1 / 16

Plant Biology Fall 2006

BISC 367 - Plant Physiology Lab Spring 2009. Plant Biology Fall 2006. Notices: General reading Taiz and Zeiger: Chapter 7, Photosynthesis: the Light Reactions. Photosynthesis - light. Photosynthesis (P/S) uses light energy to build carbon compounds

aysel
Download Presentation

Plant Biology Fall 2006

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. BISC 367 - Plant Physiology Lab Spring 2009 Plant Biology Fall 2006 • Notices: • General reading • Taiz and Zeiger: Chapter 7, Photosynthesis: the Light Reactions

  2. Photosynthesis - light • Photosynthesis (P/S) uses light energy to build carbon compounds • CO2 + H2O (CH2O)n + O2 • Inputs: CO2 • H2O • Light • Outputs: Carbohydrate (CHO) • O2 Light energy

  3. Photosynthesis - light • P/S is divided into 2 stages Reductant & NRG are used to reduce CO2 Light NRG oxidizes H2O

  4. Photosynthesis - light P/S takes place in chloroplasts (cp) Stroma lamellae Unstacked membrane Thylakoid Grana lamellae Stacked membranes Light rxns occur here Carbon reduction rxns occur here Stroma

  5. Photosynthesis - light • Pigments (chlorophylls and carotenoids) exist in antenna complexes • Harvest and transfer light NRG to chlorophylls at the reaction centre • NRG is transferred from pigment to pigment by resonance transfer • At the reaction centre NRG is converted to chemical (redox) NRG • Antennal pigment/ reaction centre complexes are also referred to as photosystems • There are 2 photosystems • PSI • PSII

  6. Photosynthesis - light • Light NRG moves down an energy gradient towards the reaction centre

  7. Photosynthesis - light • PSI and PSII operate in series • PSI absorbs far-red light (>680 nm) = P700 • Produces a very strong reductant • PSII absorbs red light (680 nm) = P680 • Produces a strong very strong oxidant • Can oxidize water Ultimate source of e- Z scheme of Photosynthesis

  8. Photosynthesis - light • 4 protein complexes embedded in the thylakoid membrane are involved in the light reactions • PSII • Cytochrome b6f complex • PSI • ATP synthase

  9. Photosynthesis - light • Oxidation of water: • Performed by the oxygen evolving centre (OEC) of PSII • 2H2O O2 + 4e- + 4H+ • Water is extremely stable - oxidation is not easy! • 4H+ are released into thylakoid lumen • OEC is located on lumenal side of membrane

  10. Photosynthesis in an intact plant

  11. Photosynthesis in isolated cps [Fe(CN)6]3- [Fe(CN)6]4- O2 is evolved as e- are passed to Ferricyanide

  12. Some herbicides block e- flow

  13. Photosynthesis – blocking e- transport + + + + + + DCMU - - + + [Fe(CN)6]3- + + + + Oxidized - - Reduced Electron flow is blocked, O2 evolution is inhibited

  14. Photosynthesis – flavin mononucleotide (FMN) DCMU 2 FMN + 2 H2O 2 FMNH2 + O2 2 FMNH2 + 2 O2 2 FMN + 2 H2O2 - O2 is consumed as FMN passes e- to O2 to generated H2O2

  15. O2 can accept e- from PSI • Mehler reaction (light dependent consumption of O2): • O2 + Fdred O2- + Fdox • 5 - 10% of e- generated by PSI react with O2 • Plants have built in systems to “scavange” ROS • SOD (superoxide dismutase): • O2- + O2- + 2H+ H2O2 + O2 • H2O2 must be reduced to prevent reaction with O2- to form the highly toxic hydroxyl radical (OH.)

  16. O2 can accept e- from PSI • Asada-Halliwell pathway reduces H2O2: GSSH GSH NADPH NADP+ Ascorbate Monodehydro- ascorbate PSI H2O2 H2O

More Related