Fwd: [Plant-education] Glucose is no more a product

Bob Wise via plant-ed%40net.bio.net (by wise from uwosh.edu)
Wed Dec 19 11:32:09 EST 2007


>Forgive me for returning to an old theme that I have troubled you with in
>the past.
>
>For half a century or more, it has been clear that the path of
>starch synthesis in chloroplasts starts with triose
>phosphates and progresses to polymer formation via
>glucose-1-P rather than free glucose. Glucose is no more a product of carbon
>assimilation by illuminated chloroplasts than is sucrose.
>So, why do textbooks insist that it is?.
>
>If you wish to read a recent article about this you can find it by pasting
>DOI 10.1007/s11120-007-9139-3
>into Google
>
>Best Christmas wishes
>>From David Alan Walker, FRS; Emeritus Professor of Photosynthesis,
>University of Sheffield, UK.

David,

This has frustrated me too, and I have always 
ascribed it to the fact that most biology 
textbooks are written by non-plant biologists who 
think that chloroplasts are merely green 
mitochondria that perform reverse respiration. 
With that mindset, and given that glycolysis 
clearly starts with glucose, then photosynthesis 
must produce glucose in order for the mythical 
symmetry to be maintained.

Yes, it's both false and foolish.

Another chloroplast/mitochondrion myth that 
drives me bonkers the the oft-repeated 
(mis-)statement that mitochondria and 
chloroplasts are both bounded by a double 
membrane.  That is only true if your sole source 
of data is electron microscopy and all you are 
looking at is STRUCTURE.  Two lines around the 
mito--two lines around the chloro--must be the 
same.  If however, you actually start asking 
questions about the FUNCTION of those membranes 
(and I certainly hope my students ask those sorts 
of questions) then you have misled the reader. 
Just ask yourself questions like, "where is 
chemiosmosis taking place--which membrane?  Lipid 
synthesis?  Carotenoid synthesis?  Metabolite 
transport?" and the analogous double membrane 
myth quickly falls apart.

To quote me (from "The Structure and Function of Plastids"  Springer)=


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