C-4 trees

John Penny j.penny at bell.ac.uk
Thu Nov 21 06:55:50 EST 1996


rmewing at molbiol.ox.ac.uk wrote:

>J. Penny states that C4 plants tend to be monocotyledons...
>There are however, many dicot families which show C4 photosynthetic carbon 
>fixation.

I suspect there may be confusion here between C4 photosynthesis and
CAM given that these two forms of photosynthesis involve similar
biochemical pathways but different approaches to the 'problem' of
separation of the initial CO2 fixation step and refixation after
decarboxylation has occurred. In C4 plants the separation is spatial
and those plants with true C4 photosynthesis (as opposed to C3-C4
intermediates) have a specialised leaf anatomy (mesophyll cells, PEP
carboxylase and bundle sheath cells, RUBISCO). CAM plants don't have
Kranz anatomy, instead separation of the intial fixation of CO2 to
malate occurs at night and decarboxylation, and recarboxylation
forming PGA, occur during the day. 

A useful reference is: Hall, DO, Scurlock, JMO, Bolhar-Nordenkampf,
HR, Leegood, RC & Long, SP (1993) Photosynthesis and Production in a
Changing Environment. Chapman & Hall, London. ISBN: 0 412 42910 1.

Years ago, when I was a PhD student working on Laminaria saccharina,
there was a lot of discussion in the literature about the possibility
of brown macroalgae like Macrocystis, Laminaria and Fucus having dark
fixation (essentially similar to CAM). 

Does any know the current thinking on the nature of photosynthesis in
the algae ? Apart from teaching a 1st year class on Plant Biology, Ive
moved away from the subject into pollution ecology and environmental
management. One gets rusty incredibly quickly these days because there
is so much stuff to read 




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