Jacob Knecht wrote: > Dear PBS members, > > Though I am not a professional pathologist, I am a passionate horticulturist > and conservationist. Ben Zonneveld brings up a good point. Not all viruses > reduce a plant's vigour nor are viruses responsible for many variegations > (especially foliar) found in ornamental plants today. Some viruses are now > essential to modern biological research methods... 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