Plant cell lines differred greatly in the ability to withstand shear stresses. Using to-bacco cells and licorice cells as model plant cells, we studied the effects of shear stresses on the vi-ability of plant cells. Our experiments were carried out on a high shear rate Couette rheometerproviding homogeneous and constant shear stresses of laminar flow. The viability was determinedby TTC(2,3,5-Triphenyl tetrazolium chloride). The results were as follows. (1)The viability(V)dropped exponentially with time(t), namely V=Exp(-kt), (k>o is a constant). This meant thetenability of statistical homogeneity. (2)The value of k was a function of plant cells’ mechanicalproperties and the shear stress acting on the plant cells. The shear rate corresponding to k=o wasthe critical shear rate that the plant cells could withstand. It can be easily determinded by extrapo-lation. For 7-day-old tobacco cells, it was 1090 s~(-1) and for 9-day-old licorice cells, it was6566 s~(-1).(3)The plant cell suspensions were pseudoplastic fluids fitting τ=Kγ~n. For the tobacco cell sus-pension tested, n=O. 73, and for the licorice cellsuspension tested n=0. 7. Thus the critical shearstress for the tobacco cells was 25 dynes/cm~2 and for the licorice cells it was 80 dynes/cm~2. (4)One of their reasons for licorice cells to have greater tolerance to shear stresses than tobacaccocells may be the geometric features of the cells and the sizes of the cells. The licorice cells wererod-shaped, but the tobacco cells were spherical and larger than the licorice cells. Plant cell lines differred greatly in the ability to withstand shear stresses. Using to-bacco cells and licorice cells as model plant cells, we studied the effects of shear stresses on the vi-ability of plant cells. Our experiments were carried out on a high The results were as follows (1) The viability (V) dropped exponentially with time (t (2) The value of k was a function of plant cells’ mechanical properties and the shear stress acting on the plant The shear rate corresponding to k = o wasthe critical shear rate that the plant cells could withstand. It can be easily determinded by extrapolation. For 7-day-old tobacco cells, it was 1090 s ~ (-1) and for 9-day-old licorice cells, it was6566 s ~ (-1). (3) The plant cell suspension for the tobacco cell sus-pension tested, n = 0. 73, and for the licorice cellsuspension tested n = 0. 7. Thus the critical shearstress for the tobacco cells was 25 dynes / cm ~ 2 and for the licorice cells it was 80 dynes / cm ~ 2 (4) One of their reasons for licorice cells to have greater tolerance to shear stress than tobacaccocells may be the geometric features of the cells and the sizes of the cells The licorice cells were rod-shaped, but the tobacco cells were spherical and larger than the licorice cells.