation, active salt absorption, hormone metabolism, water relations, fat metabolism, photosynthesis etc. It could be possible that the role of boron in all these processes may be indirect and related to its primary functions of translocations of sugar. The first visible symptom of boron deficiency is the death of the shoot tip. This usually causes the growth of lateral shoots, the tips of which also eventually die. Generally flowers do not form in boron deficient plants and root growth is stunted.


Zinc is involved in biosynthesis of plant auxin, indole-3-acetic acid (IAA). Zinc participates in the metabolism of plants as an activator of several enzymes.

Generally the first sign of zinc deficiency is an interveinal chlorosis of older leaves starting at the tips and margins. Smaller leaves, shortened internodes and stunted growth are characteristics of zinc deficiency.


Copper acts as a component of phenolases, lactase, and ascorbic acid oxidase, and its role as a part of these enzymes is, probably, the most important function of copper in plants. It has also been demonstrated that copper, in some way, influences photosynthesis, possibly through influencing carbon dioxide absorption.

Copper deficiency generally causes necrosis of the tip of young leaves that proceeds along the margin of the leaf, giving it a withered appearance.


Molybdenum is well known to influence nitrogen fixation and nitrate assimilation. Apart from its role in nitrogen metabolism it seems to be necessary to keep the ascorbic acid concentration in plants. Molybdenum deficiency leads to a drop in the concentration of ascorbic acid in plants. Normal levels of ascorbic acid are restored on addition of molybdenum. It has been suggested that ascorbic acid may have a protective role in the chloroplast.

Visible signs of molybdenum deficiency may start with chlorotic interveinal mottling of the lower leaves. Molybdenum deficiency leads to inhibition of flower formation and even if flowers are formed they abscise before setting fruit.

Other elements

Apart from the elements described above, many plants may require several other elements for their normal growth and development. Sodium, for example, may be necessary for the growth of some marine algae. Normal growth and development of several blue-green algae depends on the availability of sodium. Silicon has been shown to improve growth of barley and sunflower plants. The growth of rice and millet also improves when silicon is added to the culture medium. Several algae contain silicified structures; silicon is considered essential for these plants. Chlorine is an essential element in some plants. Chlorine influences the process of photosynthesis and also helps in the maintenance of ionic balance.

The mineral elements required by higher plants, their source, form of absorption and major functions are summarized in the table below:

Elements required by higher plants




Form of absorption

Major functions

1.Non-Mineral Elements

Carbon ( C )



Constituent of organic molecules

Oxygen (O)



Constituent of most organic molecules

Hydrogen (H)



Constituent of most organic molecules

Nitrogen (N)


NH4+ & NO3-

In proteins, nucleic acids, etc.

2.Mineral Nutrients

(a) Macronutrients

Phosphorus (P)



In nucleic acids; ATP, phospholipids, etc.

Potassium (K)



Enzyme activation, water balance, etc.

Sulphur (S)



In proteins, coenzymes

Calcium (Ca)



Affects cell walls, membranes and many enzymes

Magnesium (Mg)



In chlorophyll required by many enzymes, stabilizes ribosomes

(b) Micronutrients

Iron (Fe)



In active sites of many redox enzymes and electron transport carriers; needed for chlorophyll synthesis

Chlorine (Cl)



Involved in photosynthesis and in ionic balance

Manganese (Mn)



Activates many enzymes

Boron (B)


H2BO3-, HBO32-

Perhaps involved in carbohydrate transport

Zinc (Zn)



Activates some enzymes; needed for auxin synthesis

Copper (Cu)



In active sites of many redox enzymes and electron carriers

Molybdenum (Mo)



Nitrogen fixation; nitrate reduction

Test Your Skills Now!
Take a Quiz now
Reviewer Name