Hello,
We had the same question, a couple of years ago. The solution we found was
using Congo Red, it stains cellulose but also other linear polysacharides. 
The dye is water soluble and is excited as well with the
blue as the green line of any standard confocal laser or standard
fluorescence microscope. 
See details in: J-P Verbelen and D. Stickens: "In vivo determination of
fibril orientation in plant cell walls with polarization CLSM" Journal of
Microscopy 177, 1-6, 1995. 
Or send an e-mail directly to my address.

Good luck

Jean-Pierre Verbelen
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  J-P. Verbelen                              E-mail: [log in to unmask]
  University of Antwerp (UIA)                          Tel:+32-3-820-22-77
  Department of Biology                                Fax:+32-3-820-22-71
  Universiteitsplein 1       B-2610 Wilrijk 
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On Fri, 17 Apr 1998, Franco Pedreschi wrote:

> Hello:
> I am studying celular walls in potatoes during frying using laser
> scanning confocal
> microscopy in its fluorescence mode ( we have lasers of 488 and 514
> nm).  For this reason I need a fluorochrome specific for vegetable walls
> 
> whose excitation wavelength be in the range of the lasers we have.    Do
> 
> you know any fluorochrome for staining cellular capable of being excited
> 
> by any of the mentioned lasers?  I will appreciate any help or
> information you give me.  Thanks in advance for your attention .
> 
> 
> --
> 
> MSc Franco Pedreschi
> PhD Student
> Pontificia Universidad Católica de Chile
> Department of Chemical Engineering and Bioprocesses
> e-mail:[log in to unmask]
> Phone:(56-2)6864264
> Fax:(56-2)6865803
>