Liquid Culture Systems for in vitro Plant Propagation

Application of Bioreactor Design Principles 27
k S (cm/hr)
60
50
40
30
20
10
0
ks,required
0 0.05 0.1 0.15 0.2
Diameter (cm)
ks,available
Figure 2: Comparison of oxygen transport required for aerobic respiration and availability in
terms of the mass transfer coefficients calculated by equations 3 and 4.
The required mass transfer coefficient (ks,required) based on oxygen consumption
(BOD= 300 µmol O2 cm -3 (tissue)·hr -1 ) is calculated for cylindrical (�) and spherical (�) plant
tissues. The available mass transfer coefficient (ks,available) is calculated based on the
sedimentation rates that would result for a cylindrical (�) and a spherical (�) tissue (�tissue =
1.04 g ml -1 ).
4. Manipulating oxygen availability
Plant tissues (and embryos in particular) can cope with reduced oxygen
availability, therefore it is unclear what the physiological impact would be.
None the less, recognizing the physiological changes associated with oxygen
availability, it is useful to understand how availability can be controlled in
bioreactors. Referring to equation 3, the only parameter that can be readily
manipulated is the liquid dissolved oxygen concentration (C L ). Control of
CL is most easily discussed in terms of the limiting case where the bulk
media dissolved oxygen approaches its equilibrium value (C * ) as depicted in
figure 1. The equilibrium dissolved oxygen (D.O.) is dependent on
environmental conditions as follows: