Liquid Culture Systems for in vitro Plant Propagation

Development of photoautotrophy in Coffea 331
and mode and amount of aeration of the vessel (Solarova et al., 1995).
Therefore, we cultured cotyledonary stage coffee somatic embryos under
photoautotrophic conditions in different growing systems with the aim of
developing an optimized protocol for large-scale embryo-to-plantlet
conversion and growth system.
Pre-treated cotyledonary stage embryos were cultured under
photoautotrophic conditions (in sugar-free medium with CO2 enrichment in
the culture headspace and high PPF) in three different types of culture
systems to optimize the plantlet conversion and growth: i) Magenta vessel ii)
RITA-bioreactor (a temporary immersion system) modified for
photoautotrophic micropropagation, and iii) a newly developed bioreactor
with a temporary root zone immersion system (TRI-bioreactor). The design
of the TRI-bioreactor has been described by Afreen et al. (2002b). The
planting density for all the treatments was 2.4x10 3 plantlets per m 2 vessel
surface area.
After 60 days of culture, results revealed that, in the TRI-bioreactor,
almost 84% of the embryos produced plantlets, whereas in Magenta vessel
and in modified RITA-bioreactor the conversion percentages were 53% and
20% respectively (Afreen et al., 2002b). Embryos cultured in the TRIbioreactor
produced more vigorous shoots and normal roots than those
grown in modified RITA-bioreactor and in Magenta vessel (Figure 3). The
TRI-bioreactor grown plantlets exhibited a greater number of leaves and
larger leaf area per plantlet than those noted in the modified RITAbioreactor
and Magenta vessel. Maximum leaf, stem and root dry mass were
recorded in the plantlets grown in TRI-bioreactor (Afreen et al., 2002b). In
general, most of the growth variables of the plantlets grown in Magenta
vessel were marginally different from those grown in the modified RITAbioreactor.
The most remarkable difference observed among the treatments
was in the percentage of rooting. In the TRI-bioreactor, 90% of the plantlets
developed roots; some roots produced lateral roots (Afreen et al., 2002b). In
the modified RITA-bioreactor, the roots, which developed in few plantlets,
remained very small.
In general, the chlorophyll concentration based on the fresh mass of the
leaves was highest in the TRI-bioreactor grown plantlets (Afreen et al.,
2002b). In case of the Magenta vessel, both the chlorophyll a and b
concentrations of the leaves exhibited an intermediate value between those
of the TRI- and modified RITA-bioreactors. Among the treatments, the
highest net photosynthetic rate was observed in plantlets grown in TRIbioreactor
(Afreen et al., 2002b). The results clearly pointed out that, in this
treatment, the forced ventilation system provided the best condition
throughout the experiment for the assimilation of CO2 and also the high rate
of air exchange was promotive of the development of functional stomata.