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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

Cultivar-specific differences in disease severity after ABA-treatment. Abscisic acid (20 μM) or mock-solution were sprayed onto seven-days-old primary leaves of barley cultivars Ingrid, Steptoe, Morex, Pallas, Golden Promise, Hannah and Sultan5. Inoculation with M. oryzae isolate TH6772 (200,000 conidia mL−1) took place one hour after treatment. Disease severity was evaluated six days after inoculation by counting blast lesions. Means and standard deviations of at least nine leaves per cultivar and treatment are shown. Significant differences between mock- and ABA-treatment were determined individually for each cultivar using t-test (p ≤ 0.05) and marked with an asterisk. The experiment was repeated twice with similar results.
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Fig4: Cultivar-specific differences in disease severity after ABA-treatment. Abscisic acid (20 μM) or mock-solution were sprayed onto seven-days-old primary leaves of barley cultivars Ingrid, Steptoe, Morex, Pallas, Golden Promise, Hannah and Sultan5. Inoculation with M. oryzae isolate TH6772 (200,000 conidia mL−1) took place one hour after treatment. Disease severity was evaluated six days after inoculation by counting blast lesions. Means and standard deviations of at least nine leaves per cultivar and treatment are shown. Significant differences between mock- and ABA-treatment were determined individually for each cultivar using t-test (p ≤ 0.05) and marked with an asterisk. The experiment was repeated twice with similar results.

Mentions: So far, all experiments on the influence of ABA in the pathosystem barley/M. oryzae were done solely with the cultivar Ingrid. It could not be excluded, therefore, that the observed response to ABA was a specific feature of this particular cultivar. To address this question, we extended the study to seven barley cultivars encompassing spring and winter varieties. All plants were sprayed with a 20 μM ABA solution seven days after sowing and inoculated with M. oryzae isolate TH6772. Disease symptoms developed on leaves of all cultivars, indicating a compatible interaction with the chosen pathogen isolate (Figure 4). Quantitative differences in the number of lesions per leaf were found on mock-treated plants which revealed that the cultivars exhibited different levels of basal resistance against M. oryzae. Thus, on cv. Ingrid on average only two to five lesions were found per leaf of mock-treated plants. The number of disease symptoms per leaf increased for ABA-treated Ingrid-plants to 26, which was the highest relative rise within this experiment (Figure 4). For Steptoe, Morex, Golden Promise, Hannah and Sultan5 the number of lesions on ABA-treated plants was twice as high as on mock-treated plants of the same cultivar (Figure 4). The cultivar Pallas was an exception in this regard, since the overall number of lesions on untreated plants was highest (62 lesions per leaf) and ABA-treatment did not further increase disease severity. The disproportionately higher numbers of lesions on cv. Pallas may indicate a compromised basal defence of this cultivar against M. oryzae isolate TH6772. In case this impairment affects a resistance pathway that is influenced by ABA, additional ABA would not lead to a further decline in resistance.Figure 4


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)

Cultivar-specific differences in disease severity after ABA-treatment. Abscisic acid (20 μM) or mock-solution were sprayed onto seven-days-old primary leaves of barley cultivars Ingrid, Steptoe, Morex, Pallas, Golden Promise, Hannah and Sultan5. Inoculation with M. oryzae isolate TH6772 (200,000 conidia mL−1) took place one hour after treatment. Disease severity was evaluated six days after inoculation by counting blast lesions. Means and standard deviations of at least nine leaves per cultivar and treatment are shown. Significant differences between mock- and ABA-treatment were determined individually for each cultivar using t-test (p ≤ 0.05) and marked with an asterisk. The experiment was repeated twice with similar results.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig4: Cultivar-specific differences in disease severity after ABA-treatment. Abscisic acid (20 μM) or mock-solution were sprayed onto seven-days-old primary leaves of barley cultivars Ingrid, Steptoe, Morex, Pallas, Golden Promise, Hannah and Sultan5. Inoculation with M. oryzae isolate TH6772 (200,000 conidia mL−1) took place one hour after treatment. Disease severity was evaluated six days after inoculation by counting blast lesions. Means and standard deviations of at least nine leaves per cultivar and treatment are shown. Significant differences between mock- and ABA-treatment were determined individually for each cultivar using t-test (p ≤ 0.05) and marked with an asterisk. The experiment was repeated twice with similar results.
Mentions: So far, all experiments on the influence of ABA in the pathosystem barley/M. oryzae were done solely with the cultivar Ingrid. It could not be excluded, therefore, that the observed response to ABA was a specific feature of this particular cultivar. To address this question, we extended the study to seven barley cultivars encompassing spring and winter varieties. All plants were sprayed with a 20 μM ABA solution seven days after sowing and inoculated with M. oryzae isolate TH6772. Disease symptoms developed on leaves of all cultivars, indicating a compatible interaction with the chosen pathogen isolate (Figure 4). Quantitative differences in the number of lesions per leaf were found on mock-treated plants which revealed that the cultivars exhibited different levels of basal resistance against M. oryzae. Thus, on cv. Ingrid on average only two to five lesions were found per leaf of mock-treated plants. The number of disease symptoms per leaf increased for ABA-treated Ingrid-plants to 26, which was the highest relative rise within this experiment (Figure 4). For Steptoe, Morex, Golden Promise, Hannah and Sultan5 the number of lesions on ABA-treated plants was twice as high as on mock-treated plants of the same cultivar (Figure 4). The cultivar Pallas was an exception in this regard, since the overall number of lesions on untreated plants was highest (62 lesions per leaf) and ABA-treatment did not further increase disease severity. The disproportionately higher numbers of lesions on cv. Pallas may indicate a compromised basal defence of this cultivar against M. oryzae isolate TH6772. In case this impairment affects a resistance pathway that is influenced by ABA, additional ABA would not lead to a further decline in resistance.Figure 4

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