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Photorespiration
Photosynthesis
6CO2 + 6H2O
C6H12O6 + 6O2
Respiration (mitochondrial respiration)
C6H12O6 + 6O2
6CO2 + 6H2O
Photorespiration
C6H12O6 + 6O2
6CO2 + 6H2O
Sunflower leaves
The relative rate of photosynthesis
is a function of temperature.
Hew, Krotkov, Canvin, Plant Physiol 44:671, 1969
The relative rate of photosynthesis is a
function of temperature.
The relative rate of photosynthesis is a
function of temperature.
Why is Rubisco called a “carboxylase-oxygenase?
- Alternative activity at high temperatures:
HO
The metabolism
of phosphoglycolate
involves
enzymes In
the peroxisome
and the
mitochondrion,
as well as the
chloroplast
The metabolism
of phosphoglycolate
involves
enzymes In
the peroxisome
and the
mitochondrion,
as well as the
chloroplast
The metabolism of phosphoglycolate involves enzymes In the chloroplast,
peroxisome and the mitochondrion, as well as the chloroplast
2 RuBP + 2 O2
2 P-glycolate +
2 PGA
O2
ATP
2P
PGA
CO2
2 RuBP + 3 O2 + ATP
3 PGA + CO2 + 2 Pi
3 PGA
Why does high temperature promote photorespiration?
CO2 vs O2 solubilities
An increase in temperature lowers the concentration of
CO2 in the cytoplasm relative to the concentration of O2.
Is the formation of P-glycolate by rubisco an “evolutionary
mistake,” which occurred because the primordial atmosphere
had a low O2 concentration?
If high temperatures increase photorespiration, will
global warming result in a decrease in plant productivity?
If high temperatures increase photorespiration, will
global warming result in a decrease in plant productivity?
Or will an increase in atmospheric CO2 produce a general
increase in plant productivity?
The high temperatures excluded gymnosperms, especially from low latitudes.
Some plants show better net photosynthesis at high temperatures
than others.
Some plants show better net photosynthesis at high temperatures
than others.
Apparent photosynthesis
=
Gross photosynthesis
- Photorespiration
- Mitochondrial
Respiration
What accounts for the
difference in optimum
temperature between
Spartina and Leucopoa?
Summary
•The apparent rate of photosynthesis is a function of temperature,
with most plants showing a maximum at about 25oC.
•Rubisco can react with O2, to produce P-glycolate and P-glycerate.
•The metabolism of phosphoglycolate results in O2 uptake and CO2
production: photorespiration.
•High temperature promotes photorespiration by increasing O2/CO2.
•Some plants show maximum photosynthesis at 35-45oC.