Early defence responses of cowpea (Vigna sinensis L.) induced by non-pathogenic rust fungi

Abstract

Abstract. In cowpea (Vigna s&ensis L.) leaves the pathogenic rust fungus Uromyces vignae and the non-pathogens U. appendiculatus and U. viciae-fabae developed similarly to give rise to more than 80% haustorial mother cells. Whereas U. vignae was able to sporulate, the nonpathogens were stopped either after formation of some haustoria (U. appendiculatus) or immediately after formation of haustorial mother cells (U. viciae-fabae).Approximately 30% of the cells in contact with haustorial mother cells of the two non-pathogens showed autofluorescence and deposition of phloroglucinol/HC1-positive material. The early defence reactions of V. sinensis include induction of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) and extracellular peroxidase (POD, EC 1.11.1.7) activity as early as 10h and 24h after inoculation, respectively. Probing Western blots with heterologous monospecific anti-PAL serum showed that pathogenesis-induced increases in enzyme activity are the result of de novo synthesis. Native polyacrylamide gel electrophoresis revealed the specific induction of two extracellular acidic POD forms in cowpea inoculated with the non-pathogens. Both PAL and apoplasmic POD activities were highest in U. viciae-fabae-, intermediate in U. appendiculatus-and low in U. vignae-inoculated or talcum-treated control plants. The timing of increasing PAL and extracellular POD activities in relation to deposition of lignin or lignin-like material in mesophyll cell walls indicates the involvement of lignification in the early defence of V. sinensis against biotrophic fungal parasites. Analysis of the substrate specificity of the inducible POD forms, separated and partially purified by chromatofocusing, showed that apoplasmic PODs preferentially oxidize the naturally occurring substrate coniferyl alcohol. These results support the assumption that POD-mediated lignification is involved in the expression of non-host resistance of cowpea to rust fungi. * To whom correspondence should be addressed Abbreviations: IWF = intercellular washing fluid; PAL = phenylalanine ammonia-lyase; p.i. = post inoculation ; POD = peroxidase; SDS-PAGE = sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Differential Effects of Phenylalanine Ammonia Lyase, Cinnamyl Alcohol Dehydrogenase, and Energetic Metabolism Inhibition on Resistance of Appropriate Host and Nonhost Cereal–Rust Interactions

“…In agreement with previous reports, treatment with AOPP and OH-PAS dramatically diminished PCD-based resistance of Ribari, but only OH-PAS slightly decreased resistance of L94+Rph7. In L94+Rph7, it may be that leaf rust led to a late phenolic accumulation that was insufficient to account for resistance, as was also described in the cowpea-cowpea rust fungus interaction (8). Indeed, in L94+Rph7, PCD was associated with large colonies similar to those of the susceptible control, indicating a late-induced cell death.…”

“…avenae (22). Similarly, in cowpea, nonpathogenic rust fungi elicited PAL activity and caused autofluorescence associated with cell death (8), while virulent pathogens caused no such effects.…”

Microscopic and Molecular Characterization of the Prehaustorial Resistance against Wheat Leaf Rust (Puccinia triticina) in Einkorn (Triticum monococcum)

“…Non-host resistance is usually accompanied by early H 2 O 2 production and metabolism as, e.g., in the pathosystem O. sativa - wheat stripe rust (Zhao et al, 2014). In cowpea infection with non-pathogenic rust fungi led to arrest of infection hyphae immediately after the formation of haustorial mother cells and autofluorescence, deposition of phloroglucinol/HCl-positive substances in plant cells contacting them as well as phenylalanine ammonia-lyase and extracellular peroxidase activity as early as 10 and 24 hai was detected (Fink et al, 1991). Also in the A. thaliana-coffee leaf rust (Hemileia vastatrix) non-host pathosystem fungal growth was arrested at an early stage of stomatal infection, the expression of Pr-, and peroxidase genes and several other defense-related genes was increased, and phenolic substances and callose accumulated at the infection site (Azinheira et al, 2010).…”

An Investigation into the Involvement of Defense Signaling Pathways in Components of the Nonhost Resistance of Arabidopsis thaliana to Rust Fungi Also Reveals a Model System for Studying Rust Fungal Compatibility

“…Although nonhost resistance expressed after the rust fungus has entered the plant's intercellular spaces involves active plant responses, some of which modify the surrounding plant cell walls (Fink et al 1991;Perumalla and Heath 1991), the signaling systems involved in their induction are unknown. This study exploits available Arabidopsis thaliana mutants and rust fungi to demonstrate differences in the nonhost signaling pathways from those involved in host resistance to Arabidopsis pathogens and to reveal an Arabidopsis-rust fungus system that could facilitate the study of compatibility to these economically important biotrophic pathogens, even though Arabidopsis currently has no available rust disease.…”