Plant Physiological Role and Deficiency Symptoms of Mineral Elements
These are not mineral elements in the true sense but have been included because these elements form the composition of all organic compounds present in plants. They are a part of carbohydrates, proteins, and fats. Thus these elements have a role to play in the general metabolism of plants.
Deficiency of these elements is very rare because the plants have a steady supply of these through water and gaseous exchange. Deficiency affects the normal growth and developments of plants.
Nitrogen is an essential constituent of proteins, nucleic acids, vitamins and many other organic molecules such as chlorophyII. Nitrogen also forms a constitutent of various hormones, coenzymes and ATP.
i) Stunted growth
iii) Reduction in flowering
iv) Excessive colouring in apple and peach and reduction in fruit size.
v) Decrease in protein contents
vi) Change in the pigmentation pattern
It is present in plasma membrane, nucleic acids, nucleotides, many co-enzymes and organic molecules. It plays an important role in energy metabolism. Phosphorus promotes healthy root growth and fruit ripening.
i. Loss of older leaves
ii. Reduction in growth
iii. Increase in phosphatase enzyme activity
iv. Causes accumulation of carbohydrates in soyabean
Potassium is required in the meristematic regions and regions of cell differentiation. It accumulates in older leaves. Though it does not have a structural role, it is involved in stomatal opening and closing. It is an activator of many enzymes and has a role in protein and carbohydrate metabolism.
i. Leaf tips curve downward
ii. Causes mottled chlorosis
iii. Development of chlorosis at tips and margins of leaves.
iv. Shortening of internodes and stunted growth.
Sulphur is the constituent of certain vitamins such as thiamine and biotin. It is constituent of coenzyme - A playing an important role in respiration. It forms the sulphydryI group in many enzymes and is a constitutent of sulphur containing aminoacids such acystine, cysteine and methionine.
i. Causes inhibition of protein synthesis.
ii. Younger leaves show chlorosis first
iii. Chloroplasts of mesophyII show a decrease in stroma lamellae but grana increase.
Magnesium is a constituent of chlorophyII molecule which cannot be formed without magnesium. It has a vital role in carbohydrate metabolism and the binding of ribosomal sub-units. Magnesium is the activator of many enzymes involved in DNA and RNA synthesis. It acts as a phophours carrier and activates enzymes such as PEP carboxylase and RuBP carboxylase.
i. Interveinal chlorosis takes place.
ii. Anthocyanin pigment deposition takes place after chlorosis.
iii. Necrotic spots appear in acute cases.
Calcium forms an important constituent of the cell wall occurring in the middle lamella as calcium pectate. It has an important role in the formation of plasma membrane. Calcium plays a role in mitotic cell division and is a constitutent of enzymes likephospholipase and adenyl kinase where it acts as an activator.
i. Affects the carbohydrate metabolism.
ii. The process of respiration is badly affected as number of mitochondria are decreased.
iii. Meristematic tissues are affected and leaf and root tips die.
iv. Cell wall may become brittle or rigid.
Soil is generally not deficient in iron. Iron is a constituent of various flavoproteins and forms a part of enzymes such as catalases, peroxidases and cytochromes. It plays an important role in the electron transport system of photosynthesis being part of cytochrome and ferredoxin.
i. Causes interveinal chlorosis and the leaves become yellow or white.
ii. Impairs aerobic respiration and related processes.
iii. Fruit trees particularly show sensitivity to iron deficiency.
Leaves and seeds require boron. It is necessary for uptake and utilisation of Ca++ ions, pollen germination, cell differentiation and translocation of carbohydrates. It plays a role in nitrogen metabolism, hormone and fat metabolism.
i. It causes brown heart-rot disease in beetroots.
ii. In apple internal tissues become corky.
iii. Causes leaf to curl and become brittle.
iv. Premature fall of fruits and flowers.
Managanese is required by leaves and seeds. It is an activator of enzymes like carboxylases, oxidases, dehydrogenses andkinases.
i. Causes grey spot disease in oat.
ii. Poor development of root system.
iii. Interveinal chlorosis occurs.
This is required in all plant parts. Copper forms a component of enzymes such as phenolases and tyrosinase. Copper being a constituent of plastocyanin plays a role in photophosphorylation. Copper maintains the carbohydrate - nitrogen balance.
i. Causes die back of shoots especially in Citrus.
ii. A disease called 'exanthema' causes the yield of gums on the bark.
iii. Reclamation disease is caused in plants growing on newly reclaimed soil where seed formation is affected.
Zinc is involved in the synthesis of indole acetic acid by activating the enzyme tryptophan synthetase. It plays a role in protein synthesis. It acts as an activator of many other enzymes such as carbonic anhydrase, alcohol dehydrogenase, hexokinase and so on.
i. Causes distortion of growth.
ii. Leaves become very small and rosetted called as little leaf disease.
iii. Interveinal chlorosis and stunted growth of stems is seen.
Molybdenum has an important role to play in the metabolism of nitrogen. It affects the synthesis of ascorbic acid. It activates the enzymes involved in nitrogen metabolism.
i. It leads to mottling and wilting of leaves at the margins causing 'yellow spot' disease of Citrus.
ii. 'Whiptail' disease in cauliflowers causing narrowing of leaf blades and their rugged appearance due to distortion.