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Abscisic acid negatively interferes with basal defence of barley against Magnaporthe oryzae.

Ulferts S, Delventhal R, Splivallo R, Karlovsky P, Schaffrath U - BMC Plant Biol. (2015)

Bottom Line: Interestingly, endogenous ABA concentrations did not significantly change after infection of barley with M. oryzae.Our results revealed that elevated ABA levels led to a higher disease severity on barley leaves to M. oryzae.This supports earlier reports on the role of ABA in enhancing susceptibility of rice to the same pathogen and thereby demonstrates a host plant-independent function of this phytohormone in pathogenicity of monocotyledonous plants against M. oryzae.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Physiology, RWTH Aachen University, 52056, Aachen, Germany. sylvia.ulferts@gmx.de.

ABSTRACT

Background: Plant hormones are well known regulators which balance plant responses to abiotic and biotic stresses. We investigated the role of abscisic acid (ABA) in resistance of barley (Hordeum vulgare L.) against the plant pathogenic fungus Magnaporthe oryzae.

Results: Exogenous application of ABA prior to inoculation with M. oryzae led to more disease symptoms on barley leaves. This result contrasted the finding that ABA application enhances resistance of barley against the powdery mildew fungus. Microscopic analysis identified diminished penetration resistance as cause for enhanced susceptibility. Consistently, the barley mutant Az34, impaired in ABA biosynthesis, was less susceptible to infection by M. oryzae and displayed elevated penetration resistance as compared to the isogenic wild type cultivar Steptoe. Chemical complementation of Az34 mutant plants by exogenous application of ABA re-established disease severity to the wild type level. The role of ABA in susceptibility of barley against M. oryzae was corroborated by showing that ABA application led to increased disease severity in all barley cultivars under investigation except for the most susceptible cultivar Pallas. Interestingly, endogenous ABA concentrations did not significantly change after infection of barley with M. oryzae.

Conclusion: Our results revealed that elevated ABA levels led to a higher disease severity on barley leaves to M. oryzae. This supports earlier reports on the role of ABA in enhancing susceptibility of rice to the same pathogen and thereby demonstrates a host plant-independent function of this phytohormone in pathogenicity of monocotyledonous plants against M. oryzae.

No MeSH data available.


Related in: MedlinePlus

Microscopic evaluation of the infection ofM. oryzaeon barley. Primary leaves of barley cultivar Ingrid were inoculated with a spore solution of M. oryzae isolate TH6772 (200,000 conidia mL−1) seven days after sowing. Leaves were harvested at 72 h p.i. and placed in 25% acetic acid in ethanol (v/v) until bleached. Thereafter, leaves were analyzed in water by bright field (A, B, D and E) or epi-fluorescence (C, F, G, H and I) microscopy. Category designations and labels correspond to the quantitative evaluation in Figures 2, 3 and 5C. app: appressorium; sechy: secondary hyphae; con: conidium; pap: papilla; gt: germ tube; epiHR: epidermal hypersensitive response; rmes: round-shaped mesophyll cells; cmes: collapsed mesophyll cells.
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Fig1: Microscopic evaluation of the infection ofM. oryzaeon barley. Primary leaves of barley cultivar Ingrid were inoculated with a spore solution of M. oryzae isolate TH6772 (200,000 conidia mL−1) seven days after sowing. Leaves were harvested at 72 h p.i. and placed in 25% acetic acid in ethanol (v/v) until bleached. Thereafter, leaves were analyzed in water by bright field (A, B, D and E) or epi-fluorescence (C, F, G, H and I) microscopy. Category designations and labels correspond to the quantitative evaluation in Figures 2, 3 and 5C. app: appressorium; sechy: secondary hyphae; con: conidium; pap: papilla; gt: germ tube; epiHR: epidermal hypersensitive response; rmes: round-shaped mesophyll cells; cmes: collapsed mesophyll cells.

Mentions: For hemi-biotrophic pathogens, such as Magnaporthe oryzae, less is known about the function of ABA in plant resistance. M. oryzae is a major fungal pathogen of rice (Oryza sativa L.) but is also able to infect other grasses or sedges including barley and wheat [11-13]. Koga and co-workers [14] found that ABA-treatment suppressed resistance of rice plants against M. oryzae. Interestingly, Wiese et al. [15] reported the opposite effect for the barley/powdery mildew (Blumeria graminis f. sp. hordei, Bgh) interaction. M. oryzae invades barley plants by direct penetration of epidermal cells which takes place after germination of conidiospores and formation of dark-pigmented appressoria. Growth of invasive hyphae into epidermal cells can happen without microscopically visible plant reaction (Figure 1A). However, also an autofluorescent papilla, a fortification formed at the inner site of the epidermal cell wall, may occur beneath appressoria (Figure 1B, C). Additional cytological reactions of barley cells attacked by M. oryzae are autofluorescent walls of epidermal cells (Figure 1D-G) or round-shaped and collapsed mesophyll cells, respectively (Figure 1H, I). The initial infection process, up to the formation of bulbous infection hyphae in the primarily attacked epidermal cell, resembles a biotrophic interaction. Later stages of infection, by contrast, are associated with cell necrosis which is visible at the cellular level as collapsed autofluorescent mesophyll tissue (Figure 1I) [16,17].Figure 1


Abscisic acid negatively interferes with basal defence of barley against Magnaporthe oryzae.

Ulferts S, Delventhal R, Splivallo R, Karlovsky P, Schaffrath U - BMC Plant Biol. (2015)

Microscopic evaluation of the infection ofM. oryzaeon barley. Primary leaves of barley cultivar Ingrid were inoculated with a spore solution of M. oryzae isolate TH6772 (200,000 conidia mL−1) seven days after sowing. Leaves were harvested at 72 h p.i. and placed in 25% acetic acid in ethanol (v/v) until bleached. Thereafter, leaves were analyzed in water by bright field (A, B, D and E) or epi-fluorescence (C, F, G, H and I) microscopy. Category designations and labels correspond to the quantitative evaluation in Figures 2, 3 and 5C. app: appressorium; sechy: secondary hyphae; con: conidium; pap: papilla; gt: germ tube; epiHR: epidermal hypersensitive response; rmes: round-shaped mesophyll cells; cmes: collapsed mesophyll cells.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4307682&req=5

Fig1: Microscopic evaluation of the infection ofM. oryzaeon barley. Primary leaves of barley cultivar Ingrid were inoculated with a spore solution of M. oryzae isolate TH6772 (200,000 conidia mL−1) seven days after sowing. Leaves were harvested at 72 h p.i. and placed in 25% acetic acid in ethanol (v/v) until bleached. Thereafter, leaves were analyzed in water by bright field (A, B, D and E) or epi-fluorescence (C, F, G, H and I) microscopy. Category designations and labels correspond to the quantitative evaluation in Figures 2, 3 and 5C. app: appressorium; sechy: secondary hyphae; con: conidium; pap: papilla; gt: germ tube; epiHR: epidermal hypersensitive response; rmes: round-shaped mesophyll cells; cmes: collapsed mesophyll cells.
Mentions: For hemi-biotrophic pathogens, such as Magnaporthe oryzae, less is known about the function of ABA in plant resistance. M. oryzae is a major fungal pathogen of rice (Oryza sativa L.) but is also able to infect other grasses or sedges including barley and wheat [11-13]. Koga and co-workers [14] found that ABA-treatment suppressed resistance of rice plants against M. oryzae. Interestingly, Wiese et al. [15] reported the opposite effect for the barley/powdery mildew (Blumeria graminis f. sp. hordei, Bgh) interaction. M. oryzae invades barley plants by direct penetration of epidermal cells which takes place after germination of conidiospores and formation of dark-pigmented appressoria. Growth of invasive hyphae into epidermal cells can happen without microscopically visible plant reaction (Figure 1A). However, also an autofluorescent papilla, a fortification formed at the inner site of the epidermal cell wall, may occur beneath appressoria (Figure 1B, C). Additional cytological reactions of barley cells attacked by M. oryzae are autofluorescent walls of epidermal cells (Figure 1D-G) or round-shaped and collapsed mesophyll cells, respectively (Figure 1H, I). The initial infection process, up to the formation of bulbous infection hyphae in the primarily attacked epidermal cell, resembles a biotrophic interaction. Later stages of infection, by contrast, are associated with cell necrosis which is visible at the cellular level as collapsed autofluorescent mesophyll tissue (Figure 1I) [16,17].Figure 1

Bottom Line: Interestingly, endogenous ABA concentrations did not significantly change after infection of barley with M. oryzae.Our results revealed that elevated ABA levels led to a higher disease severity on barley leaves to M. oryzae.This supports earlier reports on the role of ABA in enhancing susceptibility of rice to the same pathogen and thereby demonstrates a host plant-independent function of this phytohormone in pathogenicity of monocotyledonous plants against M. oryzae.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Physiology, RWTH Aachen University, 52056, Aachen, Germany. sylvia.ulferts@gmx.de.

ABSTRACT

Background: Plant hormones are well known regulators which balance plant responses to abiotic and biotic stresses. We investigated the role of abscisic acid (ABA) in resistance of barley (Hordeum vulgare L.) against the plant pathogenic fungus Magnaporthe oryzae.

Results: Exogenous application of ABA prior to inoculation with M. oryzae led to more disease symptoms on barley leaves. This result contrasted the finding that ABA application enhances resistance of barley against the powdery mildew fungus. Microscopic analysis identified diminished penetration resistance as cause for enhanced susceptibility. Consistently, the barley mutant Az34, impaired in ABA biosynthesis, was less susceptible to infection by M. oryzae and displayed elevated penetration resistance as compared to the isogenic wild type cultivar Steptoe. Chemical complementation of Az34 mutant plants by exogenous application of ABA re-established disease severity to the wild type level. The role of ABA in susceptibility of barley against M. oryzae was corroborated by showing that ABA application led to increased disease severity in all barley cultivars under investigation except for the most susceptible cultivar Pallas. Interestingly, endogenous ABA concentrations did not significantly change after infection of barley with M. oryzae.

Conclusion: Our results revealed that elevated ABA levels led to a higher disease severity on barley leaves to M. oryzae. This supports earlier reports on the role of ABA in enhancing susceptibility of rice to the same pathogen and thereby demonstrates a host plant-independent function of this phytohormone in pathogenicity of monocotyledonous plants against M. oryzae.

No MeSH data available.


Related in: MedlinePlus