POLYAMINE CATABOLISM IN DORMANT EMBRYOS OF THE SPINDLE TREE (EUONYMUS-EUROPAEUS L) AND IN DORMANCY BREAK OBTAINED AFTER TREATMENT WITH GIBBERELLIC-ACID

Previously we showed that dormancy break of spindle tree embryos after gibberellic acid (GA(3)) treatment was followed by an increase in arg inine decarboxylase (ADC) activity (Beranger-Novat N. et al., Plant Sc . 102: 139-145, 1994). These results indicated that arginine decarboxy lase pathway mediate hormone-induced growth responses in spindle tree embryos. In the present investigation we show that in GA(3)-treated em bryos diamine oxidase (DAO) increases immediately after putrescine con tent and the increase in DAO activity paralleles the accumulation of p utrescine at the beginning of the culture (before the visible appearan ce of the radicle). In this system polyamine oxidase (PAO) increases i mmediately after DAO activity and follows closely the increase in sper midine content. These results demonstrate a direct correlation between the biosynthesis and oxidation of putrescine and spermidine. At every stage of development DAO and putrescine levels are lower than spermid ine and PAO levels. Dormant embryos can be distinguished from GA(3)-tr eated embryos by a complete lack of putrescine accumulation. In dorman t embryos compared to GA(3)-treated embryos DAO changed more or less i n parallel and on the whole seemed to follow the same content and dist ribution, but the kinetics of the activation of DAOs were different in dormant embryos with a delay of 1.5 day for the first and 1 day for t he second peak. During the first days of culture at least up to 4 days the distribution of spermidine and PAO in GA(3)-treated embryos follo wed the same pattern observed in dormant embryos, but the levels of sp ermidine and PAO were greatly reduced in dormant embryos. On the other hand the kinetics of the activation of PAOs were different in dormant embryos with a delay of 1 day. The results suggest that dormant embry os are deficient in their ability to synthesize polyamines efficiently and support the view that spermidine catabolism (via PAO pool) is lim iting in untreated embryos during the first days of culture.