Plant defense strategies which act against the plant pathogen attack are explained in short. The major plant defense strategies are 1) Oxidative burst 2) Phenolics 3) Hypersensitive response (HR) 4) Phytoalexins.

1. Welcome
Name : Harshvardhan Dattatraya Gaikwad

2. Defense Strategies
Oxidative Burst :
It involves generation of Reactive Oxygen Species (ROS), primarily
singlet oxygen 1O2, superoxide O2
-, H2O2 and OH free radicals, which
trigger gene expression, cross-linking of host cell wall and initiation of
later defense responses. The ROS can kill the micro organisms directly
at the site of infection, but they can kill host cells also. The ROS can
directly trigger the hypersensitive response and, therefore, regulation
of their concentration is important.

3. Phenolics
Resistant Varieties- high phenols
Shikimic acid Pathway, Acetic acid pathway
Common phenols- Pre existing, Conc. Not sufficient, synthesis and
accumulation
Phytoalexins
Chlorogenic acid present in potato when it is affected with
Streptomyces scabies, (scab) and Verticillium wilt.
The peel of mango contains a mixture of antifungal resorcinols.
Tannic acid protect tobacco plant from infn by tobacco mosaic virus.

4. Hypersensitive Response (HR)
The final stage of rapid defence response. It is characterized by rapid
localized cell and tissue death around the site of infection.
HR is expressed only as a result of specific recognition between plant
and pathogen. The pathogen remained confined to necrotic lesions.
The cells surrounding necrotic region are highly reacting and initiate
synthesis of antimicrobial compounds (phytoalexins) and signal
molecules i.e. salicylic acid that induces non specific, SAR against
subsequent infections.

5. Phytoalexins
Low molecular wt. antimicrobial compounds produced by plants in
response to infection.
Associated with HR
HR in minuets, phytoalexins accumulation takes hours.
Not translocated and non- persistant (indefinitely continuous).
Over 350 phytoalexins are known in over 100 plant species.
Ipomeamarone in Ipomea batata.
Orchinol in Orachis militaris. orchid