Accumulation of Salicylic Acid and 4-Hydroxybenzoic Acid in Phloem Fluids of Cucumber during Systemic Acquired Resistance Is Preceded by a Transient Increase in Phenylalanine Ammonia-Lyase Activity in Petioles and Stems1

Abstract

Cucumber (Cucumis sativa) leaves infiltrated with Pseudomonas syringae pv. syringae cells produced a mobile signal for systemic acquired resistance between 3 and 6 h after inoculation. The production of a mobile signal by inoculated leaves was followed by a transient increase in phenylalanine ammonia-lyase (PAL) activity in the petioles of inoculated leaves and in stems above inoculated leaves; with peaks in activity at 9 and 12 h, respectively, after inoculation. In contrast, PAL activity in inoculated leaves continued to rise slowly for at least 18 h. No increases in PAL activity were detected in healthy leaves of inoculated plants. Two benzoic acid derivatives, salicylic acid (SA) and 4-hydroxybenzoic acid (4HBA), began to accumulate in phloem fluids at about the time PAL activity began to increase, reaching maximum concentrations 15 h after inoculation. The accumulation of SA and 4HBA in phloem fluids was unaffected by the removal of all leaves 6 h after inoculation, and seedlings excised from roots prior to inoculation still accumulated high levels of SA and 4HBA. These results suggest that SA and 4HBA are synthesized de novo in stems and petioles in response to a mobile signal from the inoculated leaf.

Induction of Phenolic Compounds in Wheat (Triticum aestivum L.) Tissue Cultures by Streptomycin

“…Similar results were previously obtained by Vaughn and Duke (1984). Smith-Becker et al (1998) reported that the activities of polyphenol oxidase, peroxidase and PAL were increased in plants treated with various abiotic and biotic inducers. However, Cvikrova et al (1999) concluded that the inhibition of phenylpropanoid metabolism stimulated cell division during the growth cycle of alfalfa suspension cultures.…”

The Relationship Between Basal and Induced Resistance in Arabidopsis

“…Similar results were obtained by graftings between nontransformed tobacco plants and transgenics exhibiting epigenetic cosuppression of the PAL gene encoding phenylalanine ammonia-lyase, causing a strongly reduced biosynthesis of SA (Pallas et al, 1996). Indeed, Smith-Becker et al (1998) demonstrated that upon primary infection of a single cucumber leaf, the accumulation of SA in phloem fluids was preceded by a transient increase in PAL activity in the stems and petioles. These results suggested that SA is synthesized de novo in stems and petioles in response to an early mobile signal from the inoculated leaf.…”

Identification of defence metabolites in tomato plants infected by the bacterial pathogen Pseudomonas syringae

“…Similarly, a rapid and transient induction of PAL activity was also observed in the necrotic reaction of cucumber plants against P. syringae pv. syringae infiltration (Smith-Becker et al, 1998), although in this 660 interaction, PAL activity correlated with an increment of phenolic 4-hydroxybenzoic acid. In two compatible interactions, cucumber/prunus necrotic ring spot virus and melon/melon necrotic spot virus, an induction of PAL gene expression was also observed, but occurred at later time points (Bellés et al, 2008).…”