9211 Outline the role of phloem


 

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9.2.11 Outline the role of phloem in active translocation of sugars (sucrose) and amino acids from source (photosynthetic tissue and storage organs) to sink (fruits, seeds, roots).

The movement of organic molecules in plants is called translocation. The organic molecule are dissolved in water and the solution is referred to as phloem sap. 

So how does phloem move the phloem sap from the source to the sink?

   The movement of phloem sap is explained through the pressure-flow hypothesis

The sieve plate function is not clear.  Sometimes the pores are filled (viz callose) and there seems to be an associated protein that can be made to tightly fit in the poor - or change its shape and release the poor.  The mechanism is partly understood, but the purpose is currently unknown (see University of Hamburg's Botany hypertext.)

 

http://www.uic.edu/classes/bios/bios100/lectf03am/sucrosepump.jpg

 

 

Structure of Phloem (diagram)

<http://www.clt.astate.edu/mhuss/toppage6.htm>

 

 

Micrograph of phloem and seive plate ends

<http://www.uic.edu/classes/bios/bios100/lectf03am/phloem.jpg>

 

Phloem longitudinal section diagram

image from <http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.html>

 

Sieve plate

Image from <http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.html>

 

 

Micrograph of xylem and phloem showing relative positions.  (Note that position is reversed (left or right) relative to diagram below!)

image from <http://plantphys.info/plant_physiology/basiccytology1.shtml>

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

http://www.uic.edu/classes/bios/bios100/lectf03am/translocation.jpg&imgrefurl=http://www.uic.edu/classes/bios/bios100/lectf03am/lect20.htm

 

 <http://www.uic.edu/classes/bios/bios100/lectf03am/phloemwater02.gif>