Lecture 4: C4 plants, advantages and origins

Question 1

In c4 plants CO2 is ___ around Rubisco in the ____, supressing

Answer 1

CO
2 is concentrated around
Rubisco in the bundle‐sheath,
suppressing photorespiration

Question 2

C4 plants contain two key types of different cells

Answer 2

• mesophyll cells

- wreath (Kranz) of bundle-sheath cells

Question 3

concentration difference between normal cells and cells surrounding Rubisco is increased by

Answer 3

10 fold

100 ppm CO2 compared to 1000 ppm CO2

Question 4

Increasing temperatures affect on photorespiration

Answer 4

Increases

Question 5

temperature dependence of photosynthesis in two grasses - one C3 and other C4

Answer 5

C3:
-optimum temperature ~25 degrees C 
- 25+ photorespiration increases 
C4: 
-optimum at ~40-45 degrees 

Cross-over at 25-30 degrees

Question 6

distribution of C4 grasses in North America

Answer 6

> 60% at southern North America = more where higher temperatures

Question 7

distribution of C4 grasses in Australia

Answer 7

> 90% in northern Australia.

higher % in higher temperatures

Question 8

C4 abundance on the slopes of mount kenya

Answer 8

• Higher altitudes have lower temperatures and higher rainfall
• % C4 species =
• • 100% at lower elavations (~0-1900 m)
• • dropping to 0% species at 3000m - 4000m

Question 9

C4 leaves operate at ___ intercellular CO2 concentrations , and are capable of…

Answer 9

LOWER

capable of high photosynthesis at low CO2 because they concentrate CO2

Question 10

C4 plants supress

Answer 10

photorespiration

Question 11

stomatal conductance at fixed CO2 uptake of 30 comparing C3 and C4

Answer 11

C4 = ~160 
C3 = ~ 390. 
C3 = more open stomata = greater loss of water

Question 12

In C3 plants Rubisco comprises about __% of leaf soluble protein & is involved in …

Answer 12

50%
photorespiration.
By supressing photorespiration, C4 plants use Rubisco more productively

Question 13

C4 and C3 plants and biomass

Answer 13

C4 plants produce more biomass in same amount of time as C3

Question 14

C4 plants at higher temperatures:

Answer 14

C4 crop shave increased yield and reduced demand for inputs compared to C3 species

Question 15

C4 plants have improved:

Answer 15

• CO2 fixation
• Water‐use efficiency
• Nitrogen‐use efficiency
• Light‐use efficiency
Could it be engineered into C3 crops?

Question 16

Carbon isotope discrimination can be used to

Answer 16

distinguish between C3 and C4 plants

Question 17

there are two forms of CO2 in the atmosphere:

Answer 17

12CO2 (98.89%)

13CO2 (1.11%)

Question 18

Different physical and chemical processes ____ against 13CO2 to different degrees

Answer 18

discriminate

Question 19

discrimination of 13CO2 is measured in

Answer 19

parts per thousand against a standard belemnite limestone

Question 20

delta13C in atmosphere is

Answer 20

-7 parts per thousand

Question 21

if the product has a delta13C of -27 parts per thousand then fractionation is

Answer 21

+20 parts per thousand

Question 22

delta13C fractionation (parts per thousand) for

• diffusion
• PEP carboxylase
• Rubisco

Answer 22

• diffusion = + 4
• PEP carboxylase = +2
• Rubisco = + 34

• Rubisco discriminates against 13CO2 to a much greater degree
than PEP carboxylase

Question 23

C3 plant carbon isotope Sugar.

Answer 23

C3 plant +CO2
–> Rubisco –> products.

Delta13C -25 to 35 parts per thousand

Question 24

C4 plant carbon isotope sugar

Answer 24

C4 plant +CO2 –> PEP carboxylase –> Rubisco –> products

Delta13C -10 to -17 parts per thousand

Question 25

C4 evolved in the last ___ in response to

Answer 25

C4 evolved in the last 25‐30 million years in response to decreased atmospheric CO2 concentration

Question 26

Fossil horses and C4 plants

Answer 26

look at mammalian tooth enamel. looking at >8 MYR tooth enamel can see no record of C4 as no C4 dominated diet. Is present in modern tooth enamel

Question 27

expansion of C4 ecosystems occurred

Answer 27

6-8 million years ago

Question 28

C4 plants originated…

Answer 28

separately many times

Question 29

phylogenetic indicates at least __

Answer 29

66 separates origins of C4 pathway

Question 30

C4 pathway evolved independently in

Answer 30

19 families go higher plants

Question 31

origin of C4 plants:even within a single genus there are

Answer 31

are all three biochemical subtypes, suggesting separate origins.