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CHAPTER
2
REVIEW OF LITERATURE
2.1. Importance of transgenic resistance
Although fungicides, pesticides and insecticides have offered protection
against crops, reluctance to rely on chemicals is increasing because of environmental
and health concerns. In recent years, with the advent of recombinant DNA and tissue
culture technologies transgenic resistance against phytopathogens using antimicrobial
genes has been achieved. Development of transgenic resistance has the promise of
providing season-long protection against specific pathogens. Plant transformation
represents a powerful supplemental tool to conventional breeding programs that can
accelerate the development of elite varieties with disease resistance and good
agronomic characteristics (Muthukrishnan er ol., 2001).
2.2.
Pathogenesis-related proteins: Biological activity a n d function
Plants synthesize a variety of compounds when exposed to biological stress
viz., fungi, bacteria, viruses, insects and herbivores (Collinge and Slusarenko, 1987;
Linthorst, 1991). The inducible defense responses include the production of reactive
oxygen species (ROS), phytoalexins, cell wall components (callose, glycine or
hydroxyproline-rich
proteins)
and
other
specific group of
proteins called
pathogenesis-related (PR) proteins. The PR-proteins were identified initially
as
inducible proteins in leaf extracts of tobacco plants reacting hypersensitively to
tobacco mosaic virus infection
(Van
Loon, 1985;
Van
Loon, 1999). Five distinct
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