Some common signal transduction events are not necessary for the elicitor-induced accumulation of silymarin in cell cultures of Silybum marianum

Production and localization of hydrogen peroxide and nitric oxide in grapevine cells elicited with cyclodextrins and methyl jasmonate

The use of methyl jasmonate, alone or in combination with cyclic oligosaccharides such as cyclodextrins, has proved to be a successful strategy for increasing the production of trans-resveratrol in Vitis vinifera cell cultures. However, understanding the intracellular signalling pathways involved in its production would improve the management of grapevine cells as biofactories of this high-value natural product. The results obtained herein confirm the involvement of hydrogen peroxide and nitric oxide in cyclodextrins and methyl jasmonate-induced trans-resveratrol production in grapevine cell cultures. In fact, methyl jasmonate led to maximal intracellular levels of hydrogen peroxide and nitric oxide after 24 h of treatment, but extracellular hydrogen peroxide was only detected in the culture medium when grapevine cells were treated with cyclodextrins. The results derived from the cytochemical detection of H₂O₂ in elicited grapevine cell cultures also suggested that the combined treatment with cyclodextrins and methyl jasmonate not only increased the production of H₂O₂ but also released cell wall fragments with electron-dense deposits. Moreover, nitric oxide was localized in all the cellular compartments, particularly in the nucleus and cytoplasmic organelles, whereas hydrogen peroxide was mainly found in cytoplasmic areas close to the cell wall, and in the nucleoplasm.

Silymarin secretion and its elicitation by methyl jasmonate in cell cultures of Silybum marianum is mediated by phospholipase D-phosphatidic acid

The flavonolignan silymarin is released to the extracellular medium of Silybum marianum cultures and its production can be stimulated by the elicitor methyljasmonate (MeJA). The sequence of the signalling processes leading to this response is unknown at present. It is reported in this work that MeJA increased the activity of the enzyme phospholipase D (PLD). Treatment with mastoparan (Mst), a PLD activity stimulator, also enhanced PLD and caused a substantial increase in silymarin production. The application of the product of PLD activity, phosphatidic acid (PA) promoted silymarin accumulation. Altering PLD activity by introducing in cultures n-butanol (nBuOH), which inhibits PA production by PLD, prevented silymarin elicitation by MeJA or Mst and also impeded its release in non-elicited cultures. Treatment with iso-, sec- or tert- butanol had no effect on silymarin production. The exogenous addition of PA reversed the inhibitory action of nBuOH, both in control and MeJA-treated cultures. These results suggest that the enzyme PLD and its product PA mediate silymarin secretion to the medium of S. marianum cultures.

Elicitation of silymarin in cell cultures of Silybum marianum: effect of subculture and repeated addition of methyl jasmonate

Production of silymarin and the effect of the elicitor, methyl jasmonate (MeJA), was monitored in cell cultures of Silybum marianum over 4 years. Silymarin concentrations gradually declined after prolonged subculture, making the success of elicitor strategy limited in long-term cultures. The continuous presence of MeJA in cultures for an extended period was necessary for induction of silymarin accumulation. A repeated elicitor strategy was not a good option for improving silymarin productivity in batch cultures. Removal of medium from elicited cultures and addition of fresh medium avoided the toxic effects of elicitor accumulation, allowing the system to respond to a repeated MeJA treatment without loss of productivity.