Protein tyrosine phosphatase is possibly involved in cellular signal transduction and the regulation of ABA accumulation in response to water deficit inMaize L. coleoptile

Abstract

Water deficit-induced ABA accumulation is an ideal model or “stimulus-response” system to investigate cellular stress signaling in plant cells, using such a model the cellular stress signaling triggered by water deficit was investigated inMaize L. coleoptile. Water deficit-induced ABA accumulation was sensitively blocked by NaVO3, a potent inhibitor both to plasma membrane H+-ATPase (PM-H+-ATPase) and protein tyrosine phosphatase (PTPase). However, while PM-H+-ATPase activity was unaffected under water deficit and PM-H+-ATPase activator did not induce an ABA accumulation instead of water deficit, water deficit induced an increase in the protein phosphatase activity, and furthermore, ABA accumulation was inhibited by PAO, a specific inhibitor of PTPase. These results indicate that protein phosphtases may be involved in the cellular signaling in response to water deficit. Further studies identified at least four species of protein phosphtase as assayed by using pNPP as substrate, among which one component was especially sensitive to NaVO3. The NaVO3-sensitive enzyme was purified and finally showed a protein band about 66 kD on SDS/PAGE. The purified enzyme showed a great activity to some specific PTPase substrates at pH 6.0. In addition to NaVO3, the enzyme was also sensitive to some other PTPase inhibitors such as Zn2+ and MO3 3+, but not to Ca2+ and Mg2+, indicating that it might be a protein tyrosine phosphatase. Interestingly, the purified enzyme could be deactivated by some reducing agent DTT, which was previously proved to be an inhibitor of water deficit-induced ABA accumulation. This result further proved that PTPase might be involved in the cellular signaling of ABA accumulation in response to water deficit.