Endoproteolytic activities in pea roots inoculated with the arbuscular mycorrhizal fungus Glomus mosseae and/or Aphanomyces euteiches in relation to bioprotection
S. Slezack et al., Endoproteolytic activities in pea roots inoculated with the arbuscular mycorrhizal fungus Glomus mosseae and/or Aphanomyces euteiches in relation to bioprotection, NEW PHYTOL, 142(3), 1999, pp. 517-529
Arbuscular mycorrhizal (AM) symbioses are known to play a role in increased
resistance of plants against soilborne pathogens. Mechanisms involved in t
his phenomenon are not yet well understood. This work investigates possible
roles of endoproteolytic activities in bioprotection of Pisum sativum root
s by Glomus mosseae against Aphanomyces euteiches. First, it is demonstrate
d that bioprotection occurs only in pre-mycorrhizal plants. Second, endopro
teolytic activities were analysed qualitatively and quantitatively during A
M symbiosis, in plants infected with either zoospores or mycelium of A. eut
eiches, and in mycorrhizal plants infected with the pathogen. In mycorrhiza
l symbiosis a progressive increase in endoproteolytic activities was observ
ed following root colonization by G. mosseae. By contrast, in roots inocula
ted with A. euteiches, a drastic increase in endoproteolytic activities was
observed which was correlated with the amount of pathogen occurring in roo
ts. Qualitative differences were seen among the endoproteolytic activities
detected in roots inoculated with zoospores or mycelium. The constitutive a
s well as mycorrhizal and pathogen-induced activities were further characte
rized as 'trypsin-like' serine endoproteases. Interestingly, in a situation
of bioprotection, only low levels of the activities normally associated wi
th the infection by A. euteiches were detected, suggesting that the synthes
is of these proteins is directly linked to the growth or virulence of the p
athogen.