In which cell type initial carboxylation reaction occurs in $ {C_3} $ and $ {C_4} $ plants?

Hint : $ {C_4} $ and $ {C_3} $ plants are plants having different ways of fixing carbon. In the C3 plants, the first compound form is of 3 carbon ( Phosphoglyceric acid ) while in C4 plants the first compound is of 4 carbon ( Oxaloacetic acid ) . $ {C_3} $ and $ {C_4} $ carbon fixation or the Hatch–Slack pathway is one of the three known photosynthetic processes of carbon fixation in plants .

Complete Step By Step Answer:
Plants : The Calvin cycle takes place in the mesophyll cells. The initial carboxylation reaction occurs in the mesophyll cells. A single cell is required for carbon fixation. The primary acceptor of $ C{O_2} $ in $ {C_3} $ plants are Ribulose 1,5-bisphosphate ( RUBP) . RUBP has 5 carbons . The primary $ C{O_2} $ fixation product in the $ {C_3} $ cycle is Phosphoglyceric acid ( PGA) . Which is 3 carbon compounds. $ {C_3} $ carbon fixation is the most common of the three metabolic pathways for carbon fixation in photosynthesis along with $ {C_4} $ and Crassulacean acid metabolism (CAM) . The process converts carbon dioxide and ribose 5 phosphates into two molecules of 3- phosphoglycerate. The reaction occurs in all the plants as the first step of the Calvin cycle.
 $ {C_4} $ plants : The Calvin cycle takes place in the bundle sheath cells. The initial carboxylation reaction occurs in the mesophyll cells. Two cells are required for carbon fixationThe primary acceptor of $ C{O_2} $ in $ {C_3} $ plants are Phosphoenolpyruvate ( PEP) . PEP has 3 carbons . The primary $ C{O_2} $ fixation product in the $ {C_4} $ cycle is Oxaloacetic acid ( OAA ) . Which is four-carbon compounds $ {C_4} $ carbon fixation or the hatch slack pathway is a photosynthetic process in some plants. It is the first step in extracting carbon from carbon dioxide to be able to use it in sugar and other biomolecules. $ {C_4} $ refers to the four-carbon molecule that is the first product of this type of carbon fixation .

Note :
Major difference between $ {C_4} $ and $ {C_3} $ plants is photorespiration. $ {C_3} $ plant undergoes photorespiration also called the $ {C_2} $ cycle while $ {C_4} $ does not due to the presence of Kranz anatomy.The regions where these crops are grown in are often hot and dry, meaning they could benefit from the energy-saving mechanisms of $ {C_4} $ photosynthesis. While $ {C_3} $ photosynthesis has more room for improvement .