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Plant defense responses Hypersensitive response Systemic acquired resistance Innate immunity

Prepare a 10 ’ talk for Friday March 3 on plant defense responses or describe interactions between plants& pathogens, pests or symbionts. Plant defense responses Hypersensitive response Systemic acquired resistance Innate immunity Phytoalexin synthesis Defensins and other proteins

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Plant defense responses Hypersensitive response Systemic acquired resistance Innate immunity

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  1. Prepare a 10’ talk for Friday March 3 on plant defense responses or describe interactions between plants& pathogens, pests or symbionts Plant defense responses • Hypersensitive response • Systemic acquired resistance • Innate immunity • Phytoalexin synthesis • Defensins and other proteins • Oxidative burst Some possible pests • Nematodes • Rootworms • Aphids • Thrips • Gypsy moths • hemlock woolly adelgid Some possible pathogens • Agrobacterium tumefaciens • Agrobacterium rhizogenes • Pseudomonas syringeae • Pseudomonas aeruginosa • Viroids • DNA viruses • RNA viruses • Fungi • Oomycetes Some possible symbionts • N-fixing bacteria • N-fixing cyanobacteria • Endomycorrhizae • Ectomycorrhizae

  2. Photosynthesis 2 sets of rxns in separate parts of chloroplast

  3. Light-independent (dark) reactions Overall Reaction: 3 CO2 + 3 RuBP + 9 ATP + 6 NADPH = 3 RuBP + 9 ADP + 9 Pi + 6 NADP+ + 1 Glyceraldehyde 3-P

  4. Light-independent (dark) reactions 1) fixing CO2 2) reversing glycolysis 3) regenerating RuBP

  5. fixing CO2 1) RuBP binds CO2

  6. fixing CO2 • 1) CO2 is bound to RuBP • 2) rapidly splits into two 3-Phosphoglycerate • therefore called C3 photosynthesis • detected by immediately killing cells fed 14CO2

  7. fixing CO2 • 1) CO2 is bound to RuBP • 2) rapidly splits into two 3-Phosphoglycerate • 3) catalyzed by Rubisco (ribulose 1,5 bisphosphate carboxylase/oxygenase) • the most important & abundant protein on earth • Lousy Km • Rotten Vmax! • Makes lots of mistakes!

  8. Reversing glycolysis converts 3-Phosphoglycerate to G3P consumes 1 ATP & 1 NADPH

  9. Reversing glycolysis • G3P has 2 possible fates • 1) 1 in 6 becomes (CH2O)n

  10. Reversing glycolysis • G3P has 2 possible fates • 1) 1 in 6 becomes (CH2O)n • 2) 5 in 6 regenerate RuBP

  11. Reversing glycolysis 1 in 6 G3P becomes (CH2O)n either becomes starch in chloroplast (to store in cell)

  12. Reversing glycolysis 1 in 6 G3P becomes (CH2O)n either becomes starch in chloroplast (to store in cell) or is converted to DHAP & exported to cytoplasm to make sucrose

  13. Reversing glycolysis 1 in 6 G3P becomes (CH2O)n either becomes starch in chloroplast (to store in cell) or is converted to DHAP & exported to cytoplasm to make sucrose Pi/triosePO4 antiporter only trades DHAP for Pi

  14. Reversing glycolysis 1 in 6 G3P becomes (CH2O)n either becomes starch in chloroplast (to store in cell) or is converted to DHAP & exported to cytoplasm to make sucrose Pi/triosePO4 antiporter only trades DHAP for Pi mechanism to regulate PS

  15. Regenerating RuBP • G3P has 2 possible fates • 5 in 6 regenerate RuBP • necessary to keep cycle going

  16. Regenerating RuBP Basic problem: converting a 3C to a 5C compound feed in five3C sugars, recover three5C sugars

  17. Regenerating RuBP Basic problem: converting a 3C to a 5C compound must assemble intermediates that can be broken into 5 C sugars after adding 3C subunit

  18. Regenerating RuBP making intermediates that can be broken into 5 C sugars after adding 3C subunits 3C + 3C + 3C = 5C + 4C

  19. Regenerating RuBP making intermediates that can be broken into 5 C sugars after adding 3C subunits 3C + 3C + 3C = 5C + 4C 4C + 3C = 7C

  20. Regenerating RuBP making intermediates that can be broken into 5 C sugars after adding 3C subunits 3C + 3C + 3C = 5C + 4C 4C + 3C = 7C 7C + 3C = 5C + 5C

  21. Regenerating RuBP making intermediates that can be broken into 5 C sugars after adding 3C subunits 3C + 3C + 3C = 5C + 4C 4C + 3C = 7C 7C + 3C = 5C + 5C Uses 1 ATP/RuBP

  22. Light-independent (dark) reactions build up pools of intermediates , occasionally remove one very complicated book-keeping

  23. Light-independent (dark) reactions build up pools of intermediates , occasionally remove one very complicated book-keeping Use 12 NADPH and 18 ATP to make one 6C sugar

  24. Regulating the Calvin Cycle Rubisco is main rate-limiting step

  25. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • indirectly regulated by light 2 ways • 1) Rubiscoactivase: Rubisco must be carbamylated & bind Mg2+ to be active!

  26. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • indirectly regulated by light 2 ways • 1) Rubisco activase : • uses ATP to activate rubisco

  27. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • Rubisco must be carbamylated & bind Mg2+ to be active! • RuBP binds & inactivates uncarbamylatedrubisco • Rubiscoactivase removes this RuBP

  28. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • Rubisco must be carbamylated & bind Mg2+ to be active! • RuBP binds & inactivates uncarbamylatedrubisco • Rubiscoactivase removes this RuBP • In the dark many species phosphorylate carboxyarabinotol to form carboxyarabinitol 1-phosphate which binds the rubisco active site

  29. Regulating the Calvin Cycle • Rubiscoactivase removes this RuBP • In the dark many species phosphorylate carboxyarabinotol to form carboxyarabinitol 1-phosphate which binds the rubisco active site • Rubiscoactivase also removes CA1P in the light • CA1P phosphatase then removes the PO4

  30. Regulating the Calvin Cycle Availability of CO2 Demand is set by mesophyll, stomata control supply Ci is usually much lower than Ca A vsCi plots tattle on the Calvin cycle

  31. Regulating the Calvin Cycle A vsCi plots tattle on the Calvin cycle • In linear phase rubisco is limiting • When curves RuBP or Pi regeneration is limiting

  32. Regulating the Calvin Cycle Currently Rubisco usually limits C3 plants Will increase plant growth until hit new limiting factor

  33. Regulating the Calvin Cycle Currently Rubisco usually limits C3 plants Will increase plant growth until hit new limiting factor Free-Air CO2 Enrichment Experiments show initial gains, but taper off w/in a few years Now are limited by nutrients or water

  34. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • indirectly regulated by light 2 ways • 1) Rubisco activase • 2) Light-induced changes in stroma

  35. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • indirectly regulated by light 2 ways • 1) Rubisco activase • 2) Light-induced changes in stroma • a) pH: rubisco is most active at pH > 8 • (in dark pH is ~7.2)

  36. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • indirectly regulated by light 2 ways • 1) Rubisco activase • 2) Light-induced changes in stroma • a) pH: rubisco is most active at pH > 8 • b) [Mg2+]: in light [Mg2+] in stroma is ~ 10x greater than in dark

  37. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • indirectly regulated by light 2 ways • 1) Rubisco activase • 2) Light-induced changes in stroma • a) pH: rubisco is most active at pH > 8 • b) [Mg2+]: in light [Mg2+] in stroma is ~ 10x greater than in dark • Mg2+ moves from thylakoid lumen to stroma to maintain charge neutrality

  38. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • indirectly regulated by light 2 ways • 1) Rubisco activase • 2) Light-induced changes in stroma • a) pH: rubisco is most active at pH > 8 • b) [Mg2+]: in light [Mg2+] in stroma is ~ 10x greater than in dark • c) CO2 is an allosteric activator of rubisco that only binds at high pH and high [Mg2+] • also: stomates open in the light

  39. Regulating the Calvin Cycle • Rubisco is main rate-limiting step • indirectly regulated by light 2 ways • 1) Rubisco activase • 2) Light-induced changes in stroma • Several other Calvin cycle enzymes (e.g.Fructose-1,6-bisphosphatase) are also activated by high pH & [Mg2+]

  40. Regulating the Calvin Cycle • Several Calvin cycle enzymes (e.g.Fructose-1,6-bisphosphatase) are also regulated by thioredoxin • contain disulfide bonds which get oxidized in the dark

  41. SH SH light oxidized enzyme (inactive) S - S reduced thioredoxin 2Fdox 2e- PSI + PSII S - S SH SH oxidized thioredoxin reduced enzyme (active) 2Fdred • Regulating the Calvin Cycle • Several Calvin cycle enzymes (e.g.Fructose-1,6-bisphosphatase) are also regulated by thioredoxin • contain disulfide bonds which get oxidized in the dark • in light, ferredoxin reduces thioredoxin, thioredoxin reduces these disulfide bonds to activate the enzyme

  42. Regulating the Calvin Cycle • Several Calvin cycle enzymes (e.g.Fructose-1,6-bisphosphatase) are also regulated by thioredoxin • contain disulfide bonds which get oxidized in the dark • in light, ferredoxin reduces thioredoxin, thioredoxin reduces these disulfide bonds to activate the enzyme • How light reactions talk to the Calvin cycle SH SH light oxidized enzyme (inactive) S - S reduced thioredoxin 2Fdox 2e- PSI + PSII S - S SH SH oxidized thioredoxin reduced enzyme (active) 2Fdred

  43. PHOTORESPIRATION Rubisco can use O2 as substrate instead of CO2 RuBP + O2 <=> 3-phosphoglycerate + phosphoglycolate

  44. PHOTORESPIRATION Rubisco can use O2 as substrate instead of CO2 RuBP + O2 <=> 3-phosphoglycerate + Phosphoglycolate Releases CO2 without making ATP or NADH

  45. PHOTORESPIRATION • Releases CO2 without making ATP or NADH • Called photorespiration : undoes photosynthesis

  46. PHOTORESPIRATION Rubisco can use O2 as substrate instead of CO2 RuBP + O2 <=> 3-phosphoglycerate + Phosphoglycolate C3 plants can lose 25%-50% of their fixed carbon

  47. PHOTORESPIRATION Rubisco can use O2 as substrate instead of CO2 RuBP + O2 <=> 3-phosphoglycerate + Phosphoglycolate C3 plants can lose 25%-50% of their fixed carbon Both rxns occur at same active site

  48. PHOTORESPIRATION C3 plants can lose 25%-50% of their fixed carbon phosphoglycolate is converted to glycolate : poison!

  49. Detoxifying Glycolate 1) glycolate is shuttled to peroxisomes

  50. Detoxifying Glycolate • 1) glycolate is shuttled to peroxisomes • 2) peroxisomes convert it to glycine • produce H2O2

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