Expression, activity of phenylalanine-ammonia-lyase and accumulation of phenolic compounds in Lotus japonicus under salt stress

In the present work the gene expression levels and enzyme activity of phenylalanine-ammonia-lyase (PAL) were investigated in plants of the model legume Lotus japonicus under control and stress conditions. PAL is the key enzyme of the phenylpropanoid pathway, a route that involves numerous branches that lead to the production of a wide range of metabolites that can play an important role in the response to different kind of environmental stress. Unexpectedly treatment with salt caused decrease in activity of PAL in roots and the expression of several isogenes for PAL was significantly altered in roots or leaves; although the most highly expressed one, LjPAL10, remained unaffected by the treatment. Changes in tissue contents of some phenolic compounds, namely increase of quercetin glycosides and decrease of some phenylpropanoids were observed. The possible physiological meaning of the accumulation of phenolic compounds together with the changes in PAL enzyme activity is discussed.