Figure 3.

Effects of harpin on the JA-, SA-, and ET-signaling pathways in Arabidopsis. A, Quantification of the hormones. Subsections a and b, Endogenous levels of free JA and SA. Subsections c and d, Amounts of ET released. B, The effects of harpin and known elicitors on expression of genes involved in the pathways. Subsections a to c, RT-PCR analysis of signaling regulatory genes, defense genes, and expansin genes. Subsection d, RNA gel-blot analysis to confirm RT-PCR results. In A, a solution containing 15 μg mL⁻¹ harpin (rectangles) or 15 μg mL⁻¹ EVP (triangles) was applied by spraying the seedlings (A, a–c) or by soaking seeds for 6 h before incubation on agar medium (A, d). Levels of JA, SA, and ET were quantified as described in the text based on fresh weight of tissues (A, a–c) or germinated seeds (A, d). The data points indicate means ± sd of results. In B, lower leaves of plants were sprayed separately with solutions containing the indicated compounds. Twelve hours later, or at the indicated times, RNA was extracted from untreated upper leaves. The constitutively expressed gene EF1α was used as a standard in the RT-PCR protocol. RT-PCR products of genes in B, a and b, were loaded to gel separately; products of genes in B, subsection c, were loaded in a mixture of equal amounts. In B, subsection d, harpin 12 and harpin 24 refer to leaf sampling at 12 and 24 hpt with harpin. Treatment with harpin resulted in increased expression of ETR1 and ERS1 encoding the ET receptors ERF1 and NPR1 that are required, respectively, for ET and SA signal transduction. Harpin did not induce expression of CTR1, which functions in the absence of an ET signal. Harpin also did not induce expression of COI1, which is required for JA signaling.