J Integr Plant Biol. ›› 1998, Vol. 40 ›› Issue (2): -.

• Research Articles •    

Effect of Osmotic Shock on Protein Phosphorylation in Dunaliella salina Cells

CHEN Si-Xue, LI Lin and JIAO Xin-Zhi   

Abstract: Protein phosphorylation and dephosphorylation are considered as important regulatory mechanisms by which the activity of key enzymes and receptor molecules is altered within cells in response to a wide variety of external stimuli. Previous work is mainly on the purification and characteristics of protein kinase, but the role in stimulus-coupled responses in plants is not very clear. Experiments of in vitro protein phosphorylation demonstrated that in the extract of soluble protein of Dunaliella salina (Dunal) Teed. the activity of some protein kinases was, to some extent, dependent on the calcium concentration. The effects of calcium, verapamil, EGTA and A23187 on the in vivo protein phosphorylation also showed that calcium was important. In comparison, the autoradiograph of the in vivo phosphorylation was different from that of the in vitro phosphorylation. Addition of calcium or molybdate, an inhibitor of phosphatase, increased the extent of protein phesphorylation to a much higher level in hypoosmotic shocked samples (OSS), whereas as in hyperosmotic shocked samples(ESS) ,the extent of protein phosphorylation was lower than the control. In the absence of calcium or molybdate, the stimulation of protein phosphorylation by osmotic shock was hardly observed. The reason for this could be that the osmotic shock inhibited calcium uptake and/or activated protein phosphatase. The response of the intensely labelled 24 kD protein to osmotic shock was further studied. In the absence of calcium, the protein in OSS was more highly phesphorylated than the control and ESS. An increase of the eytosol calcium concentration stimulated phosphorylation of this protein in OSS, but had little effect on ESS. Such differences of calcium effects on protein phosphorylation indicated that the respective mechanisms of signal transduction mediated by protein phosphorylation may not be alike.

Key words: Protein phosphorylation, Dunaliella saliva, Osmotic shock

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