Abstract
Leaves of Sorghum bicolor were examined at 5 d and 14 d after inoculation with the N 2 -fixing endophytic bacteria Herbaspirillum seropedicae and Herbaspirillum rubrisubalbicans. Plants inoculated with H. rubrisubalbicans expressed symptoms of 'red stripe disease' i.e. red stripes along the secondary veins of the leaf blade close to the inoculation point and spreading up the leaves. Infected leaves showed dense colonization by H. rubrisubalbicans in regions showing red stripe symptoms at 5 d after inoculation. The infection was confined within the vascular system, in particular, the protoxylem and associated lacunae, which were often completely filled with bacteria, with some of the latter expressing nitrogenase. The bacteria were recognized using H. rubrisubalbicans-specific antibodies and immunogold labelling, which also showed that the antibody reacted with material on the surface of the bacteria, and that this mucus was released into the lumen of the xylem. At 14 d after inoculation, disease symptoms were slightly more severe, with both meta- and protoxylem being even more heavily colonized in parts of the leaf showing red stripes. However, a strong host defence response was also apparent at this stage, with gums lining the walls of the vessels and enclosing the bacteria, although the latter were still actively dividing. At the edges of visible disease symptoms, plant gums filled the xylem; bacteria had formed distinct colonies within these gums, with some of the colonies associated with the xylem walls. Plants inoculated with H. seropedicae either did not express the disease or showed very mild symptoms close to the inoculation point. In the latter case, H. seropedicae were localized within protoxylem vessels and the metaxylem was partly occluded with plant-derived gums. By contrast with H. rubrisubalbicans, H. seropedicae was also localized in leaves at 14 d without disease symptoms and did not always appear to elicit a host response, i.e. they colonized the walls of metaxylem, with the xylem vessels themselves remaining unoccluded and largely free of gums. The fine line separating plant pathogens, endophytes and symbioses is discussed in light of these results.
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Claims 14
Claim · model-written summary
H. rubrisubalbicans inoculation caused red stripe disease symptoms spreading along sorghum leaf veins.
- Taxon
- Sorghum bicolor
Sorghum bicolort0 - Organ / stage
- leaf bladee0
- Treatment
- inoculated with H. rubrisubalbicanse0
- Interactor
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse0pathogen
- Outcome
- symptoms of 'red stripe disease'e0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Plants inoculated with H. rubrisubalbicans expressed symptoms of 'red stripe disease' i.e. red stripes along the secondary veins of the leaf blade close to the inoculation point and spreading up the leaves.”
t0“Sorghum bicolor”
Claim · model-written summary
At five days, symptomatic sorghum leaf regions showed dense H. rubrisubalbicans colonization.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Organ / stage
- leavese0
- Interactor
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse0pathogen
- Outcome
- dense colonization by H. rubrisubalbicanse0
- Qualifier
- at 5 d after inoculatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Infected leaves showed dense colonization by H. rubrisubalbicans in regions showing red stripe symptoms at 5 d after inoculation.”
t0“Sorghum bicolor”
Claim · model-written summary
The infection was confined to sorghum vascular tissue, particularly protoxylem and lacunae often filled with bacteria.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Organ / stage
- protoxylem and associated lacunaee0
- Interactor
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse1pathogen
- Outcome
- infection was confined within the vascular systeme0
- Qualifier
- often completely filled with bacteriae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The infection was confined within the vascular system, in particular, the protoxylem and associated lacunae, which were often completely filled with bacteria, with some of the latter expressing nitrogenase.”
e1“dense colonization by H. rubrisubalbicans”
t0“Sorghum bicolor”
Claim · model-written summary
Some colonizing H. rubrisubalbicans bacteria expressed nitrogenase.
- Taxon
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse1
- Gene
- nitrogenasee0
- Outcome
- expressing nitrogenasee0
- Qualifier
- somee0
Verbatim
e0“with some of the latter expressing nitrogenase.”
e1“dense colonization by H. rubrisubalbicans”
Claim · model-written summary
Specific antibodies and immunogold labelling recognized H. rubrisubalbicans and detected antibody-reactive surface material.
- Taxon
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse0
- Outcome
- bacteria were recognizede0
- Qualifier
- the antibody reacted with material on the surface of the bacteriae0
Not reportedComparator
Verbatim
e0“The bacteria were recognized using H. rubrisubalbicans-specific antibodies and immunogold labelling, which also showed that the antibody reacted with material on the surface of the bacteria”
Claim · model-written summary
Bacterial surface mucus was released into the sorghum xylem lumen.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Organ / stage
- xyleme0
- Interactor
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse1pathogen
- Outcome
- mucus was released into the lumen of the xyleme0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“this mucus was released into the lumen of the xylem.”
e1“H. rubrisubalbicans-specific antibodies”
t0“Sorghum bicolor”
Claim · model-written summary
At fourteen days sorghum disease symptoms were slightly more severe.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Interactor
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse1pathogen
- Outcome
- disease symptomse0
- Direction
- slightly more severee0
- Qualifier
- At 14 d after inoculatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At 14 d after inoculation, disease symptoms were slightly more severe, with both meta- and protoxylem being even more heavily colonized in parts of the leaf showing red stripes.”
e1“H. rubrisubalbicans-specific antibodies”
t0“Sorghum bicolor”
Claim · model-written summary
At fourteen days both meta- and protoxylem in symptomatic sorghum leaves were more heavily colonized.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Interactor
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse1pathogen
- Outcome
- meta- and protoxyleme0
- Direction
- more heavily colonizede0
- Qualifier
- At 14 d after inoculatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At 14 d after inoculation, disease symptoms were slightly more severe, with both meta- and protoxylem being even more heavily colonized in parts of the leaf showing red stripes.”
e1“H. rubrisubalbicans-specific antibodies”
t0“Sorghum bicolor”
Claim · model-written summary
Sorghum showed a strong host defence response with gums lining vessels and enclosing bacteria at fourteen days.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Organ / stage
- vesselse0
- Interactor
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse2pathogen
- Outcome
- strong host defence responsee0
- Qualifier
- gums lining the walls of the vessels and enclosing the bacteriae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“However, a strong host defence response was also apparent at this stage, with gums lining the walls of the vessels and enclosing the bacteria”
e1“At 14 d after inoculation”
e2“H. rubrisubalbicans-specific antibodies”
t0“Sorghum bicolor”
Claim · model-written summary
H. rubrisubalbicans remained actively dividing despite the host defence response.
- Taxon
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse1
- Outcome
- still actively dividinge0
Verbatim
e0“although the latter were still actively dividing.”
e1“H. rubrisubalbicans-specific antibodies”
Claim · model-written summary
At symptom edges, sorghum gums filled xylem and enclosed distinct bacterial colonies, some associated with xylem walls.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Interactor
- H. rubrisubalbicansHerbaspirillum rubrisubalbicanse1pathogen
- Outcome
- plant gums filled the xyleme0
- Qualifier
- bacteria had formed distinct colonies within these gums, with some of the colonies associated with the xylem wallse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At the edges of visible disease symptoms, plant gums filled the xylem; bacteria had formed distinct colonies within these gums, with some of the colonies associated with the xylem walls.”
e1“H. rubrisubalbicans-specific antibodies”
t0“Sorghum bicolor”
Claim · model-written summary
H. seropedicae-inoculated sorghum had no disease or only very mild symptoms near the inoculation point.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Treatment
- inoculated with H. seropedicaee0
- Interactor
- H. seropedicaeHerbaspirillum seropedicaee0symbiont
- Outcome
- either did not express the disease or showed very mild symptomse0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Plants inoculated with H. seropedicae either did not express the disease or showed very mild symptoms close to the inoculation point.”
t0“Sorghum bicolor”
Claim · model-written summary
In mildly symptomatic sorghum, H. seropedicae occupied protoxylem vessels and metaxylem was partly occluded by plant gums.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Interactor
- H. seropedicaeHerbaspirillum seropedicaee0symbiont
- Outcome
- H. seropedicae were localized within protoxylem vesselse0
- Qualifier
- metaxylem was partly occluded with plant-derived gumse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In the latter case, H. seropedicae were localized within protoxylem vessels and the metaxylem was partly occluded with plant-derived gums.”
t0“Sorghum bicolor”
Claim · model-written summary
At fourteen days H. seropedicae also colonized symptomless sorghum leaves without consistently eliciting a host response, leaving vessels unoccluded and largely gum-free.
- Taxon
- Sorghum bicolorSorghum bicolort0
- Organ / stage
- walls of metaxyleme0
- Interactor
- H. seropedicaeHerbaspirillum seropedicaee0symbiont
- Outcome
- localized in leaves at 14 d without disease symptomse0
- Qualifier
- did not always appear to elicit a host responsee0
- Comparator
- H. rubrisubalbicanse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“By contrast with H. rubrisubalbicans, H. seropedicae was also localized in leaves at 14 d without disease symptoms and did not always appear to elicit a host response, i.e. they colonized the walls of metaxylem, with the xylem vessels themselves remaining unoccluded and largely free of gums.”
t0“Sorghum bicolor”
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