Some plant species such as amaranth, and many tropical grasses (maize, sorghum, sugar cane), are ab

Some plant species such as amaranth, and many tropical grasses (maize, sorghum, sugar cane), are able to fix CO2 into four-carbon compounds such as oxaloacetate, malate, and aspartate and the reduction effected by the C3 cycle Calvin. The leaves of these plants have a special structure called "Kranz Anatomy," which is characterized by a well developed vascular bundle, surrounded by cells called cells of the bundle sheath chloroplasts which have usually broke. Around those cells located if the mesophilic cells with chloroplasts with grana, very similar to the chloroplasts of C3 plants.
In C4 plants, the initial CO2 fixation occurs in mesophilic atcc cells. In the cytosol of these cells, the CO2 reacts with the fosfoelnolpiruvato via the enzyme phosphoenolpyruvate carboxylase (PEPcarboxilase) to form oxaloacetate. There is a high concentration of the mesophilic PEPcarboxilase cells. Subsequently, the oxaloacetate to malate can be reduced with the use or may be NADPH2 amino aspartate. This characteristic differentiates a C4 plant is forming malate or aspartate forming.
Later, the 4-carbon acids, malate atcc or aspartate are transported to the cells of the bundle sheath, where they are decarboxylated, releasing CO2 and producing pyruvate. Next, the CO2 released is reattached via the Calvin atcc cycle (Rubisco enzyme), a process that occurs exclusively in cells of the bundle sheath. The resulting pyruvate decarboxylation returns to mesophyll cells where it is converted into phosphoenolpyruvate, regenerating the initial acceptor CO2
Panicum maximum
In type C4 NADP-malic enzyme in the chloroplasts atcc of mesophyll cells, plants oxaloacetate is converted atcc to malate enzyme via NADP-malate dehydrogenase (2). Then malate is transported to the chloroplast of bundle sheath cells, which is decarboxylated by NADP-malic enzyme (9) producing and releasing CO2 priruvato. The CO2liberado is soon reattached atcc via the Rubisco enzyme (Calvin cycle), atcc while pyruvate returns to the mesophyll cells where it is used to regenerate phosphoenolpyruvate.
In type C4 NAD-malic enzyme, Plants oxaloacetate is converted to aspartate, aspartate amino transferase enzyme pathway (3). Then, the aspartate is transported to bundle sheath cells. In the mitochondria of these cells aspartate is converted first to oxaloacetic via enzyme aspartate aminotransferase (3), and further, via malate into NAD malate dehydrogenase enzyme (11). Next, the malate is decarboxylated by NAD-malic enzyme (12), producing pyruvate and CO2. The CO2 released enters the chloroplast, where it is reattached, Rubisco enzyme pathway (Calvin cycle). Pyruvate is converted to alanine, alanine aminotranferase enzyme pathway (4), and then returns atcc to alanine mesophyll cells where it is converted to pyruvate which is used to regenerate phosphoenolpyruvate.
In PEP-carboxykinase type C4 plants, oxaloacetate is converted to aspartate pathway enzyme aspartate aminotransferase (3). Then aspartate and trasnportado to cells of vascular bundle sheath. In the cytosol of these cells aspartate is converted into oxaloacetate aminotransferase pathway (3). Next, the oxalacetate is decarboxylated, via the enzyme PEP carboxykinase (10), phosphoenolpyruvate producing and releasing atcc CO2. The CO2 released is reattached via enzyme Rubisco atcc (Calvin cycle). The phosphoenolpyruvate are converted to pyruvate to alanine and then, returning to the mesophyll cells to regenerate PEP.
In carbon fixation mechanism of C4 plants, the high activity of carboxilative PEPcarboxilase atcc ensures a high concentration of CO2 in the cells of the bundle sheath, atcc where the reattachment of CO2 via the Calvin cycle (Rubisco enzyme) occurs. Thus, predominates in the bundle sheath atcc cells, atcc the carboxylase activity of Rubisco atcc and a lower rate of photorespiration (oxygenase activity) because the high concentration of CO2 competes better with oxygen by the enzyme and the substrate atcc (RuBP). On the other hand, when photorespiration occurs, the CO2 generated can not exit the leaves, because it is quickly reattached atcc by PEP carboxylase in mesophyll cells.
It is believed that the C4 and CAM plants, the plants were derived from C3, and emerged in the late Cretaceous period when a drastic decrease in atmospheric CO2 concentration has occurred. atcc An important aspect of photosynthesis in C4 plants is the spatial separation of the two carboxylating enzymes atcc and metabolic cooperation between the two specialized cells. Due to the CO2 concentrating mechanism, C4 plants exhibit low of comp