Figure 1.

MBP kinase activity upon initiation of Cf-4/Avr4-induced defense signaling. Cf-4/Avr4 tomato seedlings were grown at 33°C, after which defense signaling was induced by a shift to 20°C. Seedlings were subsequently sampled at intervals of 30 min over a period of 4 h (sample at t = 0 represents the harvest just before the temperature shift). Cf-4- and transgenic Avr4-expressing seedlings were combined (parents) and treated similarly. A, Protein extracts from the seedlings were analyzed using in-gel kinase assays with MBP as a substrate. In each lane, similar amounts of protein were loaded as shown by Coomassie staining of the Rubisco large subunit. B, MBP kinase activity represented by the 50-kD band was quantified by phosphor imaging and expressed as the percentage of the maximal activity determined per experiment, which was set to 100%. For each time point, the average activity (bars) of five independent experiments is presented and ses of mean (sem) are shown by error bars. [See online article for color version of this figure.]