Lecture 4: C4 plants, advantages and origins Flashcards
In c4 plants CO2 is ___ around Rubisco in the ____, supressing
CO
2 is concentrated around
Rubisco in the bundle‐sheath,
suppressing photorespiration
C4 plants contain two key types of different cells
- mesophyll cells
- wreath (Kranz) of bundle-sheath cells
concentration difference between normal cells and cells surrounding Rubisco is increased by
10 fold
100 ppm CO2 compared to 1000 ppm CO2
Increasing temperatures affect on photorespiration
Increases
temperature dependence of photosynthesis in two grasses - one C3 and other C4
C3: -optimum temperature ~25 degrees C - 25+ photorespiration increases C4: -optimum at ~40-45 degrees
Cross-over at 25-30 degrees
distribution of C4 grasses in North America
> 60% at southern North America = more where higher temperatures
distribution of C4 grasses in Australia
> 90% in northern Australia.
higher % in higher temperatures
C4 abundance on the slopes of mount kenya
- Higher altitudes have lower temperatures and higher rainfall
- % C4 species =
- 100% at lower elavations (~0-1900 m)
- dropping to 0% species at 3000m - 4000m
C4 leaves operate at ___ intercellular CO2 concentrations , and are capable of…
LOWER
capable of high photosynthesis at low CO2 because they concentrate CO2
C4 plants supress
photorespiration
stomatal conductance at fixed CO2 uptake of 30 comparing C3 and C4
C4 = ~160 C3 = ~ 390. C3 = more open stomata = greater loss of water
In C3 plants Rubisco comprises about __% of leaf soluble protein & is involved in …
50%
photorespiration.
By supressing photorespiration, C4 plants use Rubisco more productively
C4 and C3 plants and biomass
C4 plants produce more biomass in same amount of time as C3
C4 plants at higher temperatures:
C4 crop shave increased yield and reduced demand for inputs compared to C3 species
C4 plants have improved:
• CO2 fixation • Water‐use efficiency • Nitrogen‐use efficiency • Light‐use efficiency Could it be engineered into C3 crops?
Carbon isotope discrimination can be used to
distinguish between C3 and C4 plants
there are two forms of CO2 in the atmosphere:
12CO2 (98.89%)
13CO2 (1.11%)
Different physical and chemical processes ____ against 13CO2 to different degrees
discriminate
discrimination of 13CO2 is measured in
parts per thousand against a standard belemnite limestone
delta13C in atmosphere is
-7 parts per thousand
if the product has a delta13C of -27 parts per thousand then fractionation is
+20 parts per thousand
delta13C fractionation (parts per thousand) for
- diffusion
- PEP carboxylase
- Rubisco
- diffusion = + 4
- PEP carboxylase = +2
- Rubisco = + 34
• Rubisco discriminates against 13CO2 to a much greater degree
than PEP carboxylase
C3 plant carbon isotope Sugar.
C3 plant +CO2
–> Rubisco –> products.
Delta13C -25 to 35 parts per thousand
C4 plant carbon isotope sugar
C4 plant +CO2 –> PEP carboxylase –> Rubisco –> products
Delta13C -10 to -17 parts per thousand
C4 evolved in the last ___ in response to
C4 evolved in the last 25‐30 million years in response to decreased atmospheric CO2 concentration
Fossil horses and C4 plants
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
expansion of C4 ecosystems occurred
6-8 million years ago
C4 plants originated…
separately many times
phylogenetic indicates at least __
66 separates origins of C4 pathway
C4 pathway evolved independently in
19 families go higher plants
origin of C4 plants:even within a single genus there are
are all three biochemical subtypes, suggesting separate origins.
