VL 2

1. regulation by light in the plasid

2. (metabolic) interaction of the plastid with other components

3. gene regulation (“crosstalk”) bewteen nucleus and chloroplast

4. regulation of photoreceptors

• many biosynthetic pathways need regulation:

  • CO2 fixation (Calvin cycle)

  • sulfate reduction

  • synthesis of pigments

  • gene expression in the plastid

  • translation of proteins

• small redox proteins

• are ubiquitous (from prokarytotes to plants and animals)

• at the N-Terminus a WCGPC is present, which is responsible for redox-regulation

• tertiary structure and redox potential are decisive for the substrate specificity

• regulation works by forming and cleaving of the disulfide bride (cytsine formation)

• cyle depends on the redox state of the electron transport chain

  > or redox state of ferrodoxin

• RubisCo-activase removes (ATP dependent) CA1P

• by this carbomylation of the avtive centre becomes possible

• formation of a complex with Mg2+

• feedback inhibition and allosteric regulation

• glutathione/glutathionylation (like Tx)

• reversible (lysin)-acetylation (especially for enyzmes)

• during day:

  • starch: synthesized and stored in the chloroplast

  • sucrose: sythesized in the cytosol from triose-P, which originates from the plastid, transport in other tissued for storage

• during night:

  • consumption of the stores carbohydeates in the chloroplast and elsewhere

• 3-phosphoglycerate and triose-P and the main metabolites in the chloroplast

• 5/6 of the pool are needed for regenration pf ribulose-1,5-bisphosphate in the Clavin cyle

• further losses by photorespiration

• only 1/8 of the pool is exported

  > no more export allowed, since otherwise lack of P in the plastid

  > too little export not allowed, since otherwise lack of P in the plastid

• high amounts of triose-P or high consumption of sucrose:

  stron sucrose synthesis

  > sufficient use of triose-P is guranteed

• triose-P/Pi - translocator:

  if no sucrose synthesis possible, no Pi import into chloroplst, no further triode-P-export

  > perfect adjustment of triose-P export

if no sucrose sythesis possible, no import into chloroplast no further triose-P export

> perfect adjustment of triose-P export

> starch as buffer for the phosphate pool

• nitrate and nitrite reducton have to be synchonised (prevention of toxic nitrite)

• nitrate reduction is turned off in the leaf darkness (becuase nitrite reduction and following reactions depend on Fd, NADPH and ATP photosynthesis)

• light, nitrate and glucose induce gene expression of nitrate reductase, glutamine inhibits

• regulation of enzyme activity:

  phosphoryltaion folllowed by binding of an inhibitory protein inactivates, kinase inhibited by triose-P (produced in the light by the plastid), i.e. light inhibits via triose-P, in darkness inhibition can occur

• from nucleus to chloroplast

• triggered by e.g. photoreceptors or circadian clock

• from plastid to nucleus

• transmit informationabout the development state of the plastid (biogenic signals)

• transmit information about the photosynthesis and metabolism(operation signal)

1. intermediateof chlorophyll (tetrapyrrol)-synthesis, mainly Mg-Protoporphyrin-IC

2. other metabolites

3. plastidic gene expression

4. plastidic transcription factors

5. ROS

6. redox signals

• gene expression two genomes has to be regulated (e.g. genes for PSII (lastidic) with LHC (nuclear encoded))

• chlorophyll synthesis intermediates (from Mg-protoporphyrin IX onwards) are phototoxic

• if chlorophyll/photosystem assembly is disturbed, the plastid sends a signal, mainly via GUN1 and Mg-protoporphyrin IX, to switch off nuclear photosynthesis genes (PhANGs) through factors like ABI4/HY5

• no D1-synthesis:

  Gum1 inhibits psbO- and LHCII-mRNA synthesis in the nucleus (via PTM and ABI4)

• d1-synthesis,but no assembly (no use of CHl a) > Mg-protoprphyrin IX inibits

• UVR8: UV, about 300–350 nm.

• BLUF receptor: about 320–500 nm.

• Cryptochrome: about 350–500 nm.

• Aureochrome: about 350–550 nm.

• Phototropin / Zeitlupe: about 350–550 nm.

• Rhodopsin: about 450–600 nm.

• Phytochrome: about 600–800 nm.

• light absorption induces cellulae changes

  > change of transcription

  > change of membane potential (e.g. opening stomata

• UV receptor, reception via tryptophan

• many photomorphogenetic reactions

• dimeric, monomerisation after absorpton

• monomer interacts with COP1

• soluble protein with a nuclear import domain (inside PASdomian)

• absorption of red light leads to Pfr (active form)

• absorption of far-red light leads to Pr (inactive form)

• chromophore. phytochromobilin (inear tetrapyrolle)

• histii kinase relateddomain (HKRD) = classical effector domain, but specifity unclear

• active form (PFR) ins to transcription factors

> gene regulation

phyA

• photomorgenesis and light dependent of etilated seedlings

• phyB: light dependent germinatin

• phyC: photomorphogenesis of seedlings in light

• phyD

• phyE: photoperdicaly nduceddevelopment (e.g. flower induction)

• bin flavin-chromophore > blue light sensor

• phototrophin/zeitluoe/auerochrome

• here only phototropin (phot1/phot2)

  • membrane proteins

  • LOV- and effector domain (ser-Thr kinase)

  • responsible for stomatal opening, chloroplast movement, phototropisn

• because FAD binding blue light receptor, often “antenna chromophore” in addition

• membersof the cryptochrome/photolysae family

• photolysase homologue region (PHR) and C-terminal extension (CCT)

• soluble protein

• photolysases: CPD and 6-4

• cryptochrome: animal/plant/DASH

• photolyasesand CRY very similar

• FAD and second chromophore, mostlyMTHF or HDF

• MTHF as antenna chrmophore

• here: FADH* bound, oxidises by time. in the dark FAD

• BL- (and UV) - absorption, mainly MTHF

Cryptochromes (CRY1/CRY2): in the dark they are inactive; blue light activates them by phosphorylation, then they form a signaling complex with COP1/SPA, which stabilizes HY5 and triggers de-etiolation and flowering.

• light-induced auto-phosphorylation at CTE (also calles CCE)

• incease of HY5 content by inhibition of its degradation

• gene expressio