January
2004
, Volume
17
, Number
1
Pages
118
-
123
Authors
Hubert H.
Felle
,
1
Almut
Herrmann
,
1
Stefan
Hanstein
,
1
Ralph
Hückelhoven
,
2
and
Karl-Heinz
Kogel
2
Affiliations
1Botanisches Institut I, Justus-Liebig-Universität, Senckenbergstraße 17, D-35390 Gießen, Germany; 2Interdisziplinäres Forschungszentrum für Umweltsicherung, Institut für Phytopathologie und Angewandte Zoologie, Justus-Liebig-Universität, Heinrich-Buff-Ring 26-32, D-35392 Gießen, Germany
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RelatedArticle
Accepted 23 September 2003.
Abstract
To investigate apoplastic responses of barley (Hordeum vulgare L.) to the barley powdery mildew fungus Blumeria graminis f. sp. hordei, noninvasive microprobe techniques were employed. H+- and Ca2+-selective microprobes were inserted into open stomata of barley leaves inoculated with Blumeria graminis f. sp. hordei race A6 conidia. Resistance gene-mediated responses of barley genotype Ingrid (susceptible parent line) and the near-isogenic resistant Ingrid backcross lines (I-mlo5, I-Mla12, and I-Mlg) were continuously monitored from 20 min to 4 days after inoculation. The main events were categorized as short-term responses around 2 h after inoculation (hai), intermediate responses around 8 and 12 hai, and long-term responses starting between 21 and 24 hai. Short-term responses were rapid transient decreases of apoplastic H+- and Ca2+ activities that lasted minutes only. Kinetics were similar for all genotypes tested, and thus, these short-term responses were attributed as nonspecific first encounters of fungal surface material with the host plasma membrane. This is supported by the observation that a microinjected chitin oligomer (GlcNAc)8 yielded similar apoplastic alkalinization. Intermediate responses are trains of H+ (increase) spikes that, being different in susceptible Ingrid and penetration-resistant I-mlo5 (or I-Mlg), were interpreted as accompanying specific events of papillae formation. Long-term events were massive slow and long-lasting alkalinizations up to two pH units above control. Since these latter changes were only observed with near-isogenic hypersensitive reaction (HR)-mounting genotypes I-Mla12 and I-Mlg but not with I-mlo5 or, to a smaller extent, with susceptible Ingrid, both lacking significant rates of HR, they were rated as cell death specific. It is concluded that apoplastic pH changes are important indicators of host-pathogen interactions that correlate with both the different stages of fungal development and the different types of host defense response.
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© 2004 The American Phytopathological Society