Insolubilization of cell wall hydroxyproline-rich glycoproteins is a c
ommon plant defence response when plants are challenged with either pa
thogens or elicitors derived from pathogens.-h yeast elicitor that ins
olubilized cell wall extensin of suspension-cultured tomato cells was
purified by 80% ethanol precipitation of yeast extract followed by ani
on-exchange chromatography, gel-filtration chromatography and reverse
phase HPLC. MALDI/TOF-mass spectrum analysis of the purified elicitor
preparation generated one major peak at 410 +/- 1 Da. Elicitor activit
y was inactivated at 100 degrees for 10 min or after incubation with p
ronase. No loss of elicitor activity was observed after periodate trea
tment. Polyclonal antiserum raised against native tomato extensin was
used to demonstrate extensin insolubilization in vivo. Salt-elutabilit
y of extensin from tomato cells was dependent upon concentration and t
ime of incubation of the cells with elicitor. SDS-PAGE/western blottin
g of salt-eluted protein from elicited cells also demonstrated insolub
ilization of HRGPs in the cell wall. The elicitor was found to stimula
te cell wall peroxidase activity and extensin insolubilization in isol
ated tomato cell walls and in intact cells. The elicitor also induced
a transient oxidative burst which began after 5 min and was maximal af
ter 20 min incubation with the cells. Other typical plant defence resp
onses known to be triggered by elicitors, such as changes in H+, K+ or
Ca2+ fluxes, enhanced activities of lipoxygenase, phenylalanine ammon
ia lyase and superoxide dismutase, were not observed when tomato cells
were challenged with this elicitor. The Ca2+ channel blocker verapami
l did not prevent elicitor-induced extensin insolubilization in whole
cells. This study suggests that biochemical events, such as transient
oxidative burst and enhanced peroxidase activity, which accompany exte
nsin insolubilization involve the cell wall without any apparent plasm
a membrane participation. The above cell wall events maybe sufficient
to form the early plant defence responses to microbial challenge. (C)
1997 Elsevier Science. All rights reserved.