Histochemical straining and measurement of GUS activity in transgenic Arabidopsis thaliana . (a) a: 3-day-old seedling; b: 7-day-old seedling; c: mature leaf; d: root; e: microscopically observed root; f, g, i: transgenic plants treated with 100 μM ABA for 4 h; h: stomata before treatment with ABA; j: the CaMV 35S (pCAMBIA1301 vector) transformants as the positive control; k: non-transgenic Col-0 as the negative control. (b) GUS activity driven by the GbRLK promoter in above-ground tissues of transgenic Arabidopsis in response to ABA, PEG, NaCl and Verticillium dahliae. GUS activity from the CaMV 35S (pCAMBIA1301 vector) transformants served as the control. Data are mean and standard deviations of three replicates. The numbers below the bars indicate the -fold changes in GUS activity. Standard deviations (bars) are indicated. Significance of the changes produced after each treatment was assessed using Student’s t-tests (*P < 0.05, **P < 0.01).