Salicylic Acid and Phospholipid Signaling - Salicylic Acid: Plant Growth and Development - page 38

However, when the content of vanillin was evaluated in the presence of neomycin,
there was attenuation of the SA-stimulated vanillin production. These results
suggest that the secondary messengers generated by PLC are involved in the
stimulation of the vanillin production.
This fact led us to investigate how the phospholipid signaling pathway regulates
the production of vanillin in response to SA. We evaluated the activity of phen-
ylalanine ammonia lyase (PAL), the first enzyme of the phenylpropanoid pathway
that leads to the production of capsaicinoids, phenylpropanoids and lignin (Chen
et al. 2001 ). This enzyme is a biochemical marker of secondary metabolism in
response to different types of stress or to plant growth regulators such as SA
(Maldonado et al. 2007 ).
Using a suspension of C. chinense cells as a model, the effect of SA on PAL
activity was studied. We found stimulation of PAL activity. However, this increase
is diminished when neomycin or U73122 was also present in the media. This result
might suggest that the secondary messengers generated by PLC may be modu-
lating the SA-stimulated vanillin production through the activation of key enzymes
of the biosynthetic pathway.
We therefore propose a signaling model in which SA is perceived by receptors
in the plasma membrane (Fig. 3 ). The perception of this signal results in a stim-
ulation of the enzymatic activity of PAL and the content of vanillin in the cell
suspensions of C. chinense. However, in the presence of PLC inhibitors (neomycin

Fig. 3 A hypothetical model of phospholipid signaling in response to SA. Our model proposes
that, in cell suspensions of C. chinense, secondary messengers regulate the production of vanillin.
SA salicylic acid, PIP 2 phosphatidylinositol 4,5-bisphosphate, IP 3 Inositol 1,4,5 triphosphate,
DAG diacylglycerol, PAL phenylalanine ammonia lyase, DGK Diacylglycerol kinase, PA

Phenylalanine, PC Phosphatidylcholine