CAM help

[Joseph.Holtum]

Doug,

 CAM on land:
The stomata, open during the dark, close soon after the onset of the light 
period. Malic acid diffuses from the vacuoles to be decarboxylated (i) in 
the cytoplasm by either NADP malic enzyme or PEP carboxykinase, or (ii) in 
the mitochondria via NAD malic enzyme.
The internal CO2 concentration increases (remember the stomata are closed) 
to levels at which the oxygenase activity of rubisco is supressed. So no 
photorespiration.
Photorespiration can occur during the afternoon if the stomata open and C3 
metabolism occurs.
So yes, the CAM syndrome reduces water loss because stomata are open during 
the coolest, most humid time of the day, but CAM is also associated with 
reduced photorespiration.
(look for CAM reviews (there is a new book on CAM edited by Klaus Winter and 
Andrew Smith) or the original article by Bill Cockburn ...I've forgotten the 
year, late 70s or early 80s I think)


 CAM in aquatic plants is obviously not an adaptation for water stress!!
Aquatic CAM species generally inhabit either (i) oligotrophic waters 
containing little dissolved inorganic carbon or (ii) fresh waters in which 
there are large blooms of vegetation that reduce the dissolved CO2 
concentration during the day. CO2 levels increase during the dark

In the oligotrophic lakes CAM is useful because PEP carboxylase can scavenge 
CO2 despite the high O2:CO2 i.e. CAM is used as a CO2 pump. 

In the lakes where there are vegetation blooms the CAM plants, being smart 
little buggers, fix their CO2 during the dark when CO2 levels are higher and 
there is little competition for CO2
(look for articles by Jon Keeley)

Isoetes adicola (I think)
A species that inhabits peat bogs on lake sides in the Andes of Peru. It has 
CO2 and H2O impermeable cuticl on its leaves and has no stomata!
CO2 diffuses up the stem from the boggy medium below! Perhaps CAM helps 
because the leaf is producing O2 and consuming CO2 therefore the CO2 has to 
diffuse up via a concentration gradient. If the CO2 is prodiuced directly in 
the leaf the CO2:O2 ratio shouldnt be a problem
(look for an article by Jon Keeley ... the species was called Stylites 
andicola at that time)

Cheers and beers

Joe Holtum
 CAM rules!.....but what ARE the rules?

Joe Holtum
Department of Tropical Plant Sciences,
James Cook University of North Queensland,
Townsville, North Queensland 4811

Telephone:-          (077) 81 4391 (lab); 79 5252 (home)
Facsimile:-             (077) 25 1570
electronic mail:-    joseph.holtum at jcu.edu.au