The isolation of an elongation-specific endo-1,4-beta-glucanase-cel1 from Arabidopsis thaliana was made possible by the fact that considerable homology exists between different endo-1,4-beta-glucanase (EGase) genes from different plants. Degenerate primers were synthesized based on two conserved regions from the avocado and tomato cellulase amino acid sequences. The A.thaliana cel1 cDNA gene was found to encode a 54kDa protein; sequence comparison with the avocado EGase revealed 56% identity. Northern blot analysis of cel1 suggested its developmental regulation. RNA transcripts were undetectable in fully expanded leaves as well as at the basal internode of flowering stems. However, a strong transcript signal was detected in the elongating zone of flowering stems of normal plants. The RNA transcript level of cel1 in the elongating zone of dwarf flowering stems was significantly lower than in the corresponding zone in normal plants. This suggests cel1's involvement in cell elongation in A. thaliana. Transgenic tobacco plants transformed with the putative cel1 promoter region fused to the gus reporter gene, showed a significant GUS staining both in shoot and root elongating zones. These results further substantiate the link between cel1 expression and plant cell elongation.