Sugarcane bioethanol — R&D for Productivity and Sustainability

PHOTOSYNTHESIS IN SUGARCANE AND ITS STRATEGIC IMPORTANCE TO FACE THE GLOBAL CLIMATIC CHANGE

Souza, Amanda Pereira de; Buckeridge, Marcos Silveira;

Resumo:

The photosynthetic process consists of two couple reaction. The first, called photochemical phase, refers to the reactions related to light capture, electron transport and the formation of reducing power (i.e. NADPH and ATP). The second phase is the biochemical, where carbon dioxide (CO2) is captured and transformed into compounds that link carbon atoms together and therefore retain the energy absorbed by the light reaction (BUCKERIDGE et al., 2008). In the photochemical reactions, the light captured by leaves is capable to provoke changes in chlorophyll molecules present in the chloroplasts and these changes start the transportation of electrons through the electron transport chain, formed by highly specialized proteins. At the end of the process one NADPH and one ATP molecule are formed. These compounds carry the energy and are used in the biochemical phase of photosynthesis. During this phase, CO2 enters the mesophyl through the stomata (Figure 1), and it is assimilated by an enzyme called Rubisco (Ribulose-1,5- bisfosphate carboxylase/oxygenase). The process of carbon assimilation starts when the carbon of CO2 is incorporated into a molecule of ribulose- 1,5-bisphosphate (RuBP), what starts the so called Calvin Cycle. This cycle forms compounds with 3 carbon atoms, named 3-phosphoogliceric acid (3-PGA). Every two 3-PGAs formed, one molecule of sugar with six carbons is synthesized. The sugars are then polymerized to starch stored in leaves or transported to the growing organs as sucrose. The plants use this process to perform a type of photosynthesis that is called C3, since the enzyme that captures the CO2 inside the cell forms primarily a compound containing 3 carbon atoms (3-PGA). However, certain plants (e.g. sugarcane, maize and sorghum) have been modified during evolution so that they contain complementary metabolic pathway where, instead of incorporating carbon from CO2 in a 3-carbon acid, they incorporate into a 4-carbon acid and because of that this type of photosynthesis is called C4. We even refer to a given plant species as a C4 or C3 species depending on its metabolism.

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DOI: 10.5151/BlucherOA-Sugarcane-SUGARCANEBIOETHANOL_36

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Como citar:

SOUZA, Amanda Pereira de; BUCKERIDGE, Marcos Silveira; "PHOTOSYNTHESIS IN SUGARCANE AND ITS STRATEGIC IMPORTANCE TO FACE THE GLOBAL CLIMATIC CHANGE", p. 359 -364. In: Sugarcane bioethanol — R&D for Productivity and Sustainability. São Paulo: Blucher, .
ISBN: 978-85-212-0822-8, DOI 10.5151/BlucherOA-Sugarcane-SUGARCANEBIOETHANOL_36