A mechanism of coarse control of cytosolic FBPase under water stress has been investigated. Sugar beet plants grown in a green house were subjected to two different levels of water stress by withholding water: mild stress for 4 days and severe stress for 8 days. At mild stress, levels of transcript and protein in the leaves holding the water potential of -1.8 MPa were stable while the activity declined to 74% of control. At severe stress, the water potential in the leaves was approximately -4.0 MPa. The levels of the transcript and protein were 17% and 15% of the levels fo control, respectively, suggesting the cytosolic FBPase gene was not expressed continuously in severe stress. However, the activity was still present although it is low (33% ofcontrol). Two dimensional protein gel was performed to find changes in the amino acid residues by charge modification under water stress. The isoelectric pH for the cytosolic FBPase on the Western blot was 5.4 at 37 kDa. The identicla spot was found in different water stress levels indicating that protein modification of the cytosolic FBPase does not occur. Collectively, the regulation of cytosolic FBPase activity under water stress does not depend on the protein modification but depends on the biochemical levels at mild and the protein levels at severe stress.