Figure 1.

Activation of mitogen‐activated protein kinase (MPK)3/MPK6 induces the expression of glutamate decarboxylase (GAD)1 and GAD4 genes and leads to high level of gamma‐aminobutyric acid (GABA) accumulation

(A–C) Fourteen‐d‐old seedlings grown in gas chromatography vials supplied with swimming medium were collected at the indicated times after addition of 5 μmol/L dexamethasone (DEX). After reverse transcription, levels of GAD1 (A), GAD2 (B), and GAD4 (C) transcripts were determined by real‐time quantitative polymerase chain reaction (PCR). Relative expression was analyzed by two‐way analysis of variance (ANOVA) (genotype × time point). Different lowercase letters above the groups indicate statistically different groups (P < 0.0001). Error bars indicate SD (n = 3). (D) Fourteen‐d‐old, soil‐grown seedlings were sprayed with 30 μmol/L DEX. Leaves were collected at the indicated times after application of DEX. Gamma‐aminobutyric acid accumulation was determined using a Hitachi Automatic Amino Acid Analyzer, L‐8900. Gamma‐aminobutyric acid concentration was analyzed by two‐way ANOVA (genotype × time point). Different lowercase letters above the groups indicate statistically different groups (P < 0.001). The numbers above each bar at time zero indicate the low initial GABA level (μg/g FW). Error bars indicate SD (n = 3), FW, fresh weight.