Mitogen-activated protein kinase and abscisic acid signal transduction

The phytohormone abscisic acid (ABA) is a classical plant hormone, responsible for regulation of abscission, diverse aspects of plant and seed development, stress responses and germination. It was found that ABA signal transduction in plants can involve the activity of type 2C-phosphatases (PP2C), calcium, potassium, pH and a transient activation of MAP kinase. The ABA signal transduction cascades have been shown to be tissue-specific, the transient activation of MAP kinase has until now only been found in barley aleurone cells. However, type 2C phosphatases are involved in the induction of most ABA responses, as shown by the PP2C-deficient abi-mutants. These phosphatases show high homology with phosphatases that regulate MAP kinase activity in yeast. In addition, the role of farnesyl transferase as a negative regulator of ABA responses also indicates towards involvement of MAP kinase in ABA signal transduction. Farnesyl transferase is known to regulate Ras proteins, Ras proteins in turn are known to regulate MAP kinase activation. Interestingly, Ras-like proteins were detected in barley aleurone cells. Further establishment of the involvement of MAP kinase in ABA signal transduction and its role therein, still awaits more study

Involvment of abscisic acid in drought and osmotic stress in rice cell suspension

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Abscisic Acid Induces Mitogen-Activated Protein Kinase Activation in Barley Aleurone Protoplasts.

Abscisic acid (ABA) induces a rapid and transient mitogen-activated protein (MAP) kinase activation in barley aleurone protoplasts. MAP kinase activity, measured as myelin basic protein phosphorylation by MAP kinase immunoprecipitates, increased after 1 min, peaked after 3 min, and decreased to basal levels after ~5 min of ABA treatment in vivo. Antibodies recognizing phosphorylated tyrosine residues precipitate with myelin basic protein kinase activity that has identical ABA activation characteristics and demonstrate that tyrosine phosphorylation of MAP kinase occurs during activation. The half-maximal concentration of ABA required for MAP kinase activation, 3 x 10-7 M, is very similar to that required for ABA-induced rab16 gene expression. The tyrosine phosphatase inhibitor phenylarsine oxide can completely block ABA-induced MAP kinase activation and rab16 gene expression. These results lead us to conclude that ABA activates MAP kinase via a tyrosine phosphatase and that these steps are a prerequisite for ABA induction of rab16 gene expression

Inactivation of a MAPK-like protein kinase and activation of a MBP kinase in germinating barley embryos

We provide evidence for involvement of two different 45 kDa protein kinases in rehydration and germination of barley embryos. In dry embryos, a myelin basic protein (MBP) phosphorylating kinase was detected, which could be immunoprecipitated with an anti-MAPK (mitogen-activated protein kinase) antibody. Rehydration of the embryo induced a decrease in activity of this 45 kDa MAPK-like protein kinase. In addition, activity of a MBP kinase of the same molecular weight was subsequently found to be induced. This second MBP kinase activity could not be immunoprecipitated with the anti-MAPK antibody and was induced only in germinating embryos, not in dormant embryos. (C) 2000 Federation of European Biochemical Societies. Chemicals/CAS: Abscisic Acid, 21293-29-8; Ca(2+)-Calmodulin Dependent Protein Kinase, EC 2.7.1.123; fusicoccin, 20108-30-9; Glycogen Synthase Kinase 3, EC 2.7.1.37; Glycosides; Mitogen-Activated Protein Kinases, EC 2.7.1.37; Plant Growth Regulators; Water, 7732-18-