The role of the oxidative burst. transient production of reactive oxygen
species (ROS). such as superoxide anion (02'1 and hydrogen peroxide (H20Z). in
elicitation of hypersensitive reaction (HR) was investigated in bean (Phaseoll)s
vulgaris L. cv. Bronco) inoculated with compatible. wild type strain 0NT), or
incompatible strain (TnS mutant) of Pseudomanas syringae pv. phas8olicola
(Burkholder). Inoculation with the \NT strain caused water-soaked lesions. while Tn5
strain elidted HR necrosis started to appear 12 h post-inoculation. Biochemical parameters, such as highly increase of the conductivity
(el~rolyte leakage). which is a well-known indicator of permeability changes
assOciated with HR, was found in the incompatible beanJbacleria (Tn5 strain)
inleraction. The conductivity of this incompatible combination was early induced and
markedly' increased, which recorded 1.5 & 6.25-limes higher than the control at 4 &
32 h post-inoculation, respectively. Also, lipid peroxidation, which is a well-known
parameter of HR development, was mao beanJbaderia interaction. It recorded, approximately, 3-times higher than the control
treatment at 16. 20, & 24 h and almost 4-times at 32, 36 h post-inoculation. It was a highly reduction in the growth rate of the Tn5 bacterial strain as
compared to that in the compatible combination, \NT strain, in bean leaf tissues as a
resun of superoxide anion and hydrogen peroxide generation. Multiplication of Tn5
strain slighUy increased by 1.3 and 0.5109, however \NT strain increased by 4.6 and
5.6 log at 24 and 48 h post-inoculation, respectively. Either 02" or H,O, were highly significant generated in bean leaf tissues
infittraled with the incompatible, Tn5 bacterial strain. as compared with both, tissues
infiltrated with the compatible \NT strain or control, at all time detection. O{ level in
tissue, infiltrated with Tn5 strain, reached 320 & 464% of the controltteatment at e &
24 h, respectively, post-infiltration. However, H20, level recorded 311 & 540% of the
control values at 6 & 36 h, respectively post-infiltration. These results suggest that an oxidative burst consisting of, at least, Of' and
H202 occur during the hypersensitive defense response, and may be it is innuenced
in HR necrotization. as well as counteracted the bacterial multiplication in bean leaf
tissues.