active transport

Dave Haas davehaas at
Tue Sep 28 18:31:36 EST 1999

Is it possible for plants to "actively transport" water?  Esau makes the 
statement that water may be actively transported in certain secretory 
structures. I had always thought that water was one thing that couldn't 
be actively transported.  Somewhere back in time I had acquired this 
idea.   Now.  I realize that there is not a molecular pump for water like 
there is for various ions,  but if you define active transport as simply 
using ATP to move something against a gradient shouldn't you be able to 
move water out of a cell like contractile vacuoles do in protists. 

This brings to mind another question.  Why would a plant want to rid 
itself of water in the first place?  If special cells (hydathodes) have 
evolved to release water in guttation there should be some advantage 
shouldn't there?  Are some plant cell walls unable to hold up under 
excess pressure produced by osmosis.  Anyone have any info in this area?

D. Haas

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