A partial sucrose synthase clone was isolated from a nodule cDNA library of Lotus japonicus, which had strong homology to sucrose synthase genes from Vicia faba and other plant species. The transcript was 2.7 kb in size and expression was enhanced in nodules compared to roots of L. japonicus. Two overlapping genomic clones containing sucrose synthase sequences were isolated from L. japonicus with a view to mapping and analysing the promoter of this gene. The early nodulin ENOD2 is a (hydroxy)proline-rich cell wall protein, which is expressed in the inner cortex surrounding the infected region of root nodules. In order to see if this nodulin is involved in the operation of the oxygen diffusion barrier, L. corniculatus was transformed with antisense ENOD2 gene constructs derived from the promoter and coding sequence of soybean. Two of the 20 antisense plant lines had significantly lower dry weight and nitrogenase activity as well as a different O2 profile through the nodules when compared to control plant lines, but there was no difference in ENOD2 transcriptional activity between the control and antisense plants. Possible reasons for this observation are discussed.Peer reviewe