Bachelor’s Degree Programme (BSCG) – Plant Physiology and Metabolism Assig. Answer | BBYCT–137(Q-2)
2. a) Enumerate the criteria of essentiality of a mineral nutrient.
b) Differentiate between macro and micronutrients. Make a list of trace elements.
c) Describe the structure of mycorrhiza. Comment on the role of mycorrhizal root association in mineral nutrition
a) Essential Elements – An essential element is the one which has a specific structural or physiological role and without which plants cannot complete their life cycle.
Amon and Stout proposed criteria for knowing the essentiality of an element. They are :
(i) It is indispensable for the growth of plant.
(ii) The element is directly involved in the nutrition
of plants. It becomes a component of either a structural or functional molecule. The element may additionally have a corrective effect of mineral balance and other soil conditions.
(iii) A plant is unable to complete its vegetative or reproductive phase in the absence of the element,
(iv) The element cannot be replaced by any other element.
(v) The absence or deficiency of the element produces
disorders that are a direct result of the lack or deficiency of the element.
(vi) The element alone can correct the disorders produced by its absence or deficiency.
-> 16 elements have been found to be essential. They are C, H, O, N, P, K, S, Mg, Ca, Fe, B, Mn, Cu, Zn, Mo, Cl. Nickel has been made the seventeenth essential element
b) Micro-nutrients – i) Required in very minute quantities.
ii) Prevents diseases.
iii) Overconsumption of Vitamins leads to liver and nerve damage.
iv) Available in a minute concentration in the body, less than 1 mg/gm.
Macronutrients – i) Required in larger quantities.
ii) Provides energy.
iii) Overconsumption of macro-nutrients results in cardiovascular diseases, diabetes, obesity, etc.
iv) Available in high concentration in the body, equal to 1 mg or 1000 microgram.
-> Lists of Trace Elements are:
c) The mutually beneficial, symbiotic relationship between fungi and plant roots. Symbiosis begins when fungal spores germinate and emerging threadlike structures, called hyphae, enter the epidermis of plant roots. After colonization of the root, the fungus sends out a vast network of hyphae throughout the soil to form a greatly enhanced absorptive surface area. This results in improved nutrient acquisition and uptake by plant roots, particularly elemental phosphorus (P), zinc (Zn), manganese (Mn) and copper (Cu) and water. In return, the plant provides carbohydrates for the fungi. There are more than 150 species of mycorrhizal fungi found around the world in all types of soils and climates.
The Role of the Mycorrhizal Symbiosis in Nutrient Uptake of Plants and the Regulatory Mechanisms Underlying These Transport Processes. The mycorrhizal fungus provides the host plant with nutrients, such as phosphate and nitrogen, and increases the abiotic (drought, salinity, heavy metals) and biotic (root pathogens) stress resistance of the host. In return for their beneficial effect on nutrient uptake, the host plant transfers between 4 and 20% of its photosynthetically fixed carbon to the mycorrhizal fungus.