Function and Deficiency symptoms of phosphorus and Abundant supply/overdose/toxicity
Function of phosphorus
i. Phosphorus plays a vital role as a structural component of cell. It is a constituents and metabolically active compounds. It is a structural part of the cell membrane (phospholipids), chloroplasts and mitochondria, and is involved in photosynthesis, glycolysis and respiration. It is a part of sugar phosphates (ADP and ATP), phospholipids (lecithin and choline), phosphoproteins, nucleic acids, nucleoproteins, purine, pyrimidine nucleotides, flavin nucleotides and many co-enzymes viz. NADP, pyridoxyl phosphate and thiamine phosphate. Such important plant processes as photosynthesis, glycolysis, respiration, and fatty acid synthesis are dependent upon the action of the coenzymes -NAD and NADP.
ii. The most essential constituents of plant cells like esters, phosphatides and phospholipids are synthesized by phosphorus when it combines with different organic acids. It also plays an important role in energy transformations and various metabolic activities of plants.
iii. Being a constituent of adenosine phosphate, phospho glyceraldehyde and ribulose phosphate, it helps in basic reactions of photosynthesis and activates several enzymes participating in dark reactions in photosynthesis.
iv. Heavy concentrations of phosphorus are found in the meristematic regions of actively growing plants, where it is involved in the synthesis of nucleoproteins.
v. It is an essential component of deoxyribonucleic acid (DNA), the seat of genetic inheritance in plants and of the various forms of ribonucleic acid (RNA) needed for protein synthesis.
vi. It imparts in early root development, particularly of the lateral and fibrous rootlets. Thus helps in early plant establishment.
vii. It hastens crop maturation including flowering, fruiting and seed formation.
viii. Strength of straw in cereal crops is induced by phosphorus, thus helping to prevent lodging.
ix. It improves crop quality, especially of forages and of vegetables.
x. In legumes, it induces rhizobial activity, nodule formation and thus N fixation.
Deficiency symptoms of phosphorus
i. Phosphorus is mobile and is redistributed from old to young tissues. Young leaves or developing fruits can be nourished from the labile P of older plant tissues even though the soil source is interrupted. Therefore, the older leaves first show deficiency symptoms.
ii. The foliage turns bluish-green. If deficiency continues for longer period then the older leaves become bronzed or develop reddish – brown or purple tints. These symptoms become more prominent during cold then margins may role.
iii. The growth of root and shoot is restricted. Phosphorus deficient plants are thin and spindly. Premature shedding of leaves and flowering occur, and fruiting is also delayed considerably. Plants lacking phosphorus may develop dead necrotic areas on the leaves, petioles or fruits.
iv. In cereals, the foliage turns bluish-green and then strong reddish-purple (due to red anthocyanin pigmentation). Tints develop on the nodes, internodes, leaves and even on heads.
v. Potato tubers grown in phosphorus deficient soils develop rusty lessions in the flesh.
Abundant supply/over dose/toxicity of phosphorus
i. Profuse root growth, particularly of the lateral and fibrous rootlets.
ii. Hastens early crop maturity.
iii. Impairs the uptake of iron and zinc.
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