The Roles Of Polyamine Catabolism In Development And Salt Tolerance Of Soybean Seedlings

Polyamines (PAs), spermidine (Spd), spermine (Spm) and their diamine obligate precursor putrescine (Put), are small aliphatic amines that are ubiquitous in all plant cells. They have been proposed to be closely associated with development, morphogenesis and responses to diverse stresses. In comparison with large and detailed investigations focused on the regulation of free PA levels and biosynthetic enzyme activities, little attention was paid to the physiological roles of PA catabolism and its catabolic products. Particularly, there are only limited information on whether PA oxidation is involved in root development, and whether light promotes the synthesis of lignin through stimulating the activities of polyamine oxidase (PAO) and diamine oxidase (DAO). In addition, differences in PA catabolism of distinct salt tolerant genotypes in response to salt stress remain unknown. Whether PA oxidation under salt stress is implicated in a conversion to proline or accumulation of γ-aminobutyric acid is far from clear. Therefore, whether PAs accomplish their important functions in salt tolerance through modulating the accumulation of proline or GABA remains to be clarified. Here, two soybean [Glycine max (L.) Merr.] cultivars with different salt tolerance (Lee 68 cv., salt tolerant; SuXie-1 cv., salt sensitive) were used as experimental materials, using high performance liquid chromatography after different exogenous treatments according to different research purposes, to study the roles of PA oxidative degradation in development and salt tolerance of soybean seedlings. The results are as follow:2-Hydroxyethylhydrazine (2-HEH, a specific inhibitor of PAO and DAO) treatment strongly inhibited the development of lateral roots of soybean seedlings, decreased the activities of PAO and DAO as well as H₂O₂ levels, and led to the accumulation of endogenous free and conjugated PAs in main roots. This kind of 2-HEH inhibitory effect on soybean root development, however, could be alleviated by exogenously-applied 10 μ mol/L H₂O₂. The alleviative effects of exogenous H₂O₂ suggest H₂O₂ from PA oxidative...