Cell-wall and vacuolar invertases (beta-D-fructofuranosidase, EC 184.108.40.206) from Arabidopsis thaliana (L.) Heynh. are encoded by at least four genes, namely At beta fruct1, At beta fruct2, At beta fruct3 and At beta fruct4. Different A. thaliana organs from four developmental stages and under different environmental conditions were analyzed for invertase gene expression. Our results clearly show that both the cell-wall and vacuolar invertase genes are expressed in a development and organ-specific manner. No transcripts of the cell-wall invertase gene At beta fruct1 were found in the cotyledons; however, relatively high levels were detected in the leaves of mature plants. The expression of the second cell-wall gene At beta fruct2 was found to be flower-specific, conversely no expression of At beta fruct1 was detected in flowers. The vacuolar gene At beta fruct3 shows a distinctly different regulation of expression from At beta fruct1. Northern and reverse transcriptase-polymerase chain reaction analyses revealed the presence of transcripts in the cotyledons and only low levels in leaves, roots and flower buds. The second vacuolar invertase gene, At beta fruct4, was found to be expressed in leaves of very young plants, but no transcripts were detected in the leaves of mature flowering plants. In order to investigate the respective roles of invertases and sucrose synthase, a comparative analysis of the expression of these genes was carried out. The present study shows that cell-wall and vacuolar invertase genes are differentially regulated by environmental factors.