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Rice Genomics and Genetics 2013, Vol. 4, No. 4, 14-27
http://rgg.biopublisher.ca
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used for long term preservation of plant materials.
5.3.5 Encapsulation-dehydration
Encapsulation-dehydration is a valuable procedure for
various plant materials, including in vitro-grown shoot
tips and somatic embryos. In this method, the
synthetic seeds are treated with a high sucrose
concentration, dried down to moisture content
20%~30% (under airflow or using silica gel) and
subsequently frozen in liquid nitrogen (Fabre and
Dereuddre, 1990). This technique may prove
interesting in two situations- (1) for the materials
which are recalcitrant to standard freezing techniques,
(2) the seeds that the protection conferred by the beads
allows submitting the embedded material to
pretreatment conditions which would otherwise be
detrimental. It may be beneficial also if the
encapsulation allows to carryout rapid freezing, thus
avoiding the use of a programmable freezing
apparatus and simplifying the process. The drawback
of this procedure is that it is rather lengthy and
labour-intensive.
6 Achievements
Research on artificial seeds in field crops, especially
cereals is still in infancy. However, many workers
successfully encapsulating somatic and androgenic
embryos of cereal crops (Datta and Potrykus, 1989;
Suprasanna et al., 1996; Roy and Mandal, 2008). Brar
et al. (1994) emphasized the need for research on
artificial seeds in rice through embryogenesis and
outlined its impact on mass propagation of
true-breeding hybrids. Somatic embryogenesis can
also be used in the regeneration of genetically
transformed plants (Vicient and Martinez, 1998).
Subsequently those somatic embryos could be
economically and successfully propagated though
synthetic seed technology.
Rice is the world’s most important food crop and a
primary food source for more than one third of the
world’s population.
This crop has received
considerable attention in biotechnology research
progammes. Research in artificial seeds in rice scanty
and this technology through somatic embryogenesis
would offer a great scope for large-scale propagation
of superior elite hybrids (Brar and Khush, 1994).
Somatic embryos of rice have been encapsulated to
produce synthetic seeds (Suprasanna et al., 1996).
Suprasanna et al. (2002) studied the viability of
encapsulated embryos derived from five year old long
term culture of Oryza sativa cv. basmati 370. The
encapsulated embryos showed better conversion into
plantlets than non-encapsulated embryos. Xing et al.
(1995) prepared artificial seed from hybrid embryos of
japonica and javanica rice. The germination rate of
artificial seeds in sterile conditions was 15%~60% on
vermiculite and agar media. The induction of pollen
embryogenesis genetically differs from zygotic
embryogenesis, and the androgenic embryos, may be
used for synthetic seed production. Datta and Potrykus
(1989) encapsulated microspore-derived embryos of
barely and germination response was found to be high
(80%) and seedlings were more vigourous than that of
non-encapsulated embryos.
Arunkumar et al. (2005) repoprted the addition of
protectants, bavistin and streptomycin as constituents
of synthetic endosperm and found that there was no
negative effect on germination and conversion. They
also studied the conversion of synthetic seeds into
seedlings in hybrid rice and reported that the
application of self-breaking gel beads technology
increased the germination (52%) and conversion (47%)
of synthetic seeds. Kumar et al. (2005) reported that
the synthetic seeds of rice with artificial endosperm
constituents of MS nutrient, sucrose (3% w/v) 0.5
mg/L IAA, 0.5 mg/L NAA, 0.5mg/L BAP and
activated charcoal (1.25% w/v) gave maximum
germination rate of 30% by using somatic embryos at
globular stage as propagules. They also reported that
the inclusion of activated charcoal had enhanced the
germination to the maximum extent by increasing the
diffusion of gases, nutrients and respiration of
embryoids.
Roy and Mandal (2008) prepared synthetic seeds from
androgenic embryos, embryo-like-structures and
microtillers of indica rice var. IR 72 (Figure 3). The
results indicated higher germination in the beaded
embryos than the unbeaded embryos. The reduced rate
of germination of artificial seeds may be attributed to
the damage incurred while separating the embryos
from clusters and/or owing to adverse affects of