Function and Deficiency symptoms of Potassium and Toxicity
Functions of Potassium in plants
It is known as the luxuriant nutrient as plants uptake it in huge quantity.
i. Potassium helps in the formation of mechanical tissues in cereals, encourage strong stem and root system resulting into resistance to lodging.
ii. It is essential for converting carbon dioxide and hydrogen into sugars and for translocation of sugars and also for starch formation. Therefore, the element is absolutely necessary for tuber development in tuber crops and is important for grain formation in cereals, and sugar accumulation and translocation in sugarcane.
iii. It helps in the maintenance of cellular organization by regulating the permeability of cellular membranes and keeping the protoplasm in a proper degree of hydration by stabilizing the emulsions of colloidal particles. Thus helps in the maintenance of osmotic potential and water uptake.
iv. It serves as an enzyme activator or cofactor for some 46 enzymes. Its salts stabilize various enzyme systems. It plays a catalytic role in activating several enzymes as incorporation of amino-acids in proteins, synthesis of peptide bonds etc. Presence of potassium is essential for optimal activation of aldehyde dehydrogenase, phosphate acetyle transferase etc.
v. The element is essential for protein synthesis. It plays a vital role in photosynthesis by directly increasing growth and leaf area index and stomatal opening.
vi. It increases resistance in plants against drought, heat frost and various diseases caused by fungi nematodes and other micro-organisms.
vii. In fruit crops, it improves colour, flavour and increases the size and weight of the fruits. It improves the quality of crops like tobacco.
viii. It counteracts the damaging effects of excess nitrogen.
ix. It increases the crop resistance to certain diseases.
Deficiency symptom of potassium in plants
i. Generally, a plant deficient in potassium is stunted in growth with a pronounced shortening of the internodes and have a busy appearance.
ii. The external symptoms of potassium deficiency are easily recognized on the leaves of the plant. A -mottled chlorosis first occurs, followed by the development of necrotic areas at the tip and margin of the leaf. The continued deficiency develops chlorosis between the veins and colouration along the leaf-tips and the margins. The colouration may vary from light grey to bronze, reddish brown or dark brown depending upon the species of the affected plants. The potato and certain Brassica spp. bear crumpled and raised lamina. Acute deficiency results into pale and chlorotic interveinal spaces, whereas leaf tips and margins are found to be scorched and necrotic. Because of the mobility of potassium, these symptoms generally appear first on the more mature leaves. Also, in many cases, there is a tendency for the leaf tip to curve downward and, as in the case of the French bean and potato, marginal regions may roll inward toward the upper surface.
iii. 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.
iv. In root crops like sugar-beet, sweet potato, the roots become slender and they are poorly developed.
v. The deficiency is aggravated more under cold and wet weather. The deficiency reduces resistance of plants against bacterial and fungal infections. The drought and frost tolerance of plant is also found to be reduced.
vi. Translocation of photosynthates and nutrient uptake is adversely affected.
Toxicity of over supply of potassium in plants
Crops/plants maturity is delayed.