Re: Why does photorespiration increase when temperature increase

The decrease in photosynthesis rate, or rise in photorespiration, as temperature
increases is due to an increase in the affinity of rubisco and oxygen. Rubisco
combines more with oxygen relative to carbon dioxide as temperature rises, which
slows the rate of photosynthesis. In other words, rubisco acts mainly as a
carboxylase (combining with carbon dioxide) at lower temperatures but acts more
as an oxygenase (combining with oxygen) at higher temperatures. 

There are at least three reasons for the above: 

1. High temperatures usually correlate with high light. The more light, the
greater the oxygen production in the light reactions of photosynthesis. 
2. Oxygen solubility in water declines less than carbon dioxide solubility as
temperature rises. 
3. Oxygenase activity of rubisco increases as temperature increases. The first
reference explains this  as follows: 

"This happens since the reaction of the 2,3-enediol intermediate (see above)
with O2 has a higher free energy of activation than the reaction with CO2.  Thus
oxygenation is more sensitive to temperature than carboxylation and increases
more rapidly as the temperature rises." 

A higher temperature makes it easier to reach the energy of activation. 

Recent research indicates that photorespiration is not the wasteful process
often assumed (Rachmilevitch et al. 2004). It appears to play an essential role
in plant nitrate metabolism.


References


Plant Biochemistry Lecture 2


Brown, H.B. and Morgan, J.A. 1980. Photosynthesis of Grass Species Differing in
Carbon Dioxide Fixation Pathways VI. DIFFERENTIAL EFFECTS OF TEMPERATURE AND
LIGHT INTENSITY ON PHOTORESPIRATION IN C3, C4, AND INTERMEDIATE SPECIES. Plant
Physiology 66(4): 541–544.


Jiao, J. and Grodzinski, B. 1996. The Effect of Leaf Temperature and
Photorespiratory Conditions on Export of Sugars during Steady-State
Photosynthesis in Salvia splendens. Plant Physiology 111: 169-178.

 
Rachmilevitch, S., Cousins, A.B. and Bloom, A.J. 2004. Nitrate assimilation in
plant shoots depends on photorespiration. Proc. Nat. Acad. Sci. 101(31):
11506-10.