Thiocarbamates and Their Safeners

Thiocarbamate herbicides, which are normally applied preemergence, exert their herbicidal action at early stages of seedling growth. Grass and some broadleaf weeds are selectively controlled in com, cotton, soybean, and other crops, shoots being more sensitive than roots. In addition, a primary effect of these herbicides appears to be due to inhibition of cell elongation rather than cell division.  

Various actions of thiocarbamates on lipid contents, lipid labeling, membrane constituents, and growth regulators have been reported (see Ref. 59). In addition, several antidotes or safeners which increase the tolerance of crop plants to thiocarbamates have been shown to reverse the effects of these herbicides on lipid metabolism.  

In order to examine the apparently selective inhibition of very long chain fatty acid synthesis in vivo, experiments have been carried out in our laboratories using microsomal fractions these contain endoplasmic reticulum, which is the site of fatty acid elongation (Section 3.2). 

Using [ C]malonyl-CoA as precursor, microsomal fractions from pea seeds, germinated for 24 h, are able to label arachidic and, sometimes, behenic acids. At a concentration of 10 M, both diallate and triallate inhibited labeling of these fatty acids it was only at 10 M that a different pattern of labeled fatty acids was seen (Table 3.10). Thus, the rather selective 

Concentration of diallate (M) Total fatty acid labeling (% of control) Fatty acid labeling (% of total)  

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