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In order to determine whether hydrogen peroxide (H 2 O 2 ) generated by polyamine oxidative degradation is involved in the development of lateral roots in soybean, the length and the number of lateral roots, the activities of polyamine oxidases and diamine oxidases, and the endogenous free polyamine and H 2 O 2 content were analyzed in soybean (Glycine max (Linn.) Merr.) main roots of 2-d-old seedlings after treatments for 2 d with exogenous β β β β β-hydroxyethylhydrazine (an inhibitor of polyamine oxidases), H 2 O 2 , putrescine, cyclohexylamine (an inhibitor of spermidine synthase) or N,N'-dimethylthiourea (a scavenger of hydrogen peroxide). β β β β β-hydroxyethylhydrazine treatment strongly inhibited the development of lateral roots in soybean seedlings, reduced the activities of polyamine oxidases and diamine oxidases, decreased H 2 O 2 levels, and led to the accumulation of endogenous polyamines in the main roots. The inhibitory effect of β β β β β-hydroxyethylhydrazine on root development could be alleviated by exogenously applied 10 µmol/L H 2 O 2 (a major product of polyamine oxidation). Treatment with cyclohexylamine and putrescine promoted root growth slightly, but treatment with cyclohexylamine plus N,N'-dimethylthiourea or putrescine plus N,N'-dimethylthiourea prevented the development of soybean lateral roots. The effects of these treatments on the development of soybean lateral roots were consistent with the changes in endogenous H 2 O 2 levels. These results suggest that the development of soybean lateral roots is associated with the oxidative degradation of polyamines, and that their products, especially H 2 O 2 , are likely to play an important role in the growth of soybean lateral roots.

Proline accumulation was studied in the leaves of Glycine max (L.) Merr. subjected to salt stress in the presence of aminoguanidine (AG, a specific inhibitor of diamine oxidase, DAO) and exogenous putrescine (Put). Both DAO activity and proline content were increased while endogenous Put content was decreased in soybean leaves under 50 to 150 mM NaCl. There was a negative correlation between proline accumulation and endogenous Put content. The addition of AG during NaCl stress inhibited DAO activity, caused Put accumulation and a 15 to 20 % decrease in proline content. Application of 1 mM Put to NaCl solution markedly increased proline content. The promotive effect of Put application could be alleviated by the treatment with Put plus AG. Moreover an application of AG had no effect on proline accumulation in soybean seedlings grown under normal condition. These results indicate that the quantitative contribution of Put degradation to proline formation is 15 to 20 %.Additional key words: Glycine max, NaCl-induced stress, polyamine degradation.

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