Light reaction. Dark reaction

Transcription

1 Photosynthesis

2

3 Light reaction Dark reaction

4

5

6

7 Electro-magnetic irradiance and sunlight

8 CO 2 and O 2 fixation by Rubisco

9 Oxygenic photosynthesis was established in Cyanobacteria

10

11

12

13

14 Localisation of the photosynthetic apparatus - Cell organelles, chloproplasts chloroplasts/cell - endocytobiosis - chloroplasts have two outer membranes with different origin (lipids, proteins) - thylakoids derive from inner (procaryotic) membrane - grana- and stroma thylakoids -new compartment: lumen vs. stroma - different transport processes for proteins into the two plastid compartments -photosynthesis in thylakoid membranes - different association of proteins at the thylakoid membrane

15 Chlorophyll, carotinoid, phycobilin

16 Chlorophyll a

17

18

19

20 Chlorophyll, carotinoid, phycobilin

21

22

23

24 HPLC (high performance liquid chromatography)

25

26 Carotenoids have two functions: - light absorbance - protection against excess light

27 Energy dissipation by xanthophylls Low light = Violaxanthin is present in and around PSII High light = Zeaxanthin synthesis in and around PSII

28 In response to high light, plants have evolved photo protection mechanisms to dissipate the excess absorbed light energy and thus avoid damages to the photosynthetic apparatus. One of the mechanisms is through transfer of the absorbed energy from chlorophyll a to xanthophyll pigment zeaxanthin since excited zeaxanthin decays to the ground level much more rapidly than excited chlorophyll a. Under excessive light condition, violaxanthin is converted to zeaxanthin in the xanthophyll cycle, and thus accelerates the energy dissipation from excited chlorophyll a to zeaxanthin.

29

30 Lemna minor: transfer of green turions to Norflurazon blocks carotenoid biosynthesis: Newly formed turions are white due to photo-oxidative destruction of the entire chloroplasts

31 Chlorophyll, carotinoid, phycobilin Absorption spektrum of phycoerythrin

32

33

34 Phycoerythrin, 545 nm Phycocyanin, 615 nm Allophycocyanin, 650 nm

35

36 Chromatic Adaptation Fremyella diplosiphon

37 Northern Hybridisation

38 Organisation of light harvesting complexes in higher plants

39 Most of the chlorophylls and carotenoids are organized in light-harvesting complexes of the photosystems I and II

40 Chl a and b (and carotenoids) not covalently bound to light-harvesting proteins of antenna Stable antenna for the photosystems I and II Mobile antenna migrates between photosystems Pigments are also bound to the two photosystems -inner antenna - reaction center pigmnents -Light harvesting proteins are encoded by multigene families -Specificity for the two photosystems -Phyologenetic analyses -Early light-induced proteins (ELIPs)

41

42 Crystal structure of the light harvesting antenna of PSII

43

44 Mutants in photosynthesis Light is absorbed by antenna and emited as fluorescence hcf (high chlorophyll fluorescence) phenotype

45

46 PSII und PSI wird durch unterschiedliches Licht angeregt: Erzeugung von Redoxsignalen

47 Redox-Signale steuern plastidäre und nukleäre Ereignisse

48

49 Adaptation to unbalanced excitation of PSII and PSI (1) state transition (fast): relocation of mobile antenna (2) change in plastid gene expression: genes for limiting PS complex are upregulated (3) change in nuclear gene expression

50 More PSII excitation > PSI activity is limiting Phosphorylation of mobile antenna migration to PS I

51

52

53

54 Plastid localisation of a protein Comparison of chlorophyllautofluorescence (indicator for plastids, red chlorophyll fluorescence) with green fluorescence protein (tag on protein)

55 The four photosynthetic complexes Photosystem II Cytochrom b6/f -complex Photosystem I ATP-synthase

56

57

58 In eukaryotic organism: thylakoid proteins are of dual genetic origin

59 Structural information of the thylakoid complexes requires purification Photosystem I

60 Photosynthetic complexes contain - membrane integral proteins (e.g. D1) - stroma-exposed proteins - lumen-exposed proteins (different sorting mechanisms)

61

62 PS I can be purified from thylakoid membranes Identification of the protein composition by onedimensional gel electrophoresis

63 The ATP synthase has a membrane-integral F 0 part and a stroma-exposed F 1 part

64

65

66 Chloroplasts derive from symbiotic events primary secondary tertiary symbiosis

67 Arabidopsis is a model system for plant physiologists

68

69 Arabidopsis thaliana complete genome sequenced microarrays proteomics knock-out lines for almost all genes available transformation techniques are available genetics is easy to perform generation time is short (3 months) small plant (easy to grow and cultivate)

70

71 Protochlorophyllide oxidoreductase (POR) The key enzyme for greening in angiosperms Etioplasts: prolamellar body Storage for POR and protochlorophyllide light-activated enyzme Light: photoconversion of protochlorophyllide to chlorophyllide Pinus: POR is not light-activated Greening in the dark Similarities to phytochrome function

72 Biosynthesis of chlorophylls - starts with glutamate - porphyrin - tetrapyrrole

73

74

75 Immunolokalisation

76