From ACLARK@crop.uoguelph.ca Sun Nov 16 11:47:50 1997 Date: Sun, 16 Nov 1997 06:25:35 EDT From: "E. Ann Clark, Associate Professor" To: sanet-mg@amani.ces.ncsu.edu Subject: Re: natural vs. synthetic biocides Steve and Rich have raised an interesting point for discussion, and one that I'd like to hear more about. It is quite entirely true that plants and perhaps other organisms (I am a plant scientist; like the hammer, everything looks like tacks!) have evolved an elegant arsenal of methods of avoiding herbivory - getting eaten. Some of these involve digestion, like tannins and lignins. Others act as vasoconstrictors - like alkaloids - which not only reduce palatability but cause a whole range of upsets in stock unfortunate enough as to be obliged to eat them (e.g. old style reed canarygrass cultivars and endophyte-infested tall fescue). There are whole textbooks on the neat evolutionary counterplay between hervivore and plant in the game of life. More recently, Theo Colborn in her new book Our Stolon Future talks about endocrine disrupters (ED)which are chemicals that mimic such compounds as estrogen or androgen or other key human regulators, causing all manner of havoc in developing embryos. Much of the book is about synthetic ED's, like DDT and PCB's. However, she goes into some depth about naturally occurring plant estrogens, and discussing a theory that plants may have evolved the ability to generate estrogen mimics as a vehicle to deter reproduction in herbivores. The timing of highest estrogen concentration in plant tissues, and the type of plant that expresses this trait (the tasty ones, not the ones already unpalatable to stock) support the notion that this is the intent. So, here is a case where "natural" estrogens might cause an effect analogous to "synthetic" estrogens - Steve's point. Examples include red clover and alfalfa. But she goes on to note that there are differences in the herbivore in how it responds to these outside influences. Herbivores (including humans) have apparently evolved a system of molecules which destroy the plant-origin estrogen-mimics, and maintain the correct, exceptionally low concentration of estrogen for fetal development (not wholly effective, as producers are still cautioned against grazing some species during flushing/breeding). So, herbivores have evolved in response to this selection pressure, just as one might suspect. Such is NOT the case for the synthetic estrogen-mimics, which are able to perist in excessive concentrations in the blood stream and do damage. So, while both natural and synthetic estrogen- mimics are present, herbivores are able to manage one but not the other - Rich's point. It is very important to distinguish between natural and synthetic products, whether estrogen-effectors or biocides. They are both intended to "kill" but natural origin stuff is part of an elegant evolutionary dance between equal partners. The synthetic stuff is a rude interloper against which natural systems have no defence. I'd be very interested to hear of other work along these lines. Ann ACLARK@crop.uoguelph.ca Dr. E. Ann Clark Associate Professor Crop Science University of Guelph Guelph, ON N1G 2W1 Phone: 519-824-4120 Ext. 2508 FAX: 519 763-8933 To Unsubscribe: Email majordomo@ces.ncsu.edu with "unsubscribe sanet-mg". To Subscribe to Digest: Email majordomo@ces.ncsu.edu with the command "subscribe sanet-mg-digest".