Abstract
Part 1 concerns the effect of light intensity on the leaves of Gomphrena globosa, a C-4 plant. Plants were grown under three light intensities. The structure and function of the photosynthetic apparatus of newly matured leaves were examined by a number of techniques. These were electron microscopy, infra-red fluorescence photomicrography, dye (TNBT) reduction and ¹⁴CO₂ feedings. Contrary to conclusions from the literature, light intensity did not affect the membrane configuration of the chioroplasts. Metabolite levels seemed to vary with light intensity. With respect to its photosynthetic properties G. globosa seems to occupy an intermediate position in a range of other C-4 plants. Part 2 describes some aspects of the relationship between a grass, Paspalum notatum, and a bacterium, Asotobacter paspali which is found mainly on the root surface of the grass. These organisms form a nitrogen fixing association in South-Eastern and Central Brazil. Both were studied separately because of the difficulty of establishing the association in the laboratory. An apparatus was built in which photosynthesis and root function of P. notatum could be monitored. ¹⁴CO₂ was fed to the leaves and ¹⁴C appearing in the roots and root exudate was analyzed. P. notatum appears to exude sufficient substrate to support nitrogen fixation by A. paspali but the amount and nature of exudate proved difficult to ascertain. The association is found in acid soils but nitrogen fixation by A. paspali is inhibited by low pH. It was found that roots of P. notatum were able to neutralize increases in acidity in their environment. A low pH inhibited N₂[C₂H₂]-fixing activity of A. paspali grown in continuous culture at high and low concentrations of carbohydrate and oxygen. Other nitrogen fixing bacteria, e.g. Beijerinckia spp and Derxia gummosa, are found in relatively low numbers in the rhizosphere of P. notatum. Nitrogen fixation by A. paspali may be less prone to oxygen inhibition than it is in these other bacteria, thus allowing A. paspali to compete more efficiently for carbohydrate. It seems that A. paspali lives with P. notatum because of the favourable pH that is maintained in the root environment. The carbohydrate and oxygen concentration are probably also favourable for nitrogen fixation. How can the association be easily established in the laboratory? Before further research can be done, a way must be found to answer this question.
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Claims 10
Claim · model-written summary
Light intensity did not affect Gomphrena chloroplast membrane configuration.
- Taxon
- Gomphrena globosa
Gomphrena globosae1 - Treatment
- light intensitye0
- Outcome
- membrane configuration of the chioroplastse0
- Direction
- did not affecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“light intensity did not affect the membrane configuration of the chioroplasts”
t0“C-4 plants”
e1“the leaves of Gomphrena globosa”
Claim · model-written summary
Gomphrena metabolite levels seemed to vary with light intensity.
- Taxon
- Gomphrena globosaGomphrena globosae1
- Treatment
- light intensitye0
- Outcome
- Metabolite levelse0
- Qualifier
- seemed to varye0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Metabolite levels seemed to vary with light intensity”
t0“C-4 plants”
e1“the leaves of Gomphrena globosa”
Claim · model-written summary
Gomphrena photosynthetic properties appeared intermediate among C-4 plants.
- Taxon
- G. globosaGomphrena globosae0
- Outcome
- intermediate position in a range of other C-4 plantse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“G. globosa seems to occupy an intermediate position in a range of other C-4 plants”
t0“C-4 plants”
Claim · model-written summary
Paspalum roots appeared to exude sufficient substrate to support A. paspali nitrogen fixation.
Verbatim
e0“P. notatum appears to exude sufficient substrate to support nitrogen fixation by A. paspali”
t0“C-4 plants”
Claim · model-written summary
Paspalum roots neutralized increased environmental acidity.
Not reportedDirection
Verbatim
e0“roots of P. notatum were able to neutralize increases in acidity in their environment”
t0“C-4 plants”
Claim · model-written summary
Low pH inhibited nitrogen fixation by A. paspali in continuous culture.
Verbatim
e0“A low pH inhibited N₂[C₂H₂]-fixing activity of A. paspali grown in continuous culture at high and low concentrations of carbohydrate and oxygen”
t0“C-4 plants”
e1“P. notatum appears to exude sufficient substrate to support nitrogen fixation by A. paspali”
Claim · model-written summary
Beijerinckia spp. were found in relatively low numbers in the Paspalum rhizosphere.
- Taxon
- P. notatume0
- Interactor
- Beijerinckia sppBeijerinckiae0other
- Outcome
- Beijerinckia sppe0
- Direction
- relatively lowe0
Verbatim
e0“Beijerinckia spp and Derxia gummosa, are found in relatively low numbers in the rhizosphere of P. notatum”
t0“C-4 plants”
Claim · model-written summary
Derxia gummosa was found in relatively low numbers in the Paspalum rhizosphere.
- Taxon
- P. notatume0
- Interactor
- Derxia gummosa
Derxia gummosae0other - Outcome
- Derxia gummosae0
- Direction
- relatively lowe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Beijerinckia spp and Derxia gummosa, are found in relatively low numbers in the rhizosphere of P. notatum”
t0“C-4 plants”
Claim · model-written summary
A. paspali nitrogen fixation may be less oxygen inhibited than fixation by other rhizosphere bacteria.
Verbatim
e0“Nitrogen fixation by A. paspali may be less prone to oxygen inhibition than it is in these other bacteria”
t0“C-4 plants”
e1“P. notatum appears to exude sufficient substrate to support nitrogen fixation by A. paspali”
Claim · model-written summary
The authors inferred favorable root pH permits the A. paspali and Paspalum association.
Verbatim
e0“A. paspali lives with P. notatum because of the favourable pH that is maintained in the root environment”
t0“C-4 plants”