Agrobacterium rhizogenes-Mediated Transformation and Its Biotechnological Applications in Crops - Crop Improvement: New Approaches and Modern Techniques - page 24

annual bedding plants (Mayo 1987 ). Breeding strategies empowered by genetic en-
gineering will lead to the development of more useful and productive crops for
plant breeders. While transferring genes to plants for being resistant against dis-
eases and insects, they might have been affected in other ways having altered prop-
erties (Oono et al. 1987 ; Spena et al. 1987 ; Schmulling et al. 1988 ; Fladung 1990 ;
Smigocki and Hammerschlag 1991 ; Scorza et al. 1994 ). Legumes are not only pro-
viding a main source of protein and oil for human and animal nutrition but also
contributing to the biological fixation of nitrogen. Moreover, a better understanding
of plant-microbe interactions such as symbiotic nitrogen fixation, mycorrhizal as-
sociations, and legume-pathogen interactions can be possible with legume studies
(Chilton et al. 1982 ; Christey 2001 ). Studies on aspects of hairy roots in legumes
showed that proliferous root growth and abundant lateral branching are important
for improving nitrogen fixation (Cheng et al. 1992 ).
Most plant structures, such as the hypocotyl, leaf, stem, stalk, petiole, shoot tip,
cotyledon, protoplast, storage root, and tuber, have shown capacity to be infected
and genetically transformed by A. rhizogenes resulting in stimulation of hairy root
formation (Mugnier 1988 ; Han et al. 1993 ; Bajrovic et al. 1995 ; Arican et al. 1998 ;
Drewes and Staden 1995 ; Giri et al. 2001 ; Krolicka et al. 2001 ; Azlan et al. 2002 ;
Veena and Taylor 2007 ). Applications of plant biotechnology favor hairy-root cul-
tures because of their special properties such as fast growth, short doubling time,
ease of maintenance, and ability to synthesize a range of chemical compounds and
proteins. Hairy root cultures are usually able to produce the same compounds found
in wild-type roots of the parent plant, without the loss of concentration (Kim et al.
2002 ; Veena and Taylor 2007 ). Above all, hairy roots have an ability to regenerate
stable transgenic plants either by a process of somatic embryogenesis or adventi-
tious bud formation, so that genetically modified generations can be achieved (Spa-
no and Costantino 1982 ; Tepfer 1984 ; Han et al. 1993 ; Cho and Wildholm 2002 ).
It is also known that modification of the cell hormonal balances occurring in
response to infection causes root formation at the infected site (Gaudin et al. 1994 ;
Aarrouf et al. 2012 ). However, the response varies depending upon the strain and its
interaction with the plant. One of the most important advantages is that hairy root
formation can be used as a verification of transformation. The use of antibiotic re-
sistance markers in the development of transgenic plants is given rise to substantial
public attention because of their unknown effects (Christey 2001 ).
Hairy roots have been used for infection of bacteria, fungi and nematodes and
shown to successfully complete their life cycles (Cho et al. 1998 ; Collier et al.
2005 ). The resistance genes of nematode have been studied through using hairy
roots (Cai et al. 1995 ; Remeeus et al. 1998 ; Kifle et al. 1999 ; Hwang et al. 2000 ).
Development of plants using hairy roots have become of interest because of great
potential for building up tolerance to biotic stresses and abiotic stresses (Porter
1991 ). Hairy root cultures provide an advantage related with making possible the
analysis of the changes in enzyme activities and their isoenzyme patterns (Messner
and Boll 1993 ; Kärkönen et al. 2002; Talano et al. 2006 ).
A variety of dicotyledonous plants are susceptible to A. rhizogenes . As a result
of stable transformation, root cultures have been established from a range of spe-