shikimic acid accumulation after glyphosate treatment

[jcummins <jcummins@UWO.CA>]

In western US and Canada  grain and oilseed  crops are frequently
treated with glyphosate  just prior to harvest that treatment  provides
a desiccant effect leading to uniform finishing of the seed. If early
frost is predicted the herbicide  acts to mature the seed  to avoid
costly frost damage.  In wheat the herbicide treatment leads to
accumulation of shikimic acid as is shown  in the paper below.
Shiikimic acid is a concern because its  accumulation to high levels may
produce wheat  that promote  cancer  or to the production in the wheat
of tannins that are toxic to humans and animals. Cattle and horses that
eat bracken fern rich in shikimic acid  suffer high cancer incidence or
toxicity from tannins.
J. Agric. Food Chem., 51 (14), 4004 -4007, 2003. 10.1021/jf0301753
S0021-8561(03)00175-4
Glyphosate Applied Preharvest Induces Shikimic Acid Accumulation in Hard
Red Spring Wheat (Triticum aestivum)
Gail A. Bresnahan,* Frank A. Manthey, Kirk A. Howatt, and Monisha
Chakraborty
Department of Plant Sciences and Department of Cereal and Food Sciences,
North Dakota State University, Fargo, North Dakota 58105

Abstract:

Glyphosate is a nonselective herbicide used as a harvest aid in a
variety of crops. Glyphosate is absorbed into the foliage and
translocated to metabolically active regions in the plant where it
interferes with the shikimic acid pathway. Experiments were conducted to
determine the accumulation and distribution of shikimic acid in wheat
treated with glyphosate at soft and hard dough stages of kernel
development and to determine the fate of shikimic acid during milling
and bread making. Elevated levels of shikimic acid were detected
throughout the wheat plant. Shikimic acid concentrations peaked 3-7 days
after treatment and then declined until harvest. Shikimic acid content
was 3-fold greater in flour and 2-fold greater in the bread derived from
treated wheat than nontreated wheat. Similarly, elevated levels of
shikimic acid were found in the crumbs and crust of bread made with
flour from glyphosate treated wheat. Glyphosate applied preharvest
resulted in shikimic acid accumulation in hard red spring wheat and
subsequent end-use products.