Plant Cell, Development & Ultrastructure

Transcription

1 PCDU Lecture Plant Cell, Development & Ultrastructure Plant Cell Biology Labs Download at:

2 Peroxisomes (Microbodies/) Catabolism of Fatty Acids

3 Catabolism of Fatty Acids Glyoxysomes in Fatty Acids Storage Tissues Uricosomen in Stickstoff-speichernden Geweben Katalase Peroxisomes In Leaves Catabolism of Fatty Acids

4 Nitrogen Storage in Uricosomes

5 Histochemical Test for Catalase DAB H 2 O 2 + DAB Diaminobenzidin

6 Import of Peroxisomal Membrane Proteins Pre-Peroxisome Mature Peroxisome Lipid import Peroxisomal membrane proteins (PMPs) enter the ER, are sequestered in specialized regions and bud from the ER to form peroxisomal pre-compartments. These become capable of importing PTS1/PTS2 containing proteins and develop into mature peroxisomes or fuse with existing peroxisomes. Enlarged peroxisomes can divide by fission.

7 Import of Peroxisomal Membrane Proteins Fatty Acid Import by Peroxisomal ABC-Transporters ATP NBF cytoplasm 6 TMDs yeast & mammals plants lumen NBF = Nucleotide binding fold TMD = Transmembrane domain ABC = ATP-binding Cassette dimer fused dimer peroxisomal ABC-transporter CTS = comatose (mutant seeds do not germinate) Dietrich et al There are ca. 130 Genes in the Arabidopsis Genome Coding for ABC-Transporters

8 Import of Metabolites into Peroxisomes Fatty acid import by ABC-transporters Acyl-CoA-handover PXA1/2 Fulda, M. et al. (2004) Plant Cell 16:

9 Import of Peroxisomal Membrane Proteins Lipid import PTS1/PTS2 = Peroxisome-Targeting Signals PTS1: C-terminal tripeptide SKL PTS2: N-terminal R(X 6 )(H/Q)ALF Peroxisomal membrane proteins (PMPs) enter the ER, are sequestered in specialized regions and bud from the ER to form peroxisomal precompartments. These become capable of importing PTS1/PTS2 containing proteins and develop into mature peroxisomes or fuse with existing peroxisomes. Enlarged peroxisomes can divide by fission.

10 Protein Import into Peroxisomes Luminal (Matrix) Proteins: Role of Cytosolic Receptors PEX5/6 and PEX7 PEX7 PTS1: C-Terminal Tripeptide SKL Stanley et al. (2007) FEBS Lett 581: PTS2: N-terminal R(X6)(H/Q)ALF

11 Protein Import into Peroxisomes Luminal (Matrix) Proteins: Role of Cytosolic Receptors PEX5/6 and PEX7 PEX7 PTS1 is recognized by seven TPR repeats at the contact domain of PEX5 The tetratrico peptide repeat (TPR) is a structural motif of 3-16 tandem-repeats of 34 amino acids residues each. It mediates proteinprotein interactions and the assembly of multi-protein complexes. PTS1: C-terminal tripeptide SKL Stanley et al. (2007) FEBS Lett 581:

12 Protein Import into Peroxisomes Luminal (Matrix) Proteins: Role of Cytosolic Receptors PEX5/6 and PEX7 PTS1 is recognized by seven TPR repeats at the contact domain of PEX5 The tetratrico peptide repeat (TPR) is a structural motif of 3-16 tandem-repeats of 34 amino acids residues each. It mediates proteinprotein interactions and the assembly of multi-protein complexes. Stanley et al. (2007) FEBS Lett 581:

13 Protein Import into Peroxisomes Luminal (Matrix) Proteins: Role of Cytosolic Receptors PEX5/6 and PEX7 W Tryptophan D Aspartic acid PEX7 PTS2 is recognized by a beta-propeller domain (Seven WD40 repeats) at the contact site of PEX7 PTS2: N-terminal alpha-helical motif R(X6)(H/Q)ALF PTS = peroxisomal targeting signal PEX5-PEX7 glyoxysomal receptor PEX6-PEX7 glyoxysomal receptor

14 Protein Import into Peroxisomes Luminal (Matrix) Proteins: Role of Cytosolic Receptors PEX5/6 and PEX7 PTS2 is recognized by a beta-propeller domain (Seven WD40 repeats) at the contact site of PEX7 PTS2 = peroxisomal targeting signal PEX5-PEX7 glyoxysomal receptor PEX6-PEX7 glyoxysomal receptor

15 Protein Import into Peroxisomes Evolutionary Comparison of the PEX Transport Machinery PTS1 PEX5/PEX7 PTS2 BROWN, L-A & BAKER, A (2008) Molec.Membr.Biol. 25(5):

16 Peroxisomes Targeting & Recycling of PEX5 & PEX7 via Mono-Ubiquitination de-ubiquitination poly-ubiquitination followed by protein degradation on 26S proteasomes mono-ubiquitination docking complex RING finger complex * releasing complex RING finger domain Removal of Peroxisomal Targeting Sequences * PEX4 = ubiquitin conjugating enzyme PEX2/12/10 = ubiquitin ligase PEX22=anchoring protein for PEX4 PEX1/6 = ATPase peroxins 15

17 Peroxisomes Proliferation of Peroxisomes/Glyoxysomes 1 pre-peroxisome DLP1 = dynamin-like protein 1 responsible for peroxisomal fission

18 Peroxisomes Nyathi & Baker (2006) Biochimica et Biophysica Acta 1763: Peroxisomal Metabolism Results in Generation of Signalling Molecules ASC: ascorbate DHA: dehydroascorbate GSH: reduced glutathione GSSG: oxidized glutathione GSNO: S-nitroso-glutathione

19 Plastids Elizabeth Gentt unstacked thylakoids stacked thylakoids Structure of the red algal plastid resembles that of Cyanobacteria. In the course of green algal evolution, phycobilisomen were replaced by modern light harvesting complexes containing carotenoids and chlorophyll. Stacking of thylakoid membranes may be seen as an adaptation to low light.

20 Plastids Phycobilisomes in Red Algal Plastids Porphyridium (Rhodophyta) Sitte et al. 1998

21 Accessory Pigments Phycobilins are Light-Capturing Pigments that Pass the Energy to Chlorophylls in the Light Harvesting Complexes of Cyanobacteria and Red Algae Pyrrol PSII

22 Accessory Pigments Phycobilins in the Light Harvesting Complexes of Cyanobacteria and Red Algae Carotenoids in the Light Harvesting Complexes of Green Algae and Land Plants Isopren Pyrrol PSII Beta-Iononring Beta-Iononring 4

23 Plastids

24 Types of Plastids Plastidal Development

25 Types of Plastids

26 Plastids - Amyloplasts ADP-Glucose 1,4-Glycosidic Bonds Starch Grains Linear Amylose (20%) Branched Amylopectin (80%) Carmine acetic acid staining Jodine/Potassium iodid-staining

27 Amyloplast Birefringence a b Maltese Cross Image of Starch in Polarized Light c 1µm d e Wanner 2005 Jiang et al. 2010

28 Glycogen Glycogen is Multibranched Polysaccharide of Glucose UDP-Glucose

29 Compartmentation of Photosynthesis Oxygen Generation CO2 Trace gas 0,038%

30 Compartmentation of Photosynthesis Structure of Chlorohylls individual π-orbitals around C-atoms fuse to single planar orbits above and below the ring structure I II IV III Cyclic Tetrapyrrol Fe as central atom = Heme group Absorptionspectra of Chlorophylls and Carotenoids Chlorophyllid Heme Enzymes: Cytochrome Peroxidase Catalase Leghemoglobin Phytol = Geranylgeraniol (Diterpenderivative) Hemoglobin Isopren

31 Photosynthetic Pigments Reduction of Plastoquinone Primary Electron Donors

32 Photo-Oxidative Damage ROS ROS Excess of Excited Triplet States can Interact with O 2 to Generate Reactive Oxygen Species (O 2- ). ROS can Oxidize Pigments, Lipids and Proteins. Carotins, Ascorbic Acid, Glutathione, Prolin and Thioredoxin: Protect Against ROS.

33 Violaxanthine Cycle Zeaxanthin ZE = zeaxanthin epoxidase VDE = violoxanthin de-epoxidase Violaxanthin Violaxanthine Cycle Controls the Redox-State in Chloroplasts

34 Resonance Energy Transfer One Molecule of Chlorophyll Absorps One Photon and Loses One Electron Proton Gradient is Generated Across Thylakoid Membrane: Its Dissipation is Used by ATP-Synthase to Generate ATP Chemiosmotic Synthesis of ATP Water is Source of Electrons

35 Photosynthesis One Molecule of Chlorophyll Absorps One Photon and Loses One Electron Chlorophyll Molecule Regains Lost Electron from Water Molecule via Photolysis PSII Mediates Oxidation of Water PSI - Mediates Electron Transfer from Plastocyanin to Ferredoxin Electron Transport Chain Provides Energy for Chemiosmotic Synthesis of ATP Water is Source of Electrons 4 H + are Used per ATP

36 Compartmentation of Electron Transport Chain Ferredoxin NADP Oxidoreductase (Fe/S) Plastoquinon- Pool Water splitting complex (Mn/Fe/S) Cytochrom b6f- Complex (Häm-Fe) Plastocyanin (Cu) Thylakoid Lumen Buchanan et al. 2000

37 Proton-Transport ATPase 4 H + per ATP