Expression of C-assimilating enzymes in pea (Pisum sativum L.) root nodules.: In situ localization in effective nodules

Full length cDNAs encoding alcohol dehydrogenase (ADH), fructose-1,6-biphosphate aldolase (ALD), nodule-enhanced malate dehydrogenase (neMDH), phospho-enolpyruvate carboxylase (PEPC), and nodule-enhanced sucrose synthase (neSS) were isolated from a pea (Pisum sativum L.) root nodule cDNA library and characterized. Transcript abundance and cellular expression patterns for each gene were examined at different stages of nodule development. All the genes were expressed prior to the induction of nitrogenase suggesting a developmental signal as the initial trigger for expression. RNA tissue blots demonstrated that all the genes except ALD exhibit enhanced expression in effective nodules. In situ hybridization studies showed contrasting patterns of gene expression within various nodule zones. The highest expression of ADH was observed in interzone. ALD was expressed predominantly in nodule meristem, invasion zone and interzone. The neSS transcripts were found rather uniformly throughout the nodule. Expression of neMDH and PEPC was also detected throughout the nodule, but the highest levels were associated with interzone and N-2-fixing zone.