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Genomics and Applied Biology
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2012, Vol.3 No.3, 22
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resistant varieties and introduce the genes which confer
resistance.
Plant Tissue culture studies
Plant tissue culture techniques have become a powerful
tool for studying and solving basic and applied problems
in plant biotechnology (Villalobos, 1987). From the last
three decades micropropagation and other
in vitro
techniques have routinely used in horticulture and
agriculture for rapid mass multiplication of crop plants
(Dodds, 1991; Das et al., 1996). Effectual exploitation
of biotechnological approach such as somaclonal
variation, somatic hybridization and genetic transfor-
mation, rely on proficient and unswerving regeneration
systems.
A tissue culture system provides considerable quantities
of highly regenerable target tissue. Numerous protocols
for somatic embryogenesis and organogenesis from
callus have been established. But a swift callus
induction has been achieved from immature leaves and
immature inflorescences. Minimal genetic changes, has
been noticed in regeneration through axillary buds even
though it is utilized for plant multiplication (Hendre et
al., 1983; Taylor and Dukic, 1993). Indirect embry-
ogenic have been induced by going through callus or
undifferentiated mass of cells. This has been done by
taking leaf or floral parts as starting material also called
ex-plant (Bower and Birch, 1992; Gallo-Meagher and
Irvine, 1993; Snyman et al., 1996; Ingelbrecht et al.,
1999).
Callus cultures establishment and maintenance is a labor
demanding and the regenerated plants are ready for
green house planting in at least 36 weeks (Bower et al.,
1996). From cell, tissue and organ cultures, production
of somatic embryo-like structures may happen either
directly or indirectly (Reinert et al., 1977 and Warren
and Fowler, 1977). Physical separation of the globular,
heart and torpedo stages of embryogenesis has been
achieved through somatic embryogenesis, using glass
beads to screen the cultures. Somatic or asexual
embryogenesis is the production of embryo-like
structures from somatic cells, a process which can occur
directly from an explant or indirectly via a callus stage.
The resulting somatic embryos are independent bipolar
structures that can develop and germinate to form plants
in a manner analogous to their zygotic counterparts
(Ammirato, 1987). As described by many workers (Ho
and Vasil, 1983; Ammirato, 1987), the embryogenic
areas were compact, nodular and white and comprised
relatively small, thin-walled, richly cytoplasmic,
basophilic cells with prominent nuclei, whereas the
friable and yellow non-embryogenic calli consisted of
large, thick walled, highly vacuolated and irregularly-
shaped cells. Indirect somatic embryogenesis occurs
when the explant is exposed to an auxin, which causes
the formation of callus from which plantlets can be
regenerated (Ho and Vasil, 1983).
Organogenesis is complicated process involving cellular,
molecular and tissue level change in the metabolism.
The unorganized mass of cells differentiates into shoots
by undergoing modifications in the metabolic reaction
etc. It is necessary to study the metabolic change by
investigating glucose utilization pattern. However there
are no reports on C14 glucose uptakes studies in 3
organogenetic stages. During short term feeding the
highest glucose activity is observed in callus stage and it
declines as the tissue dedifferentiates into shoots.
Similar pattern is observed during long term exposure. It
indicates that C14 glucose utilization pattern depends on
the organogenetic stage and its requirements are higher
at the initial callus stage than in the completely
regenerative shoots.
Genetic transformation of crop plants via
Agrobacterium
Agrobacterium
mediated gene delivery method for
genetic transformation of plants is ineffective in
monocotyledonous crops, because of host range
specificity of
Agrobacterium
which is a bacterium of
dicotyledonous plants (Weising et al., 1988). Several
alternative approaches have been developed for
monocot transformation e.g. electroporation (Fromm et
al., 1986), silicon carbide fiber (Keappler et al., 1990),
polyethylene glycol (lorz et al., 1985) microinjection
(Crossway et al., 1986) and gene gun delivery system
(Klein et al., 1987). In dicots, gene transfer through
Agrobacterium is proficient than gene gun delivery