Next Assignment = GMO plantslab time Friday Mar27 or in class starting March 27 or March 30?•Herbicide resistance• Bromoxynil• Glyphosate (roundup)• Glufosinate (Basta)• Isoxaflutole (Balance, Corvus, Prequel)• Dicamba/2,4-D

•Pathogen/herbivore resistance• BT (Bacillus thuringiensis toxin)• Colorado Potato Beetle (CPB) Resistant NewLeaf Potato• Papaya Ring Spot Virus Resistant Papaya

•Improving nutrition• Golden rice• Potato: reducing acrylamide

•Improving shelf-life• FlavrSavr tomato.

•Making vaccines, other useful biochems

PSI and PSII work together in the “Z-scheme” Light absorbed by PS II makes ATPLight absorbed by PS I makes reducing power

Binding Change mechanism of ATP synthesis1) H+ translocation alters affinity of active site for ATP2) Each active site ratchets through 3 conformations that have different affinities for ATP, ADP & Pi

3) ATP is synthesized by rotational catalysisg subunit rotates as H+ pass through Fo, forces each active site to sequentially adopt the 3 conformations

Evidence supporting chemiosmosis1) ionophores (uncouplers)2) can synthesize ATP if create ∆pH

a) Jagendorf expt: soak cp in pH 4 in dark, make ATP when transfer to pH 8

Evidence supporting chemiosmosisRacker & Stoeckenius (1974) reconstituted bacteriorhodopsin and ATP synthase in liposomesBacteriorhodopsin uses light to pump H+

make ATP onlyin the light

Evidence supporting “rotational catalysis”Sambongi et al experimenta) reconstituted ATPase & attached subunits to a slideb) attached actin filament to c subunit & watched it spin

Regulating Light reactions

Regulate partitioning of light energy between PSI and PSII by phosphorylating LHCII complex

ordinarily is associated with PSII.

Regulating Light reactionsRegulate partitioning of light energy between PSI and PSII by phosphorylating LHCII complex

ordinarily is associated with PSII. if PSI falls behind PSII LHCII is kinased

Regulating Light reactionsif PSI falls behind PSII LHCII is phosphorylatedincreased negative charge forces it out of appressed stacks

Regulating Light reactionsif PSI falls behind PSII LHCII is phosphorylatedincreased negative charge forces it out of appressed stacks it then associates with PSI & boosts PSI cyclic activity

Regulating Light reactionsif PSI falls behind PSII LHCII is phosphorylatedincreased negative charge forces it out of appressed stacks it then associates with PSI & boosts PSI cyclic activity sensor is PQ: when highly reduced it indirectly activates a protein kinase that kinases LHCII

Regulating Light reactionssensor is PQ: when highly reduced it indirectly activates a protein kinase that kinases LHCIIelevated PQH2 means PSI is falling behind

Regulating Light reactionssensor is PQ: when highly reduced it indirectly activates a protein kinase that kinases LHCIIelevated PQH2 means PSI is falling behindAllows plants to adjust relative ATP & NADPH syn

Regulating ATP synthasein dark, ATP synthase couldrun backwards and consumeATP to make a PMF

Regulating ATP synthasein dark, ATP synthase couldrun backwards and consumeATP to make a PMF2 mechanisms prevent this1) ATP synthase needs a pH gradient to be active

Regulating ATP synthasein dark, ATP synthase couldrun backwards and consumeATP to make a PMF2 mechanisms prevent this1) ATP synthase needs a pH gradient to be active2) ATP synthase must be reduced by ferredoxin (via thioredoxin) to be activebecomes oxidized (therefore inactive) in the dark

PhotoinhibitionPhotoinhibition

Most plants are Most plants are saturated at 1/4 full saturated at 1/4 full sunlightsunlight

PhotoinhibitionPhotoinhibition

Most plants are Most plants are saturated at 1/4 full saturated at 1/4 full sunlightsunlightExcess will damage Excess will damage photosystemsphotosystems

PhotoinhibitionPhotoinhibition

Most plants are Most plants are saturated at 1/4 full saturated at 1/4 full sunlightsunlightExcess will damage Excess will damage photosystemsphotosystemsD1 of PSII is fuse: D1 of PSII is fuse: first item to break in first item to break in high lighthigh light

PhotoinhibitionPhotoinhibition

Most plants are Most plants are saturated at 1/4 full saturated at 1/4 full sunlightsunlightExcess will damage Excess will damage photosystemsphotosystemsD1 of PSII is fuse: D1 of PSII is fuse: first item to break in first item to break in high light= high light= photoinhibitionphotoinhibition

PhotoinhibitionPhotoinhibitionD1 of PSII is fuse: D1 of PSII is fuse: first item to break in first item to break in high light= high light= photoinhibitionphotoinhibitionAvoidance?Avoidance?

photoinhibitionphotoinhibitionAvoidance?Avoidance?Carotenoids"quench" excited electronsCarotenoids"quench" excited electrons

photoinhibitionphotoinhibitionAvoidance?Avoidance?Carotenoids"quench" excited electronsCarotenoids"quench" excited electronsDissipate excess energy as heatDissipate excess energy as heat

photoinhibitionphotoinhibitionAvoidance?Avoidance?Carotenoids"quench" excited electronsCarotenoids"quench" excited electronsDissipate excess energy as heatDissipate excess energy as heatViolaxanthin sends exciton to PSViolaxanthin sends exciton to PS

photoinhibitionphotoinhibitionAvoidance?Avoidance?Carotenoids"quench" excited electronsCarotenoids"quench" excited electronsDissipate excess energy as heatDissipate excess energy as heatViolaxanthin sends exciton to PSViolaxanthin sends exciton to PSZeaxanthin dumps energy as heatZeaxanthin dumps energy as heat

photoinhibitionphotoinhibitionViolaxanthin sends exciton to PSViolaxanthin sends exciton to PSZeaxanthin dumps energy as heatZeaxanthin dumps energy as heatConvert Convert Violaxanthin Violaxanthin to Zeaxantin under high lightto Zeaxantin under high light

photoinhibitionphotoinhibitionViolaxanthin sends exciton to PSViolaxanthin sends exciton to PSZeaxanthin dumps energy as heatZeaxanthin dumps energy as heatConvert Convert Violaxanthin Violaxanthin to Zeaxantin under high lightto Zeaxantin under high lightUse NADPH to revert Use NADPH to revert ZeaxanthinZeaxanthin to to Violanthin Violanthin in low in low lightlight

photoinhibitionphotoinhibitionViolaxanthin sends exciton to PSViolaxanthin sends exciton to PSZeaxanthin dumps energy as heatZeaxanthin dumps energy as heatConvert Convert Violaxanthin Violaxanthin to Zeaxantin under high lightto Zeaxantin under high lightRevert Revert ZeaxanthinZeaxanthin to to Violanthin Violanthin in low lightin low lightOther mechs : paraheliotropism, anthocyaninsOther mechs : paraheliotropism, anthocyanins

Photosynthesis in the real worldThe 3 most important factors limiting photosynthesis1. Light2. pCO2

3. Temp