Self-inhibitors biological activity

Fig. 1 21]. An ABA concentration as low as 10 M is sufficient to enhance its own metabolism, and this effect can be observed within 2 h of ABA treatment [21]. The formation of the next stable metabolite, DPA, is not enhanced by pretreatments with either ABA or PA [21]. Thus, the enhanced PA formation is unlikely a scavenging mechanism to remove excessive ABA because the tissue would have to enhance the formation of DPA in order to eliminate the biological activities. The self-induction of ABA metabolism can be prevented by transcription and translation inhibitors, suggesting that ABA induces the monooxygenase (or a cofactor for this enzyme) responsible for PA formation. The regulation of ABA metabolism in barley aleurone layers is similar to the induction of nitrate reductase by its substrate, nitrate. In this latter case, treatment of a plant tissue with nitrate enhances its ability to metabolize nitrate. 

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