Why we should care about pathogenic viruses in our plants
Lee Poulsen (Fri, 23 Jul 2010 06:36:34 PDT)

Jacob Knecht wrote:

I enjoyed Jacob's essay and it caused me to think of a couple of points:

1. Not only are some microorganisms not bad, the "flora" in human
gastrointestinal system for example, which we've known about for years,
is considered to be essential. So much so, that scientists decided to
sequence all of them and finally have done so, at least with a few
sample humans, to try to put together the "other" human DNA sequence (or
conglomeration of DNA) to find out what it is doing for us and how it
differs from one part of the world to another or from one culture to
another. I can't remember the figure, but something like 2 or 4 pounds
(1 or 2 kilos) of the average adult's total weight isn't even really
genetically ourself, but is all these other microorganisms. (I even have
one friend, who in his treatment for a very rare form of cancer, had to
have the entire flora killed. After they finished one stage of the
treatment, they had to reintroduce as much of the flora as they could,
and then wait for several weeks while he ate "normal" food so that the
flora could grow and fill all of the former niches in his gut as well as
allow for additional necessary flora from the food he ate to also enter
his system and grow into the areas needed, before they could continue
with the subsequent steps of his treatment.)

2. It is possible to eliminate virus from an infected plant. The
University of California Citrus agency or division, in conjunction with
the USDA I think, has a facility set up to do just this. (They also have
an elaborate and extensive set-up for quarantining new citrus
introductions from outside Calif. and maintaining virus-free budwood
trees of most of the citrus varieties grown in the U.S.) Apparently, in
a heated environment (greater than something like 105°F/40°C) the
growing tips at the extremities of a plant can grow faster than the
virus can travel to get to it. So they grow a plant in a special heated
room and after it's grow for a while, they carefully slice off just the
very newest cells at a growing tip. They then tissue culture these and
grow the plant until buds form, which they then graft onto virus-free
rootstock and eventually produce a virus-free version of the virused
citrus variety. Pretty amazing.

3. Which leads me to a third comment/question: I am not a biologist,
just someone very scientifically oriented and interested in many aspects
of science. However, even though I've read and heard a lot about how the
human body (and animals in general) fights viruses, antibodies, etc., I
have utterly no knowledge about how or whether plants fight viruses. Do
they produce antibodies? Do they have some other mechanism to do so? It
would seem that they have to do something or else by now the entire
plant kingdom would be either completely infiltrated with evolved
viruses, or extinct. If there is such a mechanism, wouldn't it be
possible to develop the equivalent or analog of vaccines for plants?
They've made vaccines for pet animals and agricultural animals; have
they tried creating the equivalent of vaccines for important commercial
crops, and it not, is it because such a thing is not possible? (I
realize that geophytes are far down the list in importance for making
"vaccines" against viruses. But I'm curious about why I've never heard
of medical methods to prevent virus infection in plants.)

--Lee Poulsen
Pasadena, California, USA - USDA Zone 10a