photorespiration - why?

Bill Williams WEWilliams at OSPREY.SMCM.EDU
Thu Jan 8 12:06:53 EST 1998

I guess I've always felt it was an important scavenging mechanism, given the inevitability of the "O" activity in "RUBISCO."  I haven't looked at the very recent literature, but my recollection is that everybody who's found mutants in the pathway has found decreases in net carbon fixation, never increases, at least in normal concentrations of CO2 and O2, and I understand there are good fundamental chemical reasons why RUBISCO must be competitively inhibited by O2.  (The mutation work is significant here, too:  lots of mutations that decrease the CO2/O2 discrimination, none that increase it.) It does seem like an awfully complicated way to recycle that one C that might otherwise be lost from the Calvin cycle, but evolution is seldom neat and tidy.

Bill Williams
St. Mary's College of Maryland

>>> bill <WSCOHEN at> - 1/8/98 10:54 AM >>>
Biolabbers -

Boy, I'm full of questions today.  Probably because I'm so glad that
you're all back.

Each year when I teach photorespiration, I tear my hair out trying to
find out if anyone has a great hypothesis about any possible adaptive
value of this pathway.  Yeah, yeah, I know that it generates carbon
dioxide, and results in rubisco again fixing it and the Calvin cycle
resuming.  But at what cost?!?  Doesn't the organism get anything else
out of it?  Are some of the amino acids formed in the process used in
protein synthesis, or something like that?  I've searched the Net,
searched my plant physiology books, and can find nothing that I'm happy

Any ideas out there?


  Barb Beitch


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