Liquid Culture Systems for in vitro Plant Propagation

102 K. Y. Paek et al.
optimizing bioreactor types and culture parameters have been reported.
Although the main source of these inconsistencies may be due to species-to
species variations, careful consideration is needed in interpreting these
results. So, once the culture conditions have been established in a smallscale
bioreactor, cultures can be easily scaled up to large-scale (500-1000
litre bioreactors).
4.1 Secondary metabolites
The production of secondary metabolites using plant cells has been the
subject to extended research. In 1959 the first report on the large-scale
cultivation of plant cells appeared (Tulecke and Nickell, 1959). In the last
few years, much success has been achieved in the field of plant cell
fermentation and scaling up. Plant cells now can be cultivated in volumes up
to 75,000 litre (Rittershaus et al., 1989) (for reviews see Hisihimoto and
Azechi, 1988; Dornenburg and Knori, 1995; Bourgaud et al., 2001). Among
hundreds of secondary plant products that have been investigated with
undifferentiated cell cultures, shikonin, ginsenosides and berberine are
presently produced on a large scale and indeed these are the most successful
stories of an industrial scale-up linking plant cell culture with bioreactor
technology.
Although undifferentiated cell cultures mainly have been studied, a large
interest has been shown in hairy root and other organ cultures. Hairy roots,
once established, can be grown in a medium with low inoculum with a high
growth rate. Several bioreactor designs have been reported for hairy root
cultures taking into consideration their complicated morphology and shear
sensitivity (Giri and Narasu, 2000). The main problem associated with hairy
root cultures in bioreactors is the restriction of nutrient oxygen delivery to
the central mass of tissue results in a pocket of senescent tissue. Due to
branching, the roots form an interlocked matrix that exhibits a resistance to
flow. The ability to exploit hairy root culture as a source of bioactive
compounds depends on development of bioreactor system where several
physical and chemical parameters must be taken into consideration.
4.2 Micropropagation
Automation of organogenesis in a bioreactor has been advanced as a
possible way of reducing costs of micropropagation (Takayama and Akita,
1994; Leathers et al., 1995; Chakrabarty and Paek, 2002; Paek et al., 2001).
Organogenic plant progagules are cultivated intensively in bioreactors for
the end result of producing transplants for mass production. Intensive
cultivation of such structures as potato microtubers and bulblets of lily is