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Are polyamines directly involved in silymarin production in the milk thistle [Silybum marianum (L.) Gaernt]

Cacho, Margarita, Torres Domínguez, Alexis, Elena-Rosselló, Juana-A.
Plant cell, tissue, and organ culture 2010 v.103 no.3 pp. 361-368
Silybum marianum, medicinal plants, silymarin, cell suspension culture, cultured cells, polyamines, biochemical pathways, cell lines, putrescine, spermidine, metabolism, cell cycle, cell growth, cell division, temporal variation
The possible role of polyamines (PAs) in the regulation of silymarin (Sm) production in milk thistle [Silybum marianum (L.) Gaernt] cell suspension cultures was studied in a young cell culture line (H2 line) and in a synchronized cell line (>3 years; H1 line). The effect of two exogenous PAs, putrescine (Put) and spermidine (Spd), and a number of metabolic inhibitors (L-canavanine, DL-α-difluoromethylornithine, methylglyoxal-bis-guanylhydrazone, cyclohexylamine) on the production of Sm during the growth cycle were analyzed. The results suggest that PAs are not directly involved in the Sm synthesis pathway. In our cell culture system, Sm production and PA contents were determined by the age of the suspension culture cells: with increasing age, the suspension culture cells showed a decreasing capacity to reach the stationary phase during prolonged subculture that was associated with a decreased production of Sm, a steady increase in PA content, and a constant Put/Spd ratio. The synchronization of dividing cells from the S. marianum H1 line did not modify this behaviour. In young cell suspensions, maximum Sm production occurred in the stationary phase, concurrent with the cellular PA contents reaching their minimum value. At the start of the stationary phase, the high percentage of cells in the growth phases (G₀/G₁) and a transient increase in the Put/Spd ratio were accompanied by maximum Sm production and a blockade of cell division.