Fig. 4.

Antagonistic effect of SA on PDF1.2 expression in JA biosynthesis mutants. a, b Northern-blot analysis of PR-1 and PDF1.2 transcript levels in 5-week-old Arabidopsis plants that were treated with 1 mM SA, 0.1 mM MeJA, or a combination of both chemicals. For details on the JA biosynthesis mutants used, see legend to Fig. 3. Mutant npr1 was used as a negative control for SA–JA cross-talk. Leaf tissue was harvested 24 h after treatment for RNA analysis. Equal loading of RNA samples was checked using a probe for 18S rRNA. c Quantification of the signal intensities of the Northern blots in a and b using a Phosphor imager. PDF1.2 transcript levels in the single MeJA treatments were set to 100%. Please note that the quantitative data displayed in c are quantifications of the corresponding signal intensities in a and b and thus do not contain error bars. The Northern-blot analyses have been repeated with similar results