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Rice Genomics and Genetics 2013, Vol. 4, No. 4, 14-27
http://rgg.biopublisher.ca
21
for multiplication of genetically engineered plants
(transgenic plants). Transgenic plants require separate
growth facilities to maintain original genotypes may
also be preserved using somatic embryos followed by
preparation of synthetic seeds for multiplication or
further propagation. Multiplication of elite plants
selected in plant breeding programmes through
somatic embryos avoids the genetic recombination,
and therefore, does not warrant continued selection
inherent in conventional breeding, saving considerable
time and resources.
The putative transformed tissue may be regenerated
into plantlets. Regeneration of large numbers of
transgenic plants is quite difficult or sometime
impossible. The transformed plant can be used for
clonal propagation through somatic embryogenesis
followed by preparation of artificial seeds.
5.3 Germplasm conservation
Besides rapid and mass propagation of plants, the
artificial seed technology has added new dimensions
not only to handling and transplantations but also for
conservation of endangered and precious plant
propagules.
5.3.1 Conservation at low temperature
Germplasm conservation in clonal crops, particularly
rooted crops, tuber crops and trees associated with
many problems. Conservation through tissue culture,
after a period of time, it becomes necessary to transfer
to fresh media and the sub-culture is a repeated and
continuous process. Repeated sub-culture overtime
may reduce the morphogenic competence of
differentiated cultures (Lynch and Benson, 1991).
Therefore, new culture has to be regularly initiated
and characterized in order to maintain a regular supply.
This approach is highly tedious and costly. The
technology of synthetic seed production may help in
this regard. Storage of encapsulated embryos for a
considerable time allows preservation of valuable,
elite gremplasm. Many authors successfully stored
synthetic seeds at low temperature (4
℃
) for varying
periods (Datta et al., 1999; Madhav et al., 2002; Ipekci
and Gozukirmizi, 2003; Ahmed and Talukdar, 2005).
Pintos et al. (2008) also successfully stored synthetic
seeds of cork oak at 4
℃
for two months without
significant loss in conversion capacity. The hydrated
synthetic seeds could be stored using low temperature
for a few weeks (Redebaugh et al., 1986; Fujii et al.,
1989; Fujii et al., 1992). The capability of prolonged
storage was achieved when somatic embryos could be
dried to moisture content less than 20% (McKersei et
al., 1989).
5.3.2 Conservation in plant tissue culture room
The alginate coated beads, made by encapsulating
small propagules are excellent stable germplasm units.
Bhattacharyya et al. (2007) successfully stored
synthetic seed of Plumbago indica, a medicinal plant
at culture room conditions (22~24
℃
temperature and
in dark) for 3 months without significance reduction
of conversion ability.
5.3.3 Cryopreservation
Cryopreservation is commonly used technique for
long-term preservation of biological material. This can
be defined to the stepwise viable freezing of biological
materials (seed, planting materials, plant callus,
somatic embryos, synthetic seeds etc.) followed by
storage at ultra-low temperature, preferably at that of
liquid nitrogen (196
℃
). This process preserves
growth and biosynthetic potencies of biological
materials. It arrests all metabolic activities and
biological deterioration of cells, thus the material can
be preserved for longer period of time. Practically, it
can be stored on solid CO2 (-79
℃
), in deep freezers
(-80
℃
or above), in vapour phase of nitrogen (-150
℃
)
or in liquid nitrogen (-196
℃
). Cryopreservation is
considered as an ideal means of avoiding loss of
embryopgenic potential during repeated subcultures
and as a means of preventing the occurrence of
somaclonal variation during long-term maintenance of
embryogenic culture.
5.3.4 Encapsulation-vitrification
Encapsulation-vitrification is a new technique of
preservation of plant materials, which combines the
advantages of vitrification (rapidity of implementation)
and of emasculation-dehydration (ease of
manipulation of encapsulated explants) has been
established (Matsumoto et al., 1995). This method is
user-friendly and greatly reduce the time requires for
dehydration. Thus, the method is frequently is being