Different amounts of cRNA (1.25, 2.5, 5.0, and 10 μg) prepared fromArabidopsis samples at 3 d after treatment with either BTH (A) or water (B) were used in this experiment to test if the signals were linear with the target amount. The results of the three PR genes from the first group classified in Figure 3(PR5, PR1, and PRX1, induced by BTH) and the results from an internal control UBQ4 are presented in this figure. Linear signals were detected from 1.25 μg to 10 μg of biotin-labeled cRNA for the three PR genes in the sample that was treated with BTH (A). In contrast, the expression levels ofPR5, PR1, and PRX1 in the control sample remained low (B). However, the expression signal of the internal control UBQ4 was always linearly related to the added target cRNA amount in both BTH-treated and control samples (A,B).