Re infectivity of naked viral DNA

[ncel]

On 18 May, Patrick O'Neill wrote:

> I have heard of this method...and am wondering what else is involved. 
> What are the abrasive beads mixed with (solution)?  Perhaps some
> cellulase?  Also, this is still not in conflict with my original post
> about it:  in this procedure, cells walls are disrupted as are, perhaps
> (and to a much lessor extent) cell membranes.  The rubbing would then act
> to work polynuc into the interior of the cell, allowing transcription from
> those that are not sheared into fragments.  This is not the same as
> exposing completely intact plant cells to polynucs and waiting for action. 
> A normal cell is set up/evolved to avoid invasion by outside polynucs 
> because under most circumstances, foreign DNA/RNA means infection.  As it 
> goes, special manipulations or treatments must be used to get past 
> natural barriers to invasion, such as chemical solutions, etc, to disrupt 
> cell walls and membranes which THEN allows easy entry for polynucs.  
> 
> Try the same plant experiment: no abrasive, no rubbing.  Just add a drop 
> of TE plus viral DNA or RNA and watch for infection.  Another test would 
> be to add the same polynuc into liquid solution for growing seedlings and 
  > see if the resulting plants end up with infection of appropriate virus.  
> 
> 
> I do apologize if I come across too dogmatically, but I require strong 
> evidence to indicate that naked DNA or RNA and NO SPECIAL MANIPULATIONS 
> can produce anything but free nucleotides as a result of degredation.
> As it is, I will be picking up the references cited here to see if any of 
> them address the specifics of my objection or if they involve special 
> manipulations or solutions rather than simple "exposure."

If no "special manipulations" are allowed, then plants are susceptible
neither to free RNA/DNA nor to any viruses (intact nucleoproteins) as 
well! As has been known for a long time (1930's or so), inoculation of 
plants with viruses requires wounding. Experimentally, an abrasive 
(usually carborundum) is dusted onto the leaves prior to inoculation (or 
mixed with the inoculum). Optimal grid size has been empirically 
determined; presumably, if wounding is too severe, cells may die or 
release RNases, if too small, efficiency (number of virus particles 
entering cells) is too small. In nature, the cell wall barrier usually is 
overcome by insects equipped with ready-made hypodermic syringes or by slight
wounding brought about by, for example, brushing of leaves of infected 
plants against healthy ones (wind) or by tools used by farmers, etc.
    
Your proposed experiment (spraying of viruses or free RNA/DNA onto intact 
plants) has been made numerous times, always with negative results.

All this is just a bit of very basic plant virology; more details can be 
gleaned from any pertinent textbook, such as the excellent one by R.E.F. 
Matthews (Academic Press). Ted Diener