Photosynthesis, Respiration

Photosynthesis, Respiration and Assimilation

Photosynthesis Definition: - a process in which solar energy is converted into chemical energy 6CO 2 + 12H 2 O --> C 6 H 12 O 6 + 6O 2 + 6H 2 O Location: chloroplasts Two parts: 1. Light dependent reaction :- to generate NADPH and ATP required for subsequent carbon reduction - Phototsystem I LHC I, P700 (reaction centre chlorophyll a, A max 700 nm) - Photosystem II LHC II, P680 (reaction centre chlorophyll a, A max 680 nm) - cytochrome b 6 f complex - ATPase 2. Light independent reaction - Calvin cycle (photosynthetic carbon reduction cycle) i. carboxylation: fix CO 2 ii. reduction: 3-carbon acids triose phosphate (G3P); consume ATP and NADPH iii. regeneration: triose phosphate (G3P) RuBP; consume ATP

Types of Plastids Proplastid fruit petals roots Chromoplast leaves stems non-photosynthetic storage tissues Amyloplast senescing leaves and stems Chloroplast leaves and stems Adapted from: Hopkins and Huner (2004) Introduction to Plant Physiology. 3 rd ed.

Photosynthesis: Light Dependent and Light Independent Reactions H 2 O CO 2 Light Chloroplast NADP + Light Reactions ADP ATP NADPH Calvin cycle Cytoplasm O 2 [CH 2 O] n (sugars) Adapted from: Campbell, Reece & Meyers. 2005. Biology 7 th ed.

Photosynthesis Definition: - a process in which solar energy is converted into chemical energy 6CO 2 + 12H 2 O --> C 6 H 12 O 6 + 6O 2 + 6H 2 O Location: chloroplasts Two parts: 1. Light dependent reaction :- to generate NADPH and ATP required for subsequent carbon reduction - Phototsystem I LHC I, P700 (reaction centre chlorophyll a, A max 700 nm) - Photosystem II LHC II, P680 (reaction centre chlorophyll a, A max 680 nm) - cytochrome b 6 f complex - ATPase 2. Light independent reaction - Calvin cycle (photosynthetic carbon reduction cycle) i. carboxylation: fix CO 2 ii. reduction: 3-carbon acids triose phosphate (G3P); consume ATP and NADPH iii. regeneration: triose phosphate (G3P) RuBP; consume ATP

Electron Transport System in the Thylakoid Membrane stroma thylakoid Chloroplast outer envelope inner envelope granum (a stack of thylakoids) ADP+P i H + ATP lumen stroma NADP + NADPH Cytochrome b 6 f FD 2H + complex ATP synthase thylakoid membrane lumen PS II PQ PQH 2 2H + Fe-S PC PC PS I 2H 2 O O 2 + 4H + Adapted from: Hopkins and Huner (2004) Introduction to Plant Physiology. 3 rd ed.

Photosynthesis Definition: - a process in which solar energy is converted into chemical energy 6CO 2 + 12H 2 O --> C 6 H 12 O 6 + 6O 2 + 6H 2 O Location: chloroplasts Two parts: 1. Light dependent reaction :- to generate NADPH and ATP required for subsequent carbon reduction - Phototsystem I LHC I, P700 (reaction centre chlorophyll a, A max 700 nm) - Photosystem II LHC II, P680 (reaction centre chlorophyll a, A max 680 nm) - cytochrome b 6 f complex - ATPase 2. Light independent reaction - Calvin cycle (photosynthetic carbon reduction cycle) i. carboxylation: fix CO 2 ii. reduction: 3-carbon acids triose phosphate (G3P); consume ATP and NADPH iii. regeneration: triose phosphate (G3P) RuBP; consume ATP

C 3 Photosynthesis Chloroplast CO 2 3-phosphoglycerate (3C) ATP ADP Ribulose-1,5-bisphosphate Calvin cycle (RuBP; 5C) ADP ATP 1, 3-bisphosphoglycerate NADPH NADP + Cytoplasm Glyceraldehyde-3-phosphate (G3P) Sugars Examples of C 3 plants: rice, wheat, soybean, and potato carboxylation reduction regeneration

C 4 Photosynthesis Spatial separation MC BSC Mesophyll cell CO 2 Phosphoenolpyruvate Oxaloacetate (3C) PEP carboxylase (4C) MC Malate / aspartate (4C) Cytoplasm Edwards et al. 2001. Plant Physiol. 125:46-49 Mesophyll cells (MC) -chloroplasts: stroma devoid of Rubisco thylakoids PS I and PS II highly active Bundle sheath cells (BSC) -chloroplasts: stroma replete with Rubisco thylakoids lacking PS II Examples of C 4 plants: maize, sorghum and sugarcane Malate / aspartate (4C) Pyruvate CO 2 Bundle sheath cell Chloroplast Calvin cycle sugars Cytoplasm

Anatomy of C 3 and C 4 Leaves (Plant Physiology Online; http://3e.plantphys.net/article.php?ch=e&id=290)

Crassulacean Acid Metabolism (CAM) Temporal separation CO 2 is taken up during the night The prefixed CO 2 is stored in the vacuoles as malate Malate is transported out of the vacuole during the day for incorporation into carbohydrates via the Calvin cycle Examples of CAM plants: pineapple, cacti, agave and orchids [Dodd et al. 2002. Journal of Experimental Botany 53(369): 569-580]

Respiration Respiration is a cellular process in which hexose is oxidised to CO 2 and water, accompanied by the release of energy Stages: 1. Breakdown of starch and sucrose 2. Conversion of hexose sugars to pyruvate glycolysis 3. Oxidation of pyruvate by the TCA (tricarboxylic acid) cycle or Krebs cycle 4. Transfer of electrons from NADH and FADH 2 to O 2 and the accompanying conversion of redox energy to ATP mitochondria electron transport chain Respiration provides carbon skeletons for the biosynthesis of other molecules

Role of Respiration in the Biosynthesis of Cellular Molecules Nucleic acids ATP NAD Cytokinins Pentose-P Starch Glucose-6-P Triose-P Cellulose Glycerol Triglycerides Phospholipids Shikimic acid Phosphoenolpyruvate Auxin Amino acids Other amino acids Protein Aspartate Other amino acids Alkaloids Protein Oxaloacetate Citrate TCA cycle α-ketoglutarate Other amino acids Protein Pyruvate AcetylCoA Glutarate Alanine Fatty acids Isoprenoids Protein Porphyrins Carotenoids Gibberellins Terpenes Chlorophyll Cytochrome Phytochrome Adapted from: Hopkins and Huner (2004) Introduction to Plant Physiology. 3 rd ed.

Interaction among Chloroplast, Cytoplasm and Mitochondrion Light CO 2 O2 Mitochondrion Chloroplast Calvin cycle Triose-P Starch Ethanol CO 2 anaerobic aerobic Triose-P Pyruvate Sucrose Pyruvate FADH 2 TCA cycle ATP NADH Cytoplasm Adapted from: Hopkins and Huner (2004) Introduction to Plant Physiology. 3 rd ed.

Photorespiration * Photorespiration = photosynthetic carbon oxidation cycle = C 2 glycolate cycle It involves three cellular compartments: - chloroplast - peroxisome - mitochondrion Light dependent process O 2 is taken up (oxygenase activity of Rubisco) and CO 2 is released It is counterproductive to photosynthetic CO 2 fixation But it protects the plants against abiotic stress caused by light, drought and salinity Reumanna and Weber (2006) Biochimica et Biophysica Acta-Molecular Cell Research 1763 (12): 1496-1510

Respiration, Photorespiration and Photosynthesis Dark Light Respiration Respiration Photosynthesis O 2 CO O CO 2 O 2 2 CO 2 2 O 2 CO 2 Photorespiration Adapted from: Hopkins and Huner (2004) Introduction to Plant Physiology. 3 rd ed.

Photosynthesis, Respiration and Photorespiration in Higher Plants Kruse et al. (2005) Photochem. Photobiol. Sci. 4: 957-970

Plant Nutrients Element Available Form Concentration in dry matter (mmol/kg) Macronutrients Hydrogen Carbon Oxygen Nitrogen Potassium Calcium Magnesium Phosphorus Sulfur H 2 O CO 2 O 2, CO 2 NO 3, NH 4 K + Ca 2+ Mg 2+ 2 - H 2 PO 4, HPO 4 2 - SO 4 60,000 40,000 30,000 1,000 250 125 80 60 30 Micronutrients Chlorine Boron Iron Manganese Zinc Copper Nickel Molybdenum Cl _ 3 - BO 3 Fe 2+ Mn 2+ Zn 2+ Cu 2+ Ni 2+ MoO 4 2-3.0 2.0 2.0 1.0 0.3 0.1 0.05 0.001 Adapted from: Hopkins and Huner (2004) Introduction to Plant Physiology. 3 rd ed.

Modes of Solute Transport across Membranes Ca 2+ - - 2-, NO 3, H 2 PO 4, SO 4 O 2, CO 2, NH 3 K + Channel protein Carrier proteins (transporters) Membrane Confo ormational change Confo ormational change ATP ADP + Pi Simple diffusion Facilitated diffusion Active transport Passive transport Adapted from: Hopkins and Huner (2004) Introduction to Plant Physiology. 3 rd ed.

Nitrogen Assimilation Nitrogen N 2 constitutes 78% by volume of the atmosphere The 4th most abundant nutrient element in plants Essential constituent of proteins, nucleic acids, hormones, chlorophyll etc. Higher plants are not able to convert N 2 into a biologically useful form Depend on free-living prokaryotes or nitrogen-fixing symbionts Nitrogen in the form of NO 3 or NH 4 is absorbed by the roots

Nitrogen Cycle Atmospheric N 2 Biological N 2 fixation Bacteria Cyanobacteria (60%) Industrial N 2 fixation (30%) Electrical N 2 fixation (10%) Denitrification Thiobacillus denitrificans NH 3 NO 2 NO 3 Nitrosomonas, Nitrococcus Soil Nitrogen Pool Nitrobacter Ammonification Uptake Decaying biomass Animal biomass Plant biomass Adapted from: Hopkins and Huner (2004) Introduction to Plant Physiology. 3 rd ed.

Symbiotic Nitrogen Fixation Host Nodule-forming Leguminous species Sesbania Glycine max (Soybean) Lens (Lentil) Pisum (Garden pea) Non-leguminous species Parasponia Alnus (alder) Myrica (bayberry) Casuarina (pine) Non-nodule-forming Azolla (aquatic fern) Microsymbiont Azorhizobium Bradyrhizobium japonicum Rhizobium leguminosarum Rhizobium leguminosarum Rhizobia Frankia Frankia Frankia Anabaena Hopkins and Huner (2004) Introduction to Plant Physiology. 3 rd ed.

End of lecture