Effects of plant growth regulators applied to the roots of hydroponically grown Taxus × media plants on the production of taxol and related taxanes

Abstract

Taxus × media cultivars/varieties ( n = 14) (purchased from Heasley's Nurseries, Butler, Pennsylvania) were screened for taxol, cephalomannine, and 10-deacetyltaxol content in their needles and roots. Overall, the mature roots of cv. Hicksii and var. Number 8 had the highest levels of taxol (424 and 427 mg/kg dry weight, respectively), while in the needles, the highest amounts were found in cv. Fieldii and var. Number 8 (231 and 249 mg/kg dry weight, respectively). Treating hydroponically grown cv. Hicksii plants with 100 μM gibberellic acid (GA) or 1000 μM chlorocholine chloride (CCC) decreased root growth by approximately 38, and 22%, respectively, while treating with 100 μM CCC increased root growth by 22%, compared to control plants. However, none of the treatments resulted in a greater than 9% increase in shoot growth compared to control plants, when evaluated over a 24 week period. Overall, the 100 μM CCC treatment promoted the highest root mass, root-to-shoot ratio, growth index, root volume, average root diameter, and total root length. The roots of plants treated with 1000 μM CCC and 10 μM ANC exhibited the highest amount of taxol, 332 ± 32 and 334 ± 34 mg/kg on a dry weight basis, respectively, compared to control plants (195 ± 32 mg/kg). However, none of the treatments had dramatic effects on the amount of taxol, cephalomannine, or 10-deacetyltaxol in needle and bark samples. In order to evaluate the overall effect of these treatments, the concentration of taxol, cephalomannine, and 10-deacetyltaxol found in the roots need to be expressed as a function of concentration and total root mass, because the different treatments significantly affected only root growth. Accordingly, the highest amounts were found in the roots of the plants treated with 100 μM CCC (430 μg per plant, compared to 308 μg per control plant). This increase merely represents the increased root growth observed with the 100 μM CCC treatment. CCC seems to have enhanced the process of secondary growth in the roots, as shown in scanning electron micrographs. Since the roots of plants treated with 100 and 1000 μM CCC contained higher concentrations of taxol, it appears that the process of secondary growth was responsible for the increase in taxol content.