Studies on the glyphosate-induced amino acid starvation and addition of precursors on caffeic acid accumulation and profiles in adventitious roots of Echinacea purpurea (L.) Moench

Shikimate pathway leads to the production of several secondary metabolites including caffeic acid derivatives (CADs), phenols and flavonoids and its regulation is assumed to respond to the requirements for both the synthesis of protein and secondary metabolites. We tested the response of growth, accumulation of phenols, flavonoids, caffeic acid, CADs profiles and activities of shikimate dehydrogenase (SKDH; EC. 1.1.1.25), chorismate mutase (CM; EC. 5.4.99.5), phenylalanine ammonia lyase (PAL; EC. 4.3.1.5) to glyphosate-induced starvation and feeding of aromatic amino acids (l-phenylalanine and l-tryptophan) in adventitious root cultures of Echinacea purpurea. Feeding of l-phenylalanine enhanced the growth but the accumulation of phenols, flavanoids and caffeic acid was lower in comparison to the l-tryptophan fed cultures. The addition of l-tryptophan (0.5, 1 and 5 mM) resulted in an increase up to 56, 61, 84 % in phenol, 24, 12, 3 % in flavonoids and 86, 63, 39 % in total caffeic acid. When glyphosate was added, the growth and accumulation of secondary metabolites were suppressed massively. The addition of l-tryptophan to the media not only countered the deleterious impact of glyphosate but enhanced the growth and accumulation of secondary metabolites in root cultures. The activity of SKDH, CM and PAL induced in presence of l-tryptophan. However, l-phenylalanine addition resulted in increase and decrease of PAL and CM activity, respectively. The presence of glyphosate maximally induced the PAL activity but that could not be translated into higher accumulation of secondary metabolites as it suppresses the accumulation of its substrates i.e. aromatic amino acids. Among CADs, highest cichoric acid and chlorogenic acid was found in l-tryptophan (0.5 mM) which was 2.0 and 1.62 times more than the control treatments. We concluded that addition of l-tryptophan (indolic pathway precursor) and not the l-phenylalanine (phenylpropanoid pathway precursor) stimulate the growth and accumulation of secondary metabolites in adventitious root cultures of E. purpurea (L.) Moench.