The effects of diquat and ethephon (ethylene-releasing factor) on the formation of abscisic acid (ABA) were studied. Based on our data we have concluded that (+S)-ABA) and (-R)-ABA are the final products from the oxidative cleavage of carotenoids. From the chemical point these products are prooxidants. Biologically active form of ABA as an antioxidant is 1',4'-diol ABA. These experiments precisely define the role of 1',4'-diol ABA as being essential for the effective defense against oxidative agents. By contrast, exogenous application of (+S)-ABA) and (-R)-ABA as growth regulators demonstrated that these chemicals act as oxidative agents like as phenols.To prevent oxidative damages of the cellular biopolymers the cells increase the endogenous levels of antioxidants including 1',4'-diol ABA, prostaglandins (PGE and PGF). Hence, the increasing of endogenous concentration of (+S)-ABA) and (-R)-ABA influenced by diquat (as also by another stress) is the respond of living cells on the increasing of endogenous quantities of oxidative agents. In this connection we concluded that jasmonates are also the final products from oxidative cleavage of membraneous lipids.

Key words: abscisic acid, carotenoids