Chemistry Reference
In-Depth Information
3.7 HERBICIDES
Herbicides are chemicals that inhibit or interrupt normal plant growth and devel-
opment. There are numerous classes of herbicides, having different modes of
action as well as different potentials for adverse effects on health and the envi-
ronment.
3.7.1 Herbicidal Peptides
Bialaphos (
68
) is a tripeptidic herbicide named N(4-[hydroxy(methyl)phos-
phinoyl]-L-homoalanyl-L-alanyl-L-alanine) that is produced by
Streptomyces
hygroscopicus
. Bialaphos is a protoxin which, upon metabolism in plants, is
converted to the active form called L-phosphinothricin (
69
). Phosphinothricin is
a structural analog of glutamic acid and acts a potent competitive and irreversible
inhibitor of the enzyme glutamine synthetase. Phosphinothricin has bactericidal
(against gram-positive and gram-negative bacteria), fungicidal (against
B.
cinerea
), and herbicidal properties (35). The inhibition of glutamine synthetase
causes the accumulation of ammonia and the inhibition of photorespiration,
resulting in glyoxylate accumulation in chloroplasts. In turn, this inhibition
causes the inhibition of ribulose bisphosphate carboxylase. Phosphinothricin is
also produced by the bacteria
S. hygroscopicus
and
S. viridochromogenes
.
Maculosin (
70
) is a cyclic dipeptide produced by
Alternaria alternata
and
is host-specific to spotted knapweed (
Cantaurea maculosa
). Maculosin-binding
activity has been detected toward receptors from spotted knapweed leaves.
Tentoxin (
71
) is a cyclic tetrapeptide by-product of
Alternaria alternate
.It
causes phytotoxic damage to both monocotyledonous and dicotyledonous weed
species. This secondary metabolite functions by inhibiting CF1 ATPase activity.
68
69
70
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