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Re: CO2 use at nightime?

     >Everybody knows that plants don't use CO2 at night right?
     
     >Not so fast! Thinking about Roger's calculations on CO2 use got me to
     >thinking. Plants don't use the CO2 directly, it has to go through
     >chemical precursor stages, right? That would imply that plants 
     >continue to absorb and store CO2 in various chemical forms in 
     >preparation for the days photosynthesis. What do you think?
     
     CO2 is used directly by plants; there is no chemical precursor or 
     storage product for CO2.  In the chloroplast, CO2 enters into the 
     Calvin Cycle and is added to a five-carbon compound, ribulose 
     1,5-bisphosphate. The resulting six-carbon compound is split, giving 
     two molecules of a three-carbon compound, 3-phosphoglycerate.  This 
     3-carbon compound is reduced and phosphorylated to form the 
     carbohydrate, triose phosphate.  Some of the triose phosphate 
     molecules are used to form sucrose and starch, while the rest is used 
     to regenerate ribulose 1,5-bisphosphate needed for the continuation of 
     the Calvin cycle. 
     
     The enzyme responsible for carboxylating ribulose 1,5-bisphosphate is 
     named, appropriately enough, ribulose bisphosphate carboxylase, or 
     rubisco, for short.  It is a water-soluble protein found in the 
     aqueous phase of the chloroplast outside of the photosynthetic 
     membranes.
     
     As each molecule of CO2 used requires 2 molecules of NADPH and 3 
     molecules of ATP, the Calvin Cycle can continue as long as there is 
     available NADPH and ATP (these compounds are re-generated from ADP and 
     NADP via photosynthesis).  
     
     Rubisco is found in photosynthetic and chemosynthetic organisms.  I 
     even found it in bacteria living endosymbiotically within the gill 
     tissues of a marine lucinid clam.  Check out:
     Fisher, M. and S. Hand.  1984.  Chemoautotrophic symbionts in the 
     bivalve Lucina floridana from seagrass beds.  Biological Bulletin 167: 
     445-459.
     
     Check out:
     http://www.life.uiuc.edu/govindjee/paper/gov.html
     especially section 5.7, for much more detail on photosynthesis.
     
     Regards,
     
     Mark