In C4 photosynthesis, malate is produced in mesophyll cells and is shuttled to the bundle sheath cells.
In C4 photosynthesis, malate serves as an important intermediate molecule that aids in the efficient capture and concentration of carbon dioxide (CO2) in plants
In C4 photosynthesis, malate serves as an important intermediate molecule that aids in the efficient capture and concentration of carbon dioxide (CO2) in plants. This process allows plants to minimize wasteful photorespiration and enhance their ability to thrive in hot and arid environments.
C4 plants have specialized anatomical and biochemical adaptations that enable them to separate the initial CO2 fixation from the Calvin cycle, which ultimately produces sugars. This separation occurs in two distinct types of cells: the mesophyll cells and the bundle sheath cells.
In C4 plants, malate is produced in the mesophyll cells, which are present in the interior layers of the leaf. These cells contain high amounts of phosphoenolpyruvate carboxylase (PEP carboxylase), an enzyme that catalyzes the fixation of CO2 into oxaloacetate. Oxaloacetate is then immediately converted to malate through a series of enzymatic reactions.
The malate produced in the mesophyll cells is then actively transported across the cell membrane and into the bundle sheath cells. This transport occurs via specialized membrane transport proteins that facilitate the movement of malate molecules between cells.
Upon entering the bundle sheath cells, malate is decarboxylated to release CO2, which then enters the Calvin cycle for further sugar synthesis. The released CO2 is then refixed into organic molecules using the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco).
The diffusion of CO2 from the mesophyll cells to the bundle sheath cells is unidirectional, meaning that CO2 cannot move back from the bundle sheath cells to the mesophyll cells. This prevents the loss of CO2 through photorespiration and contributes to the increased efficiency of C4 photosynthesis.
Overall, the production and shuttling of malate in C4 plants is a crucial mechanism for concentrating CO2 near the site of Rubisco activity in the bundle sheath cells. This enables C4 plants to overcome the limitations imposed by hotter and drier climates, enhancing their photosynthetic efficiency and promoting their survival in such environments.
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