**2.3 Photosynthesis**

Phosphorus directly or indirectly regulates the photosynthesis process as a primary substrate, utilizing light energy to form sugars and a three-phosphatecontaining molecule ATP in the presence of chlorophyll, CO2, and water. It should be noted that ATP is the key driver of different metabolic reactions in plant cells that is required for the development of structural and storage components. P is a prime element of the thylakoid membrane and is crucial for the regulation of photosynthetic machinery, viz. PSI, PSII, LHCP, cyt-f, cyt-b, and antenna mobility, as reported by Rychter and Rao [26]. In fact, apoprotein phosphorylation of antenna is a vital step in photosynthesis. Various processes involved in photosynthesis depend largely on the availability of Pi, which is controlled by an increase in photorespiration. Alterations in Pi availability in cytoplasm modulate the activation of multiple enzymes (such as RuBisCO, sedoheptulose-1,7-bisphosphatase, and fructose-1,6-bisphosphatase) and amounts of intermediates of the photosynthetic carbon reduction cycle. Besides, Pi possesses a great role in the partitioning of the photosynthates in various plant tissues and the distribution of newly fixed C between chloroplasts and cytoplasm during starch and sucrose synthesis, respectively.
