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DNA synthesis and fragmentation in bacteroids during Astragalus sinicus root nodule development
H Kobayashi1, M Sunako, M Hayashi
1Department of Biotechnology, Graduate School of Engineering, Osaka University, Suita, Japan.
Bioscience, Biotechnology, and Biochemistry
|May 2, 2001
Summary
Bacteroids in Astragalus sinicus nodules undergo DNA fragmentation when nutrient-depleted, indicating programmed cell death. This process is linked to bacteroid localization in vacuoles and occurs during nodule senescence.
Area of Science:
- Plant-microbe interactions
- Molecular biology
- Cellular processes in symbiosis
Background:
- Mesorhizobium huakuii subsp. rengei forms nitrogen-fixing symbiosis with Astragalus sinicus.
- Bacteroid differentiation and function are crucial for symbiosis efficacy.
- Understanding bacteroid fate, including DNA replication and fragmentation, is key to symbiosis regulation.
Purpose of the Study:
- To investigate DNA replication and fragmentation in Mesorhizobium huakuii subsp. rengei bacteroids within Astragalus sinicus nodules.
- To correlate DNA fragmentation with bacteroid localization and nodule development stages.
Main Methods:
- Histo- and cytochemical techniques were employed.
- DNA replication was assessed using 5-bromo deoxy-uridine incorporation.
- DNA fragmentation was measured using the TUNEL (TdT-mediated dUTP nick-end labeling) assay.
Main Results:
- DNA synthesis was observed in plant nuclei and bacteroids near the nodule meristem.
- Nutrient-depleted bacteroids in vacuoles showed DNA fragmentation signals.
- Bacteroids with DNA fragmentation were found in the cytoplasm of senescent nodule cells at 2 months post inoculation.
Conclusions:
- Nutrient depletion triggers DNA fragmentation in bacteroids, potentially via autophagy and vacuolar sequestration.
- Bacteroid DNA fragmentation is associated with nodule senescence.
- These findings shed light on programmed cell death mechanisms in symbiotic bacteria.