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system but in monocots, transformation via
Agrobac-
terium
is limited (Elliot et al., 1998). In monocots for
gene transfer via Agrobacterium different successful
attempts have been made recently such as in rice (Park
et al., 1996), and banana (May et al., 1995).
Agrobacterium
present quite a lot of merits, such as
technical simplicity, nominal genome rearrangements in
transformants, low copy number and the capacity to
transfer long stretches of DNA. In maize plants,
bar
gene expressions at a high degree was reported
(Gordon-Kamm et al., 1990) and have integration of
approximately 20 copies of intact gene. Gene transfer
methods intricate in Poaceace and this may be due to the
lack of various cellular responses which are essential for
transformation (Potrykus, 1985). Protoplast regeneration
and
Agrobacterium
host range were the major
bottlenecks for the production of transgenic in many
crops and this problem has been solved by micr-
oprojectile mediated gene delivery system (Rathus and
Birch, 1992).
Genetic transformation of crop plants via
Gene bombardment
Microprojectile mediated genetic transformation open
up the ways which have blocked by the problem of
Agrobacterium
host range and protoplast regeneration
for production of transgenic plants. A boost up in
transient expression frequency has been observed in
some species and tissue types by bombarding target
tissue twice (Wang et al., 1988) but a reduction in
frequencies was observed in others (Kartha et al., 1989;
Reggiardio et al., 1991). This showed condition for gene
gun method should be optimized for each type of tissue.
The first report of transgenic production was published
by Bower and Birch (1992) and described the
applicability of micro-projectile, gene delivery system
for transformation of grass family in which embry-
ogenic callus could easily be established. To avoid,
inhibition in expression of introduced gene, a low copy
number is desirable but complex integration patterns are
commonly found in Microprojectile-mediated trans-
formation.
A low copy number of the introduced gene is enviable
for practical genetic engineering to avoid probable
tribulations of co-suppression of expression caused by
multiple gene copies (Smith et al., 1990). Transfor-
mation efficiency and frequency may be affected by
bombardment distance (Taylor and Vasil, 1991) and
velocity of the micro-projectile. These factors may
damage the plant tissue physically (Gambley, 1993).
Gene delivery methods have been employed in scutellar
tissues of maize, wheat and rice (Napoli et al., 1990;
Smith et al., 1990; Fromm et al., 1990; Gordon-Kamm
et al., 1990).
For micro-projectile mediated transformation embryo-
genic callus cultures are ideal targets because
regenerable cells are not extremely secured, and can be
arranged to occupy most of the target area. After
bombardment of scutellar tissue of immature embryos
(Christou et al., 1991) regeneration of transgenic plants
is a beautiful approach for cereals, which are propagated
by relatively large seeds.
Conclusions
Plant biotechnology presents considerable improvement
in almost every area of crop production with possible
profit for farmers, industries and consumers. The growth
in the world population, their demands for food and
clear consumer preference for environmentally
sustainable agriculture will extend biotechnology’s role
in food production. Successful applications of various
biotechnological tools offer great promise to crop plants
in future.
References
Ammirato P.V., 1987, Organizational events during somatic embryo-
genesis. In the series analytic: Plant tissue and cell culture/edited by
Green C.E., Somers D.A., Hackett W.P., and Biesboer D. D., Proceedings
of the VI
th
International Congress, August 3-8, 1986, University of
Minnesota, New York, pp.57-81
Beetham P.R., Kipp P.B., Sawycky X.L., Arntzen C.J., and May G.D., 1999,
A tool for functional plantgenomics: Chimeric RNA/DNA oligonuleotides
cause
in vivo
gene specific mutatios, Proc. Natl Acad. Sci. USA., 96(15):
8774-8778 http://dx.doi.org/10.1073/pnas.96.15.8774
Bower R and Birch R.G., 1992, Transgenic sugarcane plants via
microprojectile bombardment, The Plant J., 2(3): 409-416 http://dx.doi.
org/10.1111/j.1365-313X.1992.00409.x
Bower R., Elliott A.R, Potier B.A.M., and Birch R.G., 1996, High-efficiency,
microprojectile-mediated co-transformation of sugarcane, using visible or
selectable markers, Mol. Breed., 2: 239–249
Christou P., Ford T.L., and Kofron M., 1991, Production of transgenic rice
(
Oryza stiva
L) uplants from agronomically important indica and Japonica