Re: [IAWA Forum] RE: Radial water transport

From: Rod Savidge <savidge@unb.ca>
Subject: Re: [IAWA Forum] RE: Radial water transport
Date: Mon, 07 Oct 2002 17:40:11 -0300

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One volume of ethylene dissolves in 9 volumes of water at 25 C, in 4 
volumes at 0 C.

Jorg Sauter suggested average long-term radial flux rates of sugars from 
phloem into xylem within the range of 100 to 200 pmol glucose per sq. cm 
(tangential lumen area of ray cells) per second, based on starch deposition 
rates in xylem ray cells (poplar, willow).  (Sauter, J 2000.  Photosynthate 
allocation to the vascular cambium: facts and problems, in Cell and 
Molecular Biology of Wood Formation, BIOS Sci., Oxford.)   The glucose (and 
other sugars) is dissolved in water, so the least complex hypothesis is 
that water flux through rays is the sugar transport mechanism.  Some 
apoplastic movement is also conceivable, but it would seem to be grossly 
inefficient to load glucose into the apoplast of phloem, move it through 
the apoplast into xylem, and then unload it to the cytoplasm of ray 
cells.    Energy has to be expended both to load and to unload.

Undoubtedly there are differences in radial transport between night (when 
starch in leaves is hydrolyzed and the phloem becomes charged with sugar) 
and day (when starch is retained in leaves).  Osmotic potentials and 
gradients from phloem to xylem must be oscillating diurnally.  I suspect 
that John Barnett's daytime observations on oak might yield a different 
outcome if repeated in the dark of night.

Rod

At 03:32 PM 07/10/2002 +0200, you wrote:
>But what about the functionality of intercellular spaces in gas exchange? 
>Is there not good evidence that morphogenetic triggers like ethylene move 
>in gaseous state through the intercellular spaces of sapwood xylem rays? I 
>forget the reference, but I think the IAWA J once published a paper on 
>this (by Aloni or Yamamoto?).
>Pieter Baas
>
>
>   At 08:44 PM 10/7/02 +0900, Peter Kitin wrote:
>>Hello forum members,
>>
>>Some adds to the comments of Dr. Donaldson,
>>There are abundand intercellular spaces in living rays, not only in dried 
>>wood, in the case of the hardwood Kalopanax pictus. It should be similar 
>>in conifer wood as well. If water in a living tree is transported through 
>>rays (don't know if there is evidence showing this),  I think the 
>>intercellular spaces should be more efficient for the movement of water 
>>than diffusion through cell walls, even if unlignified.
>>
>>Here is an image showing intercellular spaces in rays 
>><http://www.fagus.net/raycast1.jpg>http://www.fagus.net/raycast1.jpg . 
>>This is a resin cast of a fixed fresh sample of mature wood of Kalopanax 
>>pictus.
>>
>>With kind regards
>>
>>Peter Kitin, Ph.D.
>>JSPS Fellow
>>Laboratory of Wood Anatomy and Quality
>>Forestry and Forest Products Research Institute
>>P.O. Box 16, Tsukuba Norin Kenkyu Danchi-nai
>>Tsukuba Science City, Ibaraki
>>305-8687, Japan
>>Tel. (work): +81-(0)298-73-3211 ex.574 Fax.+81-(0)298-74-3720
>
>P. Baas
>Director
>Nationaal Herbarium Nederland
>Universiteit Leiden branch
>P.O. Box  9514,  2300 RA Leiden
>The Netherlands
>Phone: + 31 71 527 3515
>Fax:  + 31 71 527 3522
>new e-mail address: baas@nhn.leidenuniv.nl
>http://www.nationaalherbarium.nl/
>
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