The Mechanisms Of The Effects Of Shear Stress To Taxus Cuspidata In Suspension Culture

To well-understand the mechanism of the effect of shear stress to plant cell andthe mechanism of shear sensitivity of plant cell, some defined laminar shear fieldswere created for suspensions of Taxus cuspidata in a Couette-type shear reactor,which we made ourselves. The defense responses and signal transduction pathway ofshear signal were studied and a potential model for those results was proposed. Basedon those results, the mechanism of shear sensitivities of taxus cell suspensions indifferent growth phases was also investigated. From the work above we gained somevaluable results.1. Taxus cuspidate can answer 0.1Pa shear stress with defense responses. There have triphasic characteristics in 6 h for both intracellular H2O2 production and extra-cellular O2 production and the key enzyme responsible for oxidative bursts -· under the shear stress is primarily NADPH oxidase and the contribution of peroxidase for oxidative bursts was less. The O2 burst may account for the change -· of membrane permeability, and H2O2 burst plays an important role in inducing secondary metabolites such as the activation of phenylalanine ammonia lyase enzyme and phenolic accumulation.2. Studies focused on shear signal transduction showed that cytoskeleton are involved in the sense of shear stress with it action time of 5-15min and that G-protein, Ca2+ channel and PLC were proved to be necessary in shear signal transduction with their action time of 10-15 min,15-25 min and 20-25 min, respectively. It was also suggested that the action of G-proteins is the upstream event to Ca2+ influx and the action of PLC. The action of Ca2+ channel and PLC may be the two different pathways in transduction of the shear signal for they have a period of action time in common.3. Based on results above, a model is proposed to explain the defense responses and shear signal transduction in cultured T. cuspidata cells challenged with the shear stress.4. In testing suspension cultures of various ages, it was found that those cultures in the stages of exponential growth were more susceptible to shear stress than cultures in the lag phase. The reasons for their difference lied in the different recognition time and the speed for action.