| Summary: | 碩士 === 國立成功大學 === 生物學系碩博士班 === 90 === Protein phosphorylation and dephosphorylation are involved in the regulation of many eukaryotic intracellular processes. Protein tyrosine phosphorylation catalyzed by protein tyrosine kinase is important in the control of fundamental cellular activities. In animal system, protein tyrosine phosphorylation and dephosphorylation play a central role in a variety of signal transduction pathway regulating cell growth, development and differentiation. Though there were increasing evidences to the importance of reversible protein phosphorylation in cell responses to external stimuli in plants, data related to the involvement of protein tyrosine phosphorylation in plant growth and development was limited.
Rooting initiation involves cell divisions of induced cells followed by the formation of a root meristem. In Arabidopsis, root organogenesis in vitro can be induced from hypocotyls by a two step culture method. Hypocotyls are pre-cultured on callus-inducing medium and then transferred onto root-inducing medium for root re-differentiation.
We have investigated the possible role of tyrosine phosphorylation in this process with hypocotyls explants of Arabidopsis thaliana. Phytohormone-stimulated cell cycle reactivation in hypocotyls was accompanied by tyrosine phosphorylation of several proteins. Such regulation of the tyrosine phosphorylation in these proteins was not observed in a callus-formation mutant, srd2, a result which suggested that the induction of tyrosine phosphorylation occurs as a specific event in the cell cycle re-entry. Additionally, treatment of hypocotyls with a protein kinase inhibitor, staurosporine, and tyrosine phosphatase inhibitors, sodium orthovanadate and PAO, prevented the induction of cell division by phytohormones.
To investigate molecular mechanisms controlling root development, we examined the possible role of protein tyrosine phosphorylation during root organogenesis. The disappearance of three tyrosine-phosphorylated proteins at 63, 70 and 80 kDa correlated with the induction of root organogenesis was detected. We also found that tyrosine phosphatase inhibitors, V and NH4-molybdate, were able to inhibit root re-differentiation. This study highlighted that the role of protein tyrosine phosphotase(s) may play an important regulatory role in root development.
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