Plant-growth Substances Used as Herbicides

Many of the same conclusions may be drawn from results with synthetic auxins as from indole-3-acetic acid water intake increased, there was a lessening of the downward translocation of photosynthate with temporary increases of soluble carbohydrates in the leaves, and alterations appeared in the metabolic ratq and direction and in enzyme activity. However, the direct site of action is not known, and many of the effects are puzzling. n-Fructose oligosaccharides in artichoke and chicory storage-tissue were diminished by 70% (calculated on the content of dry matter) in 6 days 

Two essentially different views of the metabolism of (2,4-dichloro-phenoxy) acetic acid have been presented. The first12 -124 was based on a 3tudy with bean stems, which converted 42% of (2,4-dichlorophenoxy)-acetic acid-l4C into acidic, water-soluble substances. Two ether-soluble metabolites were formed, and the same two metabolites could be recovered, 

Other herbicidal phenoxyacetic and phenoxypropionic acids have some properties similar to those of (2,4-dichlorophenoxy)acetic acid, but often have quite different species selectivity. Some of the differences can be explained on the basis of molecular stability, persistence, or mobility in the toxic form, as well as on the basis of differences in solubility and in absorption through leaves or roots. 

Of the three jnonochlorophenoxyacetic acids, only the 4-chloro derivative is very active and is used to retard abscission of fruit. A study of the effects of the isomers on the carbohydrates of the bean plant showed that the alterations of the carbohydrates were not related to the growth-inhibiting mechanism.12 Reducing substances, starch, and sucrose decreased with all treatments, And the 2-chloro compound had the least effect polysacchar rides other than starch were not much altered. 

It is of interest that Aspergillus niger detoxified the (2-chlorophenoxy)-acetic and (4-chlorophenoxy) acetic acids by hydroxylation of the ring, with removal of the chlorine atom.180 

---