Plants synthesize amino acids primarily using simple inorganic nitrogen compounds obtained from the soil. The key soil-based compounds that contribute to amino acid synthesis include:
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Nitrate (NO3-): This is often a primary source of nitrogen for plants. They absorb nitrate from the soil, which is then reduced to ammonium (NH4+) inside the plant.
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Ammonium (NH4+): Plants can take up ammonium directly from the soil. Ammonium is a readily usable form of nitrogen for synthesizing amino acids.
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Urea: Some plants can utilize urea, which is a nitrogen-containing compound that can be broken down into ammonium in the soil, providing a source of nitrogen.
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Nitrogen Gas (N2): In some instances, certain plants, particularly legumes, form symbiotic relationships with nitrogen-fixing bacteria (like Rhizobia) that convert atmospheric nitrogen (N2) into ammonia (NH3) in the root nodules.
Once absorbed, these nitrogen compounds are incorporated into organic molecules through metabolic pathways like the glutamine synthetase-glutamate synthase (GS-GOGAT) cycle and transamination reactions, ultimately leading to the synthesis of various amino acids. Additionally, plants also require carbon sources, which they derive from photosynthesis, to build amino acids.