Plant Respiration

• Aerobic Respiration

  • Biological process by which reduced organic compounds are mobilized and subsequently oxidized in a controlled manner
• Primary Role of Respiratory Metabolism

  • Controlled release of free energy, together with its coupling to the synthesis of ATP
• Glycolysis

  • happens in the cytosol
  • Starting material: glucose
  • Products: 2 pyruvate; 4 ATP; 2 NADH
  • Uses: 2 ATP
• TCA Cycle / Krebs Cycle

  • Starting material: Acetyl CoA
  • Products: 1 FADH2; 3 NADH; 1 ATP (GTP) 2 CO2
• Complex I - oxidizes NADH into NAD+
• Complex II - FADH2 is oxidized into FAD+
• Complex IV - pass electron to the final electron acceptor (oxygen) to get water
• Complex V - ATP synthase
• Primary Goal of Cellular Respiration - produce ATP and power other processes
• Why need to go through different processes to produce ATP?

  To oxidize in a controlled manner to control energy
• Another important function of aerobic respiration?


  Provides carbon skeletons for biosynthesis of other molecules
• Difference of Autotrophic and Heterotrophic Respiration

  1. Starting material for plant respiration comes from the products of photosynthesis
  2. High concentration of sugars and O2 in the plant cell environment requires complex regulation of the flow of these compounds
  3. Plant mitochondria do not only function for cellular respiration. It is also important in maintaining redox balance.
• Heterotrophic starting material - Sucrose, starch

  Autotrophic starting material - Sucrose, starch, TP, glucose, DHAP
• Substrate supply can control the rate of transpiration by regulating substrate available for a particular reaction

  • If G-6-P is high, reaction are catalyzed by phosphoglucoisomerase shifts towards the formation of Fru-6-P
• More sucrose needed = Activates Fructose-1,6-bisphosphatase
• If needs glycolysis - activates PP-Fructose-6-phosphate kinase
• Fructose-2,6-bisphosphate activates PP-Fructose-6-phosphate kinase hence promoting glycolysis. On the other hand, it also inhibits Fructose-1,6-bisphosphatase thereby inhibiting sucrose formation
• Fermentation occurs when oxygen is limiting, and NADH and pyruvate accumulates
• Main goal of Fermentation - replenish NADP+ by using NADPH in the process
• If there is no oxygen, what will happen to glycolysis, TCA, and ETC


  Glycolysis will push through however TCA and ETC will not
• When is NAD+ released in Alcoholic Fermentation?


  Upon conversion of acetaldehyde into ethanol
• When is NAD+ released in Lactic Acid Fermentation?


  Upon conversion of pyruvate into lactate
• High Level of ATP, inhibits?

  ETC, Krebs, and Glycolysis
• What activates / promotes ETC?


  High level of ADP
• High light intensity leads to the formation of ROS since there is high concentration of NADPH and low NADP+; hence, the electrons will bind with oxygen
• Pathways plant utilize to prevent formation of ROS

  • Cyclic Electron Flow - electron will be brought back in Cytochrome b6f thus producing more ATP
  • Thermal Dissipation - carotenoids will accept electron since it does not have enough energy to excite oxygen
• Reason why NADPH cannot easily go out of chloroplast?


  NADPH is impermeable in the membrane and does not have transporter
• Malate-Oxaloacetate Shuttle

  • The chloroplast uses NADPH to oxidize Oxaloacetate into Malate
  • Malate will go to the cytosol; then, will be converted into Oxaloacetate and producing NADH in the process
• OMT / DCT

  • Oxoglutarate-malate transporter through nitrogen assimilation
  • Uses NADPH / NADH to remove malate or other compounds from the chloroplast that are capable of releasing NADH in the cytosol
• Triose Phosphate-Phosphate Transporter

  • Increased rate of Calvin Cycle so that more NADPH is used in the chloroplast
  • TPT transports more 3-PGA in the cytosol
  • TP are exported to the cytosol for sucrose synthesis
  • P are imported to the chloroplast for photophosphorylation
• Glycolate / Glycerate Shuttle

  • Photorespiration uses NADPH in the process to relieve excess reductant in the chloroplast
  • RUBP is oxygenated forming glycolate. Glycolate is transported into the peroxisome and will be converted into Glycine.
  • Glycine arrives in the mitochondrion and is converted into serine. In this process, NAD+ is used to produce NADH
• Photorespiration

  • aids in reducing excess reactants
  • has 0 NET NADH
  • NADH from the chloroplast are used in the peroxisome and mitochondrion
• Alternate Electron Pathways in Plants

  1. External NAD(P)H Dehydrogenase
  2. Retonone-Insensitive NADH Dehydrogenase
  3. Cyanide-resistant Respiration
• External NAD(P)H Dehydrogenase

  • Faces the intermembrane space of the mitochondrion
  • Electron enter the main ETC at the ubiquinon level (bypass Complex I)
  • Oxidizes NADH from the cytosol through external dehydrogenases
  • Does not increase proton gradient = no ATP synthesis
• Retonone-Insensitive NADH Dehydrogenase

  • Inner surface of the membrane
  • will only oxidize internal NADH (from TCA or conversion of Glycine to Serine)
  • E- is passed to the ubiquinone = no proton gradient = no atp synthesis
• Cyanide-Resistant Respiration

  • Alternative Respiratory Pathway
  • Involves an oxidase (Alternative Oxidase / AOX) that is insensitive to the inhibition of cyanide, azide, or carbon monoxide
  • AOX works like Complex IV (electrons to oxygen = water)