Figure 1.

Time-course of cGMP generation in Arabidopsis thaliana leaves in response to virulent and avirulent Pseudomonas syringae strains. Both strains induced distinct time dependent increase in cGMP levels that peaked at ≥2 hours with the avirulent strain causing a more rapid response. Leaves of four week old plants were pressure inoculated with 10⁶ cfu/cm² bacterial cells suspended in 10 mM MgCl₂ solution. Whole leaf tissue was removed at the indicated time points and frozen immediately in liquid nitrogen. Cyclic GMP was extracted from N₂ snap-frozen ground leaves using the trichloroacetic acid extraction procedure as detailed in the manual to the Amersham cGMP assay kit. Cyclic GMP concentrations were subsequently measured with the Amersham Biosciences cGMP[¹²⁵I] assay system kit (code RPA 525, Amersham Biosciences, Little Chalfont, UK) using the acetylation protocol. Error bar values represent the mean (+/- SEM; n = 3) and the data are representative of two independent experiments.