Articles
LIQUID CULTURE SYSTEMS FOR PLANT PROPAGATION
Manual handling is required during conventional micropropagation.
Labour costs may represent 65-85 % of the total costs, and methods of automation can reduce costs.
Scaling-up in micropropagation can increase the number of explants handled and thereby decrease the labour costs and can be achieved in several different ways: 1) Homogenisation of plant tissue in blenders rather than manual cutting; 2) Automation through use of liquid cultures and bioreactors; and 3) Robotics.
This paper focuses on the use of two liquid systems: 1) Temporary immersion systems; and 2) Permanent submersion of the plant cells/tissue that requires oxygen supply (rotary shakers or bioreactors). Somatic embryos and shoot cultures can be grown in both liquid systems, embryogenesis possibly being the most suited for full automation through a synthetic seed scheme.
Inclusion of an automatic cutter would facilitate almost full automation of shoot cultures as well.
Both temporary immersion and bioreactor applications have been reported for several agricultural, horticultural or forest plants.
So far, commercial applications have been rather limited.
Temporary immersion systems range from being simple, home-made devices managing the ebb and flow of liquid medium through peristaltic pumps, to rather expensive sophisticated equipment.
Bioreactors have the additional challenge of oxygen supply.
The challenges of bioreactor cultures have been described in detail by Heyerdahl et al. (1995). This paper uses our own bioreactors as examples of rather sophisticated bioreactors built in Norway.
In 1992, the Department of Agricultural Engineering of the Agricultural University of Norway (NLH) constructed and built six identical, computer controlled two-litre bioreactors.
These were made according to specifications from the Plant Cell Laboratory and used for scaling up plant propagation in liquid cultures.
We were mainly interested in somatic embryogenesis, but also shoot cultures that could be scaled up in such vessels.
Our bioreactors have been used to cultivate carrot, birch, Norway spruce, cyclamen and begonia.
The paper will briefly describe the different liquid systems for an overview.
The NLH bioreactor system is described in more detail and some results presented.