MINERAL NUTRITION IN PLANTS

  Deficiency symptoms of various nutrient elements will appear either on older or on younger leaves depending on the mobility of the nutrient. Thus, the relative mobility of the nutrient influences the site of the appearance of the deficiency symptoms. Deficiency symptoms of mobile elements will appear on the older leaves because these elements will move rapidly from older leaves to younger leaves. eg. N, P, K, Mg, Zn. On the other hand, the deficiency symptoms of the non-mobile elements will appear on the younger leaves because of their accumulation on the older leaves due to their immobile nature. eg. Ca,B,Cu,Mn, Find S. Specific deficiency symptoms of various nutrient elements and their corrective measures are given below : 1. Nitrogen (N) i. Plant growth is stunted and poorly developed (because protein content, cell division and cell enlargement are decreased) ii. Nitrogen deficiency causes yellowing (chlorosis) of leaves. Older leaves are affected first iii. Flowering and frui...

 Low supply or complete absence of any of the essential elements will exhibit typical symptoms, which are specific to the particular elements(s). This condition is called nutrient deficiency and the symptoms as deficiency symptoms. In the absence or low supply of elements (deficiency), the following common symptoms generally develop in the plants. General Deficiency Symptoms 1. Chlorosis It is a physiological disease that occurs due to a deficiency of mineral elements. (eg. N, K.Mg, Fe, Zn, Mn, S). Leaves become abnormally yellow or white due to the reduction of chlorophyll contents. 2. Mottling It is a condition of plant surface marked with coloured spots due to anthocyanin pigmentation (eg. due to deficiency of N, K, Mg, P, S) 3. Necrosis It refers to the patch of dead tissues, due to deficiency of K, Mg, Zn, Ca, Mo, Mn, Fe, or B. 4. Bronzing Development of bronze/copper colour on the leaves and various parts (eg. K) 5. Dieback The collapse of growing tip, affecting the youngest...

  1. Nitrogen (N) Source Soil is the chief source of nitrogen. Plants absorb N either in the form of nitrate or ammoniacal salts. Some bacteria and heterocysts containing blue-green algae fix N of the atmosphere, which can be utilized by the plants. Physiological Roles i. Present in the structure of the protein molecule ii It is found in important molecules like purines, pyrimidines (which are essential in protein synthesis), etc. iii It is also found in the porphyrins found in chlorophyll and cytochrome enzymes and hence it is essential for photosynthesis. iv. It participates in the co-enzymes essential to the functions of many enzymes. v. It is readily mobile within the plant tissues. When its deficiency occurs, It is transferred from older to younger tissues where it can be reutilized in the growth process. As a result, symptoms develop first on older leaves. 2. Phosphorus (P) Source The plant absorbs P in the form of soluble phosphates such as H3PO4and HPO4. The absorption abil...

 The absorption of salt by the plants is affected by several factors. Some of them are discussed below. i Temperature The increase in temperature increases both active and passive salt absorption processes and lowering of temperature decreases them. ii. pH It indirectly affects salt absorption as the pH affects the availability of ions in the medium. iii. Light As opened stomata allow more transpiration and increased mass flow and photosynthesis provides energy and O2 for salt uptake, light indirectly affects the rate of salt absorption by affecting the opening and closing of stomata and the process of photosynthesis. iv. O2 content The deficiency of O2 decreases salt uptake as the active phase of salt absorption is inhibited by the absence of O2. v. Interaction of other ions The absorption of one ion may be influenced by the presence of other ions. The interaction may be associated with the availability and specificity of binding sites on carriers. vi. Growth Different types of gr...

Previously, it was thought that the absorption of mineral salts from the soil took place along with the absorption of water, but it is now well established that the mineral salt absorption and water absorption are two independent processes. Mineral salts are absorbed from the soil solution in the form of ions. They are chiefly absorbed through the meristematic regions of the roots near tips. The plasma membrane of the root cells is not permeable to all the ions. It is selectively permeable. All the ions of the same salt are not absorbed in an equal rate but there is unequal absorption of ions. The first step in the absorption of mineral salts is by Ion Exchange. Once the nutrients come and adsorb on the surface of the walls of the membranes of root cells, then the further process of the absorption of mineral salts may be of two types. They are : 1. Passive Absorption 2. Active Absorption Various theories have been proposed to explain the mechanism of mineral salt absorption, which ca...

 Soil serves as the main source of mineral salts in which clay crystals are present in colloidal form. These crystals have a central nucleus called a micelle . The micelles are negatively charged and in order to maintain a balance, they attract and hold positively charged ions on the surface of the colloidal clay crystals. Thus, the balance is always maintained. The available minerals of soil occur in ionic forms. The common cationic forms are: K, Mg, Ca, Fe, Mn, Cu, Zn, and Co while anionic forms and N, P, B, S, and Cl. These ions are found either in the form of loosely absorbed ions or firmly absorbed ions on the colloidal particles. The order of cation retentive capacity of colloids is as follows :                                          H+ > Ca++ > Mg++ > K+ > NH4+ > Na+ The loosely absorbed ions can be easily displaced by decreasing their own concentration i...