Bioprocess engineering
The large scale plant cell and tissue cultures have been
considered as an alternative source of biochemicals over the
last 40 years. Routien and Nickel received the first patent
for the cultivation of plant tissue in 1956 [1] and suggested
its potential for the production of secondary metabolites
[2]. Shortly after that time, the National Aeronautics and
Space Administration (NASA) started to support research
of plant cell cultures for regenerative life support systems.
Since early 1960s, experiments with plants and plant tissue
cultures were performed under various conditions of microgravity
in space (one-way spaceships, biosatellites, space
shuttles and parabolic flights, the orbital stations Salyut and
Mir) and accompanied by ground studies using rotating clinostat
vessels [3]. Growth, development and metabolism of
plant cells and tissues have been studied to improve our understanding
of plant cell biology and tissue physiology, and
derive criteria for bioprocess design [4].
Approaches to plant tissue bioprocess engineering
The term ‘Plant Tissue Culture’ in this paper refers to the
in vitro cultivation of any plant segment, whether a single
cell, a tissue or an organ [5]. There are five main types of
plant tissue cultures: (1) seedlings of plants (plant cultures),
(2) isolated embryos (embryo cultures), (3) isolated plant
organs (organ cultures), (4) explant cultures (tissue or callus
cultures), and (5) isolated cells or small aggregates dispersed
in liquid media (cell or suspension cultures).
The concept of using plant cell cultures is confined to
the production of valuable natural products such as pharmaceuticals,
flavors and fragrances, and fine chemicals – over
20 000 different chemicals are produced from plants, with
about 1600 new plant chemicals added each year. According
to an OECD report [6,7], plant derived drugs and intermediates
account for approximately 9–11 billion US$ annually
in the US alone.
Generally, theGenerally, the plant products of commercial interest are
secondary metabolites, which in turn belong to three main
categories: essential oils, glycosides and alkaloids. The essential
oils consist of mixture of terpenoids, which are used
as flavoring agents, perfumes and solvents. The glycosides
include flavanoids, saponins, phenolics, tannins, cyanogenic
glycosides and mustard oils, which are utilized as dyes, food
colors and medicinals (e.g., steroid hormones, antibiotics,
digitalis). The alkaloids are a diverse group of compounds
with over 4000 structures known; almost all naturally occurring
alkaloids are of plant origin. Alkaloids are physiologically
active in humans (e.g., cocaine, nicotine, morphine,
strychnine) and therefore of a great interest for pharmaceutical
industry [8].
Secondary metabolites are currently being obtained commercially
by extraction from whole plants. Large scale plant
tissue culture is an attractive alternative to the traditional
methods of plantation, as it offers two advantages: (1) controlled
supply of biochemicals independent of plant availability
(climate, pests, politics), and (2) well defined production
systems which result in higher yields and more consistent
quality of the product [9].
