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Nitrogen (N) is an important macronutrient needed by plants for their growth. Nitrogen exists in two forms: organic and inorganic. Nitrogen cycles in nature in these two forms. Nitrate and ammonium, inorganic forms of N, are the most common N source for plants, whereas amino acids and urea are the organic sources of N. The expression of genes for growth and development, including physiological and metabolic processes of plants can also be controlled by N in the form of nitrates and other forms where it acts as a signal molecule, alongside their role in nutrition. The mechanism of N signaling in the regulation of genetic expression is not fully understood, even though many genes are known to be expressed/repressed during an increase or decrease of N. Nitrogen occurs in organic and inorganic forms, which are also present in amino acids as well as peptides. Nitrogen used by plants is adjusted according to requirement, and thus spatial and temporal activity is well balanced. N uptake is dependent on various factors such as change in environment, temperature, fertilization, soil pH, and precipitation. Most plants fulfill their need for N through the processes of bacterial nitrification and fertilization. Uptake, assimilation, translocation, aging, recycling, and remobilization are the levels through which plants use nitrogen. Pathogen invasion or heavy metals are some environmental aspects that spontaneously actuate senescence and remobilization of nitrogen. GLN1, GDH, and ASN are the genes expressed during biotic stresses. They enhance the process of N remobilization as reported by various studies. Abiotic stresses affect the uptake and absorption of N by plants, which includes salt stress, drought stress, and intense temperature stress. Abiotic stresses such as drought, aluminum toxicity, and nutrient insufficiency (particularly P and N) are the major elements responsible for extensive crop losses, up to 50% worldwide. Abiotic stresses such as salinity, intense temperature, aluminum poisoning, drought, and flooding also influence nitrogen fixation by legume. Drought stress extremely affects nitrogen fixation, which is highly susceptible to it, and declines even before the decrease in leaf photosynthesis. |
