The relationship between morphological development and accumulation of saponins in the root of Polygala tenuifolia Willd

The root of Polygala tenuifolia Willd. (Polygalaceae) is a well-known Chinese crude drug. The morphological development of roots with their dynamic accumulation of saponins in Polygala tenuifolia was investigated by anatomical, histochemical and phytochemical approaches. Histochemical results revealed that the secondary phloem was the main storage region of saponins. We took senegenin as an indicator compound to analyze the regularity of saponin accumulation. HPLC results showed that the average content of senegenin of different-year-old roots in the „skin areas“ (1.081%) including periderm and phloem was 16.01 times more than that in the xylem (0.072%). During the growth period from April to October, the percentage of senegenin content of different-year-old roots exhibited a contineous decreasing trend (from 0.899% to 0.836% to 0.667% to 0.651%) and the accumulation of senegenin was opposite to that of biomass accumulation (from1.540g to 2.865g to 8.840g to 11.41g). The length, diameter, thickness of the „skin areas“ and dry weight as well as the total senegenin content of roots increased most quickly from the second to the third growth year. The mid-ten days of August of the third year were the optimal time for collecting the roots (having total senegenin 71.12mg/plant). The results add data to the relationship between secondary metabolism and plant development, and provide scientific bases for determining the most appropriate period for harvesting the roots.