Plant cells, aggregation

In addition to bulk liquid turbulence effects, suspended particles maybe involved in collisions with one another or with solid surfaces within the vessel. This phenomenon has been extensively studied in micro-carrier cultures [60] and appears to be significant at high concentrations [61]. Rosenberg [69] and Meijer [72] applied the approach of Cherry and Papoutsakis [60] to the study of collision phenomena involving spherical plant cell aggregates of 190 and 100 pm, respectively. In both cases it was concluded that for typical biomass concentrations, particle-particle interactions were of less significance than particle-impeller collisions. 

Mavituna, F. and J. M. Park, "Size Distribution of Plant Cell Aggregates in Batch Culture," Chem. Eng. J. 35 (1987) B9-B14. 

Mavituna, E and Park, J.M. (1987) Size distribution of plant cell aggregates... 

Prenosil, J.E. and Hegglin, M. (1990) Self-immobilized plant cell aggregates in a bioreactor system with low shear stress. Ann. N.Y. Acad. Sci., 613, 234-247. 

Plant cells tend to aggregate, and large aggregates pose problems in maintaining a supply of nutrients to all cells and in removing wastes. The development of bioreactors for plant cells will require an understanding of limitations on mass transfer in such aggregates. 

The perceived sensitivity of plant cells to the hydrodynamic stress associated with aeration and agitation conditions is typically attributed to the physical characteristics of the suspended cells, namely their size, the presence of a cell wall, the existence of a large vacuole, and their tendency to aggregate. Table 1 illustrates some of the differences between plant cells and other biological systems. Chalmers [19] attributed shear sensitivity in mammalian cultures at least in part to the fact that these cells occur naturally as part of a tissue, surrounded by other cells. The same is true for plant cells. The more robust microbial systems, on the other hand, exist in nature as single organisms or mycelial structures, very close to the forms they assume in submerged culture. 

Cone-and-plate viscometers have been employed to study shear effects in both suspended (e.g. [138]) and anchorage dependent [122] mammalian cells. These devices have the advantage of requiring only small sample volumes ( lml). However, they are generally inappropriate for plant cell suspensions due to the larger cell and aggregate sizes. 

Dunlop [18] proposed a model for sub-lytic effects in plant cells, based on the same principles, but including four properties postulated to be of particular importance in these systems, namely calcium ion flux, osmo-regulation, cell-cell contact/aggregation and stress protein expression. Of these factors, osmo-regulation (and its inter-relationship with the cell wall) and aggregation patterns, in particular, distinguish plant cells from mammalian cell systems. 

Schwann, the cell theory emerged.. cells are organisms and entire animals and plants are aggregates of these organisms arranged according to definite laws (Schwann, 1838). 

Bioreactor-based systems for mass production of anthocyanins from cultured plant cells have been described for several species.A highly productive cell line of Aralia cordata obtained by continuous cell aggregate cloning has, for instance, been reported to yield anthocyanins in concentrations as high as 17%i on a dry weight basis. However, to date economic feasibility has not been established in part because of some unique engineering challenges inherent in mass cultivation of plant cultures. 

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