Safener seed treatment

A fundamental problem for safener discovery and development is to find safeners that do not also antagonize weed control. The fruits of Gulf Oil Company research (reported by Hoffmann in 1969) was 1,8-naphthalic anhydride (NA), which works best as a seed treatment, whereby antagonism of weed control is not an issue. To the authors knowledge just over a dozen further safeners have been commercialized in the years since NA was introduced, although several of the early safeners have since been superseded and/or withdrawn. This subse-... 

NA had also a stimulatory effect on the oxidative metabolism of the herbicide bentazone. Microsomal preparations of etiolated shoots from maize, which had received a seed treatment with NA, showed activity of a bentazone hydroxylase, which was not detectable in extracts from controls without safener pre-treatment [35]. Also, the improved tolerance of maize to the imidazolinone AC263222 after NA seed treatment could be related to enhanced AC 263222 hydroxylation by stimulation of a cytochrome P450 monooxygenase [31]. 

In the 1970s compounds were developed which eliminated these harmful effects on the growth of crop plants. They can be applied for the treatment of the seeds or admixed with EPTC in a quantity of 5-10%. These antidotes or safener substances presumably exert their action by stimulating the functioning of the EPTC-detoxicating enzyme of crop plants, of glutathione-S-transferase. This theory is supported by the observation that sensitive and tolerant plants absorb and translocate EPTC to essentially the same extent, but in tolerant plants the active substance is rapidly metabolised oxidatively to sulfoxide, then to biologically inactive sulfon derivatives, while in sensitive plants this process is slower and the plant meanwhile dies. 

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