Analysis of Symbiosis Between Medicago Truncatula and Sinorhizobium Meliloti

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1. This work aims to analyze the existence of both partner choice and plant sanctions in Medicago truncatula- Sinorhizobium meliloti symbiosis by performing split-root experiments with natural strains (Gubry-Rangin et al. 2010). Noë & Hammerstein (1994) described symbiosis as ‘biological market’ since the plants are able to exchange the nutrients with different species which will create the conflict. The strains with different fixation level in natural rhizobia populations were described by Miller & Sirois (1982) and Rangin et al. (2008). Bull & Rice (1991) and Simms & Taylor (2002) suggested that rhizobia symbiosis is likely explained by the partner choice model as the bacteria are not transmitted vertically between plant generations. In…show more content…
The bacterial fitness was then measured using different parameters including the number of nodules, biomass per nodule, and the number of rhizobia per nodule.
Figure Number What method(s) gave these data? What do these data show?
1(a) split-root experiment Measurements of aerial biomass obtained in the split-root experiment:
- The N2-fixing strain appears efficient in nitrogen fixation than non-fixing strain
1(b) split-root experiment Measurements of nodule number obtained in the split-root experiment:
- The nodule number was significantly higher in roots inoculated with the non-fixing strain than the N2-fixing strain. This supports the pre-infection partner selection.
- There are restrictions of nodule formation in the non-limiting side of the plant when one side of the plant is nitrogen deficient in order to maintain the optimal nitrogen content.
1(c) split-root experiment Measurements of nodule biomass per nodule obtained in the split-root experiment:
- The biomass per nodule significantly higher for the N2-fixing strain compared with the non-fixing strain
- The mean biomass per nodule was higher in the N2-fixing strain which indicates that M. truncatula plants might be able to limit the nodule development of inefficient strain in order to avoid wasting resources.
- In the mixed treatment, a significantly higher biomass per nodule was measured for the N2-fixing strain than the

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