Cell division versus secondary metabolite production in Morinda citrifolia cell suspensions

Morinda citrifolia cell suspension cultures are capable of accumulating high levels of anthraquinones, but appear to display an inverse relationship between the rate of cell division and anthraquinone production: low auxin concentrations lead to a high anthraquinone production and a low growth rare while at high auxin concentrations the reverse was observed. NAA and 2,4-D both showed this effect although there was a difference with respect to the optimal concentration, 2,4-D being active at approximately a hundred-fold lower concentration than NAA. We studied the inverse relation between cell division and anthraquinone accumulation in two ways. First, batch cultures of Morinda citrifolia were treated with hydroxyurea, which almost completely inhibited cell division. The 2,4-D cultures still did not accumulate anthraquinones. Second, we compared continuous cultures grown in the presence of NAA or 2,4-D at the same cell division rates. Only the NAA culture accumulated anthraquinones. The overall high sugar content of the cells under the various cultivation conditions indicated that sufficient energy and carbon substrates were always present. The possible direct effect of auxins on the induction and activity of the pathways leading to anthraquinone production is discussed.