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KMID : 0368419970400030220
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Journal of Plant Biology
1997 Volume.40 No. 3 p.220 ~ p.226
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Modification of Cytosolic Fructose-1, 6-Bisphosphatase in Sugar Beet Leaves During Long-Term Dark Period
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Harn Chee-Hark
Daie Jaleh
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Abstract
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Sugar beet plants (Beta vulgaris L.) were exposed to long-term incubation in light (34 h) and dark (78 h) and changes in enzyme activity, protein and transcripts levels of cytosolic fructose-1,6-bisphosphatase (FBPase) in leaves were measured. The enzyme activity in leaves exposed to 34 h light was three times higher than the activity in leaves subjected to 78 h dark condition. Surprisingly, the enzyme activity was still remained stable even in the long-term dark treatment although the activity is lower. The transcript levels of cytosolic FBPase in 78 h dark were expressed equivalent to 10% of the expression occurred in 34 h light. However the protein levels remained unchanged in long-term incubation with either light or dark. The cytosolic FBPase protein was found to be modified during the long-tem dark incubation. The isoelectric pH for the protein spot detected by western blot on the two dimensional PAGE is 5. 4 in light sample while the pH value in dark sample is 6.0. Interestingly, the cytosolic FBPase in long-term dark treated leaves was activated 44% more by incubating in 50 mM mannose (sequestering agent of endogenous Pi) comparing to the activity with mannitol treatment as a control. Collectively, these data suggest that the cytosolic FBPase become less active by post-translational modification during a long-term dark period and this modification probably occurs due to the phosphorylation of the enzyme.
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