Physiological Mechanisms of Nitrogen Absorption and Assimilation in Plants under Stressful Conditions

Nitrogen is the most important element for plant growth and development. In the cell, it is present as constituent of proteins, amino acids, nucleic acids, coenzymes, vitamins, chlorophylls, hormones, and functional groups of enzymes. It is a major part of chlorophyll and the green color of plants. It is a key constituent of nucleic acids that serve as genetic material and regulate vital processes like growth, reproduction, and heredity. Being a principal macronutrient, N has a special place in plant nutrition, and plants require it in large amounts. Though N is the most abundant element in our atmosphere, majority of the plants cannot utilize it directly in the elemental form. An adequate supply of N in the soil is essential to maintain proper growth and yield of crops. The availability of N in the soil is due to N2 fixation by symbiotic and nonsymbiotic bacteria; mineralization of organic matter, manure, and animal waste products; or application of inorganic N fertilizers. Though the natural sources can make significant contributions to soil N levels, with the advent of modern agricultural practices, to CONTENTS