1. Energy acquisition and biochemical pathways: Photosynthetic pathways (C 3, C 4, CAM)

2. Questions Lectures now posted on wiki Discussions: – Mariana: posting paper and questions for this week – Dilys: will be picking a paper to post for next week Any questions?

3. Ferns Gymnosperms Angiosperms

4. Carbon dioxide uptake by plants CO 2 is –About 0.038% in atmosphere –What about inside leaves? –But remember CO 2 uptake is in exchange for H 2 O loss. What about differences in water across the leaf surface?

6. What is photosynthesis?

7. RUBISCO RUBISCO, drives –Carbon fixation in photosynthesis and releases oxygen (but has a low affinity for CO 2 ), –Carbon release in photorespiration with oxygen as substrate.

8. RuBP + CO 2  2PGA Photosynthesis Photorespiration RuBP + O 2  glycolate Photorespiration: No carbon fixed but glycolate can be used in amino acid synthesis

9. Photosynthetic strategies Most plants (C 3 ): fix carbon dioxide initially as phosphoglycerate (PGA), a three-carbon compound. –Enzyme is ribulose bi-phosphate carboxylase- oxidase (RUBISCO) –Biochemical cycle is called Calvin cycle.

11. But, if it is really hot and dry water uptake is a problem. What to do?

12. Hatch and Slack cycle Some plants, mainly tropical grasses, C 4 : first combine carbon dioxide with phospho-enol- pyruvate (PEP), into a four carbon compound – oxaloacetate.

15. Crassulacean Acid Metabolism (CAM) Third photosynthetic strategy (CAM): first found in plants in the family Crassulaceae and was therefore called Crassulacean Acid Metabolism. Plants in other families also use this mode of carbon fixation (lots of succulents and epiphytes).

18. What do you think the main advantages and disadvantages of each strategy is?

19. Evolution of C 4 in grasses

20. Question Why did C 4 evolve in grasses? – Dogma: A response to rising temperatures and lowering CO 2 – To test this, for 1230 grass spp, 1.1 million specimens GBIF: georeference points Climate: CRU (Climate Resource Unit) DNA sequences: With PHLAWD, built a phylogeny – Chloroplast regions: atpB (59 taxa), matK (266 taxa), ndhF (437 taxa), rbcL (251 taxa), rpl16 (176 taxa), and trnL-trnF (810 taxa) – Nuclear regions: phyB (93 taxa) and the internal transcribed spacer (ITS; 753 taxa)

21. Ferns Gymnosperms Angiosperms

22. PoalesPoaceae

23. Shady

29. Question Why did C 4 evolve in grasses? – Forget dogma: Grasses were historically warm adapted C 4 evolution was in response to a drop in precipitation So, the shift was probably from tropical rainforests understories to open tropical savannahs and grasslands!!! The question then becomes, when, why, and how did C 3 grasses evolve cold tolerance?