Lecture 4: Adaptions to a low CO2 high O2 world

Question 1

evolution of Rubisco =

Answer 1

• evolved in ANAEROBIC METHANOGENIC ARCHAEA
• WAS used in nucleotide metabolism
• later recruited into photosynthetic CO2-fixation in bacteria

Question 2

rubisco evolved in an __ atmosphere

Answer 2

O2- free

—> rising O2 revealed a problem!

Question 3

Rubsico’s issue w O2

Answer 3

trouble distinguishing O2 and CO2 = 2 problems

• -> Oxygenation competes with carboxylation (reducing efficiency of photosynthesis)
• -> Oxygenation generates a toxic product, 2-PGA

Question 4

rubiscos problem with O2: photosynthetic organisms strategies to cope =

Answer 4

1) photorespiration –> gets rid of 2-PGA but needs ATP and releases NH3 & CO2
2) carbon-concentrating mechanisms concentrate CO2 at rubiscos active site. Requires energy. (CCMs)

Question 5

CCMs mechanism

Answer 5

• compartment containing rubisco

- pump CO2 using active pump (requires energy i,e, ATP) into site to concentrate CO2 around active site

Question 6

Phanerozoic=

Answer 6

last 600 million years

- at 300mya = giant insects (drop in CO2, increase in O2), serious O2 drop after this

Question 7

problems of rubisco are worse at ___ temperatures

Answer 7

at high temperatures

• 2 reasons why
• –both gases become less soluble at higher temps (gas leaves liquid) WORSE for CO2

— specificity of rubisco (its ability to tell apart CO2 and O2) is worse at high temperatures

Question 8

problems for rubisco are worse in ___ habitats

Answer 8

AQUATIC

• • diffusion of CO2 is ~100 times slower in water than air
• • main supply of CO2 is from HCO3- and chem equilibrium is SLOW
• • total inorganic carbon conc is sensitive to pH –> less abundant in acidic conditions

Question 9

photorespiration when did it evolve?

Answer 9

1- Becker 2013 During snowball (CO2 fell, O2 increased) earth event green plants separated Chlorophyta (green marine algae) and Streptophyta (freshwater algae and land plants) both individually evolved photorespiration as a result of diff ecologies

2- deeper origin (more accepted) once in ancestor and modified later on Hagemann et al 2016

Question 10

evolutions of CCMs

Answer 10

evolved many times in many groups

1) cyanobacteria
2) eukaryotic algae
3) C4 photosynthesis
4) CAM

–> A lot of focus in trying to get CCM’s into C3 Crop plants (all they have is photorespiration NOT CCM at the moment)

Question 11

how did Cenozoic global change drive CCM evolution in land plants?

Answer 11

2 major intervals of low CO2, high O2, glaciation, dry climates

• –Permo-carboniferous (300mya)
• –Oligocene to present (ice on Antarctica) (30mya)

Question 12

glaciations link to ___ CO2

Answer 12

LOW

Question 13

C4 photosynthesis evolution

Answer 13

• evolved more than 70 times
• around half of all living C4 species are grasses
• dominate tropical savannas
• important crops and biofuels

Question 14

C4 photosynthesis mechanism =

Answer 14

• in bundle sheath cell CO2 is concentrated to favour carboxylation over oxygenation (minimising photorespiration)
• saturates Rubisco with CO2 at low CO2 atmospheric CO2 levels
• carries energy cost
• C4 most beneficial at high temp, low CO2 atmospheric conc

Question 15

-C4 most beneficial at

Answer 15

high temp, low CO2 atmospheric conc

Question 16

C4 photosynthesis evolved from

Answer 16

Oligocene-present

–No evidence found for it in Permo-carboniferous

Question 17

C4 photosynthesis evolves in a __ CO2, __ World

Answer 17

low CO2, dry world

Question 18

ice world is a dry world

Answer 18

• last 30 million years,
• tectonic plate movements mountain building,
• causing chem weathering,
• drawn down CO2,
• causing global cooling,
• increase in ice sheet growth,
• lock up free water so DRY

Question 19

C4 photosynthesis evolved in __ climate regions and in ___ habitats

Answer 19

tropical climate regions and in open (unshaded) habitats –> lots of energy!
(know this from looking at phylogeny)

Question 20

C4 photosynthesis enabled lineages to migrate__ & adapt __

Answer 20

• more rapidly from hot lowland tropics into cooler climate regions
• • enabled lineages to adapt faster to arid conditions

Question 21

CAM evolution

Answer 21

• evolved as water-conserving mechanism in a low CO2 world
• closely associated with succulence
• thought to evolve in xeric/arid environments
• 15-20mya diversity expanded

Question 22

falling atmospheric CO2 drove evolution of

Answer 22

CCMs across multiple lineages of bacteria. eukaryotic algae and land plants