Effect of Shear Stress on Secondary Metabolite Production in Taxus Plant Cell Culture

One major drawback of producing paclitaxel using plant cell culture is low and unstable yields. Thus, exploration of methods for increasing yield of paclitaxel in Taxus PCC is an ongoing field of research. When plant cells divide, they often form masses of cells called aggregates that remain connected through their cell walls. Previous research in the Roberts laboratory has shown that large cellular aggregates produce less paclitaxel than smaller aggregates, possibly due to decreased shear force. To this end, we sought to investigate mechanical shearing of aggregates as a method for decreasing average aggregate size, which could be a method of increasing paclitaxel production. The two aims of this project are the following: to determine how shear stress affects Taxus secondary metabolism, and to design a device for continual shearing of plant cell cultures.

Mechanical shearing had an inconclusive effect on aggregate size distribution, with only sheared, methyl jasmonate elicited cells having aggregates that decreased in size over time. All other treatments did not lead to a decrease in aggregate size distribution over time. Taxane quantification data showed that a combination of shearing and methyl jasmonate elicitation yielded the highest concentration of paclitaxel. Secondary metabolites, which are chemical compounds that are produced in response to stress, also increased with both shearing and elicitation. This suggests that shearing does not specifically upregulate production of taxanes, but more generally upregulates secondary metabolism as a whole. Finally, a continual shearing device was designed with the intent to later construct and study this device as an alternative to manual shearing with a pipette