Liquid Culture Systems for in vitro Plant Propagation

42 Anne Kathrine Hvoslef-Eide et al.
1. Introduction
Internationally, there is considerable interest in developing vegetative
propagation methods that could facilitate rapid propagation of elite material
(Preil, 1991; Takayama and Akita, 1994). Considering the cost of labour in
Western Europe, propagation in liquid culture, especially in bioreactors, is a
possible way to produce clonal propagules at a low cost. One of the
advantages of growing cell cultures in bioreactors is the opportunity to
control the oxygen supply accurately in the liquid. This communication
describes a self-constructed and self-built set of six identical bioreactors to
provide controlled experimental conditions for cell cultures.
The designed bioreactors are closed systems or so-called batch
bioreactors, which are the most frequently used s in biotechnological
productions (Siebel, 1992; Glick and Pasternak, 1998). Having identical
bioreactors provides the possibility to run factorial experiments to reveal
interactions between the experimental parameters. The aim of the
construction was to take advantage of experience from cell cultures grown in
commercially-available bioreactors and to construct a bioreactor with
exceptionally low shear forces, at the lowest possible price. The bioreactors
on the commercial market have been designed to provide optimal growth for
bacteria, yeast and, to some extent, plant cell cultures for secondary
metabolite production. When aiming to grow somatic embryos for largescale
propagation, the effect of shear forces is more critical than for cell
cultures for secondary metabolites. First, we designed a prototype, tested
this out, improved it and then built a set of six identical “improved”
bioreactors. There are two features with our bioreactors that make them
more gentle to the cultured plant cells than various commercial designs; (1)
the aeration system and (2) the stirring device. Both are designed to allow
slow, gentle movement of the suspension, without allowing cell settlement in
quiet zones in the bioreactors. So far, we have grown embryogenic cultures
of carrot (Daucus carota) (Nissen, unpublished results), Norway spruce
(Picea abies) (Kvaalen, 1997), birch (Betula pendula) (Hvoslef-Eide, 2000),
cyclamen (Cyclamen persicum) (Hvoslef-Eide and Munster, 1997, 1998) and
shoot cultures of Christmas begonia (Begonia x cheimantha) (Hvoslef-Eide,
unpublished results) in our bioreactors.
For a more general and comprehensive description of plant cell
bioreactor design than is provided in this article, see the book chapter by
Heyerdahl et al. (1995).