Regulation of the cytosolic fructose-1,6-bisphosphatase by post-translational modification and protein level in drought-stressed leaves of sugarbeet
1992
Harn, C. | Daie, J.
Sugarbeet plants (Beta vulgaris, L.) were grown in a growth chamber and subjected to a slow-developing (in vivo) period of drought stress by withholding water. During an 8 day period, several parameters were monitored. A gradual and consistent decline was observed in the activity of the cytosolic fructose-1,6-bisphosphatase (FBPase) during the first 3-4 days of stress. During this initial period, leaf water potential had declined from -0.8 MPa, but no significant changes were observed in hexose, sucrose and starch contents, levels of FBPase protein and transcript and sucrose-phosphate synthase (SPS) transcript. Major changes in all parameters occurred during the latter stages of stress. At the end of this period, water potential was -4.3 MPa, sucrose levels increased three fold, starch content declined to less than 10% and FBPase activity was about 40% of controls. SPS activity slightly declined under substrate-saturating conditions but increased (100%) under substrate-limited conditions. SPS transcript slightly declined only in severely stressed leaves. Protein and transcript levels of FBPase also declined, but substantial amounts remained in these leaves suggesting that sugarbeet has a relatively resilient system for sucrose synthesis. During the initial stages, the decline in FBPase activity was coupled with stable protein level, suggesting post-translational modification of the protein. Later, regulation appeared to involve decline in the protein level. The data provide the first evidence for the coarse control of this enzyme in plants.
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