Spatial distribution and temporal accumulation of mRNA encoding diamine oxidase during lentil (Lens culinaris Medicus) seedling development

During the first phases of lentil epicotyl development (up to 72 h), diamine oxidase (DAO) mRNA accumulation and the time course of enzyme activity are correlated. In the following days total DAO activity remained unchanged but the mRNA level decreased. Both enzyme activity and mRNA accumulation showed a spatial distribution along the epicotyl that was also developmentally regulated. DAO mRNA accumulation along the 84-h-old epicotyls of both etiolated and light-grown seedlings parallels the distribution of enzyme activity, being higher in the basal zone of the epicotyl as compared to apical one. However, a detailed time course analysis on etiolated epicotyls showed that subsequently DAO mRNA level decreased progressively in the basal zone while remaining unchanged in the apical one, even if the enzyme activity in the basal zone was still higher as compared to the apical one. Moreover, a persistence of DAO activity was also observed in segments excised from etiolated epicotyls despite the decrease of mRNA level. These findings suggest that the increase of DAO activity during ontogenesis is likely to be due to transcriptional activation and not to modulation of specific activity, and that the protein turns over slowly. Finally, Southern analysis suggests that the lentil DAO gene may belong to a multigene family with a low number of copies and/or could also indicate the occurrence of some related genes.