SPATIAL-DISTRIBUTION AND TEMPORAL ACCUMULATION OF MESSENGER-RNA ENCODING DIAMINE OXIDASE DURING LENTIL (LENS-CULINARIS MEDICUS) SEEDLING DEVELOPMENT

During the first phases of lentil epicotyl development (up to 72 h), d iamine oxidase (DAO) mRNA accumulation and the time course of enzyme a ctivity are correlated. In the following days total DAO activity remai ned unchanged but the mRNA level decreased. Both enzyme activity and m RNA accumulation showed a spatial distribution along the epicotyl that was also developmentally regulated. DAO mRNA accumulation along the 8 4-h-old epicotyls of both etiolated and light-grown seedlings parallel s the distribution of enzyme activity, being higher in the basal zone of the epicotyl as compared to apical one. However, a detailed time co urse analysis on etiolated epicotyls showed that subsequently DAO mRNA level decreased progressively in the basal zone while remaining uncha nged in the apical one, even if the enzyme activity in the basal zone was still higher as compared to the apical one. Moreover, a persistenc e 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 d ue to transcriptional activation and not to modulation of specific act ivity, and that the protein turns over slowly. Finally, Southern analy sis 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.