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Abstract susan


Abstract susan

نام فایل : Abstract susan

فرمت : .doc

تعداد صفحه/اسلاید : 21

حجم : 20 مگابایت


Abstract
The ubiquitin/proteasome pathway represents one of the most important proteolytic systems in eukaryotes and has been proposed as being involved in pollen tube growth, but the mechanism of this involvement is still unclear. Here, we report that proteasome inhibitors MG132 and epoxomicin significantly prevented
Picea wilsonii
pollen tube development and markedly altered tube morphology in a dose- and time-dependent manner, while hardly similar effects were detected when cysteine-protease inhibitor E-64 was used. Fluorogenic kinetic assays using fluorogenic substrate sLLVY-AMC confirmed MG132-induced inhibition of proteasome activity. The inhibitor-induced accumulation of ubiquitinated proteins (UbPs) was also observed using immunoblotting. Transmission electron microscopy revealed that MG132 induces endoplasmic reticulum (ER)-derived cytoplasmic vacuolization. Immunogold-labeling analysis demonstrated a significant accumulation of UbPs in degraded cytosol and dilated ER in MG132-treated pollen tubes. Fluorescence labeling with fluorescein isothiocyanate-phalloidin and
β
-tubulin antibody revealed that MG132 disrupts the organization of F-actin and microtubules and consequently affects cytoplasmic streaming in pollen tubes. However, tip-focused Ca
2+
gradient, albeit reduced, seemingly persists after MG132 treatment. Finally, fluorescence labeling with antipectin antibodies and calcofluor indicated that MG132 treatment induces a sharp decline in pectins and cellulose. This result was confirmed by Fourier transform infrared analysis, thus demonstrating for the first time the inhibitor-induced weakening of tube walls. Taken together, these findings suggest that MG132 treatment promotes the accumulation of UbPs in pollen tubes, which induces ER-derived cytoplasmic vacuolization and depolymerization of cytoskeleton and consequently strongly affects the deposition of cell wall components, providing a mechanistic framework for the functions of proteasome in the tip growth of pollen tubes.
References
Most cellular proteins are continuously synthesized and degraded within the lifespan of a cell. Efficient protein turnover is essential for many aspects of cell physiology and development (
Hellmann and Estelle, 2002
). As one of the most important proteolytic pathways in eukaryotic cells, the ubiquitin/proteasome pathway (UPP) is believed to be involved in the degradation of the bulk of intracellular proteins, including misfolded proteins and short- and long-lived regulatory proteins (
Glickman and Ciechanover, 2002
;
Ciechanover, 2005
;
Hershko, 2005
;
Varshavsky, 2005
). Therefore, the biological functions of the UPP in both animal and plant systems have received considerable attention.
...


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