Upregulation of phenylpropanoids and accumulation of cAMP during lead stress in Viola tricolor.

Abstract

Viola tricolor, a pseudometallophyte, gives rise to genetically and morphologically distinct metallicolous (M) and non-metallicolous (NM) ecotypes, though what metabolic processes underlie this adaptation has not been clarified. Both ecotypes were subjected to Zn (100 or 1000 mg/kg) or Pb (100 or 1000 mg/kg) over 3 or 7 days and examined through untargeted UPLC-MS metabolomics to investigate this gap. Roots showed extreme Pb accumulation that greatly exceeded Zn accumulation, as determined by atomic absorption spectrometry. A coordinated metabolic response exclusive to M plants at 1000 mg/kg Pb emerged from multivariate analyses (t-SNE/DBSCAN, sparse PCA, and cross-validated PLS-DA). Phenylpropanoid-pathway compounds predominated among spectral matched metabolites-flavonoids (kaempferol and apigenin derivatives, quercetin), coumarins (esculetin, cichoriin, prionanthoside), and the phenolic glycoside syringin-together with the lignan aketrilignoside B, sesquiterpenes (yedoensins A and B), triterpenoids, and sterols. Elevated cAMP was additionally observed in M roots at 3 days. We put forward that accumulation of specialized metabolites with antioxidant and metal-chelating properties constitutes the molecular foundation of Pb tolerance and adaptation in M V. tricolor. cAMP levels most likely reflect stress-associated nucleotide accumulation rather than a signalling mechanism.

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