*2.1.3 Nucleic acids*

As a major component of nucleic acids, P is involved in the transfer of genetic materials needed for growth and development from one generation to the succeeding generation. Nucleic acids are polynucleotides that consist of nitrogen-containing aromatic bases attached to a pentose sugar, connected with a phosphate group. DNA and RNA are the two principal classes of nucleic acids that form the largest organic P pool in plants, ranging from 0.3 to 2.0 mg P g−1 dry weight in various crops [25]. Both nucleic acids direct the process of new protein synthesis such as enzymes and determine the inherited traits in living organisms including plants.

#### **2.2 Energy and electron transport**

The role of P in cellular metabolism, mainly energy transport, is of great significance. P is involved in various cellular processes because it is linked with high-energy bonds, and the high-energy P-containing compounds such as phosphoanhydride, acyl phosphate, enol phosphate, etc., transfer energy to acceptor molecules. The phosphates are formed at the sites of energy production and are donated to other molecules at sites of energy consumption. The most common P energy currency is found in ATP, whose hydrolysis releases a great amount of free energy required for multiple cellular processes like macromolecule synthesis, membrane phospholipid formation, nutrient transport, etc. For example, α, β, and γ-phosphate release energy of 13.8, 27.2, and 34.0 kJ mol−1, respectively, after hydrolysis [25]. Similarly, phosphoanhydride bonds are found in di- and triphosphate molecules in guanine, cytosine, uracil, and thymine nucleosides. In gluconeogenesis and saccharide metabolism, guanosine triphosphate (GTP) and uridine triphosphate (UTP) are important electron donors. Phosphorus is an essential part of the structure of triphosphopyridine nucleotide (TPN) that provides a similar transportation function in plants as adenosine

diphosphate (ADP) and adenosine triphosphate (ATP). These nucleotides function as carriers of electrons or hydrogen between sites of oxidation and reduction reactions occurring in photosynthesis and respiration.
