Scientists discover new plant-bacterial symbiotic mechanism: may increase crop yields tropical soils
The growth of most plants depends on the presence of sufficient amounts of nitrogen contained in the soil. However, a family of plants, the legumes, is partially free of this constraint thanks to its ability to live in association with soil bacteria of the Rhizobium genus, capable of fixing nitrogen from the air. When these bacteria come into contact with their host plant, they trigger in the roots the formation and development of organs, termed nodules, where they continue to live. This close relationship is called symbiosis, which benefits both organisms involved: the plant supplies nutritive elements to the bacteria which in return pass on the nitrogen they have stored up.
These interactions improve crop yields of leguminous plants that are crucial for human diet (soybean, peas, ground nuts and so on), as animal feed (alfalfa, clover, sainfoin) and in the future as bioenergy feedstock. In addition, cultivation of legumes living in symbiotic association with bacteria can contribute to vegetation regeneration schemes on soils depleted in nitrogen owing to overexploitation, erosion or desertification. The plant cover thus formed can help achieve ecological restoration, by enriching the soils in nitrogen. However, the symbiotic processes studied predominantly concern the leguminous plants of temperate zones, very little those of the tropics.
Now a large team from the Institut de Recherche pour le Développement's Laboratoire des Symbioses Tropicales et Méditerranéennes and its partners (CIRAD, AGRO-M, INRA, University of Montpellier, with the participation of the Genoscope at Evry, the CEA, the DOE Joint Genome Institute, the University of Minnesota and the University of Missouri) has discovered [*French] a new symbiotic mechanism. The research is published in Science.
The findings are promising for future techniques for bringing these bacteria into association with different leguminous plants. It therefore becomes possible to increase agricultural production of a greater number of important plants, particularly in tropical zones where soil nitrogen deficiency is a serious handicap. The discovery may also result in agricultural techniques that allow cutting down the use of fertilizers.
Taking as model a symbiosis between a tropical aquatic legume, Aeschynomene, and Bradyrhizobium, bacteria of the Rhizobia family, they revealed a new mode of communication at molecular level between these two organisms. The bacteria of this original model have their own photosynthetic pathway, a unique property in the rhizobia. This special character confers on it the exceptional, rare ability to form nodules on the stems of its host-plant. The plant thus acquires the possibility of fixing much higher quantities of nitrogen than those usually measured in leguminous plants which have nodules only on their roots.
The researchers sequenced the genes of two bacterial strains of Bradyrhizobium, ORS278 and BTAi1, in order to find out their genetic make-up and identify the genes involved in this rather special form of symbiosis. These bacteria were found to have no nod genes, usually essential for nodulation:
energy :: sustainability :: bioenergy :: biofuels :: biomass :: biotechnology :: plant biology :: symbiosis :: nitrogen :: fertilizer :: tropics ::
Bradyrhizobium consequently appeared to use mechanisms that involved other genes. This surprising result calls into question the universally recognized model of molecular communication that initiates the rhizobia-legume symbiosis. This common model requires the presence of several nod genes which allow synthesis of the Nod factor, a compound elaborated by the bacterium which enables the plant to recognize it, by molecular recognition, thereby allowing the microorganism to penetrate inside the plant by the root hairs. The finding raises the question as to what signalling pathway Bradyrhizodium might use to gain entry to the plant and set off nodulation.
The first observation was that the bacteria did not penetrate the roots of its host-plant by the hairs. It took advantage of 'crack zones' comparable with wound areas. The set of results obtained from subsequent work, seeking to identify the genes involved in producing the unknown signal molecule that plays the role of Nod factor, prompted the team's hypothesis that a molecule similar to a plant hormone, cytokinin, could act in the mechanisms by triggering nodulation. The discovery of the nature of the signal molecule itself, which remains to be fully determined, brings a glimpse of future agricultural applications.
Many plants live in symbiosis with bacteria, but the mechanisms are known for only a small number of these interactions. The demonstration of alternative pathways capable of triggering the nodulation signal in certain rhizobia is promising for future techniques for bringing these bacteria into association with different leguminous plants. It therefore becomes possible to increase agricultural production of a greater number of important plants, notably in tropical countries, while cutting down the use of fertilizers.
The research was conducted in the Laboratoire des Symbioses Tropicales et Méditerranéennes, mixed research unit UMR 113 (IRD, CIRAD, AGRO-M, INRA, University of Montpellier), with the participation of the Genoscope at Evry, the CEA, the DOE Joint Genome Institute, the University of Minnesota and the University of Missouri.
Image: the bacterial photosystem based on Bradyrhizobiumis is placed in the nodules of Aeschynomene and gets activated because of the phytochrome. Credit: Eric Giraud, IRD.
References:
Eric Giraud et al., "Legume Symbioses: Absence of Nod Genes in Photosynthetic Bradyrhizobia" [*abstract], Science, 1 June 2007: Vol. 316. no. 5829, pp. 1307 - 1312, DOI: 10.1126/science.1139548, 2007.
Institut de Recherche pour le Développement: Le rôle des phytochromes pour la première fois déterminé chez des bactéries, Fiche 154 - May 2002.
Eurekalert: A new plant-bacterial symbiotic mechanism promising - July 15, 2007.
Article continues
These interactions improve crop yields of leguminous plants that are crucial for human diet (soybean, peas, ground nuts and so on), as animal feed (alfalfa, clover, sainfoin) and in the future as bioenergy feedstock. In addition, cultivation of legumes living in symbiotic association with bacteria can contribute to vegetation regeneration schemes on soils depleted in nitrogen owing to overexploitation, erosion or desertification. The plant cover thus formed can help achieve ecological restoration, by enriching the soils in nitrogen. However, the symbiotic processes studied predominantly concern the leguminous plants of temperate zones, very little those of the tropics.
Now a large team from the Institut de Recherche pour le Développement's Laboratoire des Symbioses Tropicales et Méditerranéennes and its partners (CIRAD, AGRO-M, INRA, University of Montpellier, with the participation of the Genoscope at Evry, the CEA, the DOE Joint Genome Institute, the University of Minnesota and the University of Missouri) has discovered [*French] a new symbiotic mechanism. The research is published in Science.
The findings are promising for future techniques for bringing these bacteria into association with different leguminous plants. It therefore becomes possible to increase agricultural production of a greater number of important plants, particularly in tropical zones where soil nitrogen deficiency is a serious handicap. The discovery may also result in agricultural techniques that allow cutting down the use of fertilizers.
Taking as model a symbiosis between a tropical aquatic legume, Aeschynomene, and Bradyrhizobium, bacteria of the Rhizobia family, they revealed a new mode of communication at molecular level between these two organisms. The bacteria of this original model have their own photosynthetic pathway, a unique property in the rhizobia. This special character confers on it the exceptional, rare ability to form nodules on the stems of its host-plant. The plant thus acquires the possibility of fixing much higher quantities of nitrogen than those usually measured in leguminous plants which have nodules only on their roots.
The researchers sequenced the genes of two bacterial strains of Bradyrhizobium, ORS278 and BTAi1, in order to find out their genetic make-up and identify the genes involved in this rather special form of symbiosis. These bacteria were found to have no nod genes, usually essential for nodulation:
energy :: sustainability :: bioenergy :: biofuels :: biomass :: biotechnology :: plant biology :: symbiosis :: nitrogen :: fertilizer :: tropics ::
Bradyrhizobium consequently appeared to use mechanisms that involved other genes. This surprising result calls into question the universally recognized model of molecular communication that initiates the rhizobia-legume symbiosis. This common model requires the presence of several nod genes which allow synthesis of the Nod factor, a compound elaborated by the bacterium which enables the plant to recognize it, by molecular recognition, thereby allowing the microorganism to penetrate inside the plant by the root hairs. The finding raises the question as to what signalling pathway Bradyrhizodium might use to gain entry to the plant and set off nodulation.
The first observation was that the bacteria did not penetrate the roots of its host-plant by the hairs. It took advantage of 'crack zones' comparable with wound areas. The set of results obtained from subsequent work, seeking to identify the genes involved in producing the unknown signal molecule that plays the role of Nod factor, prompted the team's hypothesis that a molecule similar to a plant hormone, cytokinin, could act in the mechanisms by triggering nodulation. The discovery of the nature of the signal molecule itself, which remains to be fully determined, brings a glimpse of future agricultural applications.
Many plants live in symbiosis with bacteria, but the mechanisms are known for only a small number of these interactions. The demonstration of alternative pathways capable of triggering the nodulation signal in certain rhizobia is promising for future techniques for bringing these bacteria into association with different leguminous plants. It therefore becomes possible to increase agricultural production of a greater number of important plants, notably in tropical countries, while cutting down the use of fertilizers.
The research was conducted in the Laboratoire des Symbioses Tropicales et Méditerranéennes, mixed research unit UMR 113 (IRD, CIRAD, AGRO-M, INRA, University of Montpellier), with the participation of the Genoscope at Evry, the CEA, the DOE Joint Genome Institute, the University of Minnesota and the University of Missouri.
Image: the bacterial photosystem based on Bradyrhizobiumis is placed in the nodules of Aeschynomene and gets activated because of the phytochrome. Credit: Eric Giraud, IRD.
References:
Eric Giraud et al., "Legume Symbioses: Absence of Nod Genes in Photosynthetic Bradyrhizobia" [*abstract], Science, 1 June 2007: Vol. 316. no. 5829, pp. 1307 - 1312, DOI: 10.1126/science.1139548, 2007.
Institut de Recherche pour le Développement: Le rôle des phytochromes pour la première fois déterminé chez des bactéries, Fiche 154 - May 2002.
Eurekalert: A new plant-bacterial symbiotic mechanism promising - July 15, 2007.
Article continues
Monday, July 16, 2007
Europe's Happy Planet Index: more carbon doesn't make us happier
The 'Happy Planet Index' (HPI) is an indicator of efficiency. Specifically, it compares the ultimate outcome of human endeavour – experienced well-being – with the ultimate input – planetary resources – at the national level. HPI poses two important questions: 1. Do high levels of resource consumption necessarily lead to high well-being outcomes? 2. Is it possible to achieve high levels of well-being without high levels of consumption?
In other words, do the gains in well-being achieved by the richest Western nations justify the massive additional strain that these countries place on the environment? The most straightforward way to see how countries in Europe are faring in terms of their resource consumption efficiency – and so to understand the unique perspective which HPI provides – is to walk-through the calculation step by step, comparing nations at each turn.
In its report titled The European Happy Planet Index, An index of carbon efficiency and well-being in the EU [*.pdf], the NEF looks back over the last 40 years and comes to surprising and worrying conclusions. In an age of climate change, when it is more important than ever that we use our resources efficiently, NEF's Index, published in association with Friends of the Earth, reveals that:
- Europe as a whole has become less efficient, not more, in translating fossil fuel use into relatively long and happy lives. In fact, the Index reveals that Europe is less carbon efficient now than it was in 1961.
- Across Europe people report comparable levels of well-being whether their lifestyles imply the need for the resources of six and a half, or just one planet like Earth. The message to politicians is that people are just as likely to lead satisfied lives whether their levels of consumption are very low or high and therefore they should not be afraid of policies to reduce demand.
- Countries that follow Anglo-Saxon socio-economic development pathways score worse than those that follow the Scandinavian model, which is far more focused on social solidarity and environmental sustainability.
To calculate the European Happy Planet Index, NEF first ranks countries separately for their carbon footprint, life expectancy and life satisfaction. Then countries are ranked for the efficiency with which their resource use translates into relatively long and happy lives. In the results a huge range of performance is revealed. This shows great potential to meet the challenge of reducing our collective carbon footprint, and to do so without damaging quality of life.Andrew Simms, NEF's policy director and head of the climate change programme says that "countries that have most closely followed the Anglo-Saxon, strongly market-led economic model show up as the least efficient. These findings question what the economy is there for. What is the point if we burn vast quantities of fossil fuels to make, buy and consume ever more stuff, without noticeably benefiting our well-being? We know that someone is just as likely to have high life satisfaction while living within their environmental means, as someone who recklessly over-consumes. So, what is preventing us from radically changing direction, and reaping the benefits? If Europe doesn't lead, India, China and Brazil will not follow."
The Index reveals that with regard to life expectancy and life satisfaction (happy life years):
- North European countries like Denmark, Switzerland, Iceland, Finland and Sweden do best in terms of life satisfaction.
- The UK comes a disappointing 15th in both league tables for life satisfaction and life expectancy. Contrasted with nations such as France and Germany this puts the UK just ahead in terms of life satisfaction, with Germany 16th and France 19th; but behind on life expectancy with France in 7th place and Germany just ahead in 14th.
- The so-called transition economies, such as Bulgaria, Lithuania, Latvia, and Romania do worst in both tables, differing only slightly in rank order.
Where the carbon footprint is concerned, a more interesting and less obvious picture begins to emerge:energy :: sustainability :: climate change :: fossil fuels :: renewables :: bioenergy :: natural resources :: carbon footprint :: life expectancy :: well-being :: happiness :: European Union ::
- While Luxembourg is by far the worst country for its carbon footprint per person (so bad in fact that we couldn't fit it on our scale), from a league of 30 nations the UK comes in fourth from the bottom. Finland and Estonia join the UK and Luxembourg at the bottom of the table as the other countries with worse consumption per head of population.
- The Scandinavian nations have some of the lowest per capita carbon footprints in Europe, despite also being amongst the richest and happiest nations. Some of the differences can be explained by access to domestically available renewable energy sources, but not all. Even wealthy, high consuming Switzerland has only the ninth largest footprint.
- Europe as whole is responsible for almost three times its fair, global share of carbon emissions.
When all the indicators are put together a picture of relative carbon efficiency and well being emerges, with very bad news for the UK.Iceland comes top of the European HPI. Scandinavian countries are the most efficient - achieving the highest levels of well-being in Europe at relatively low environmental cost with Sweden and Norway joining Iceland at the top of the HPI table. The UK comes 21st in the league of 30 countries and only transition economies, and Portugal, Greece, and Luxembourg do worse.
On current performance, Europe is not remotely close to navigating an economic course set to reach its desired location on climate policy. It needs to achieve a carbon footprint small enough to help prevent the planet warming by more than 2 degrees above pre-industrial levels. This requires cuts in emissions by industrialised nations of between 70 and 80 per cent by 2050 compared to 1990 levels according to Sir Nicholas Stern, author of the Treasury's influential report on the economics of climate change.
Worse still, as the European Happy Planet Index reveals, Europe is heading in the wrong direction, its carbon footprint still growing, and its level of carbon efficiency in terms of fuelling happy, long lives - lower than at any level in the last 40 years.
To reverse this trend, we need to look to the example of those European countries that are already the most efficient - some of the most socially progressive and technologically advanced nations anywhere in the world.
Innovative policies will need to be developed that significantly reduce per capita carbon footprints whilst enhancing well-being. This will require comprehensive action, but the key targets for policy makers are:
- Reducing consumption overall and setting legally binding targets for carbon reduction: Every European government needs to set legally binding targets for reducing carbon dioxide emissions, setting carbon budgets for 3-5 year periods, to ensure each country does its part in keeping global temperature increases below 2 degrees Celsius.
- Reducing inequalities: Inequalities - not just of income, but also of education, health and social opportunity - have a damaging impact on well-being. Governments should aim to halt and reverse rises in inequality, and provide more support for local communities to thrive.
- Support meaningful lives: It is time that European governments invested in and implemented national well-being accounts to inform policy making across government, ensuring that the impact of policy decisions on people's well-being is taken into account.
NEF and Friends of the Earth call on the UK and other European governments, and the European Commission to adopt this analysis and embrace and apply new measures of progress, like the HPI. Only then will we be equipped to address the twin challenges of delivering a good quality of life for all whilst remaining within life-supporting environmental limits.The impacts of global warming, both within the EU and around the world, means that we can no longer justify the marginal benefits reaped from our current high and inefficient levels of resource consumption. The price paid by future generations and people alive today in poorer countries, who have far fewer resources with which to adapt, is simply too great.
Europe needs urgently to find a new development path where good lives don't cost the earth.
References:
NEF: UK 21st in European league of carbon efficiency and well-being - July 16, 2007.
NEF and Friends of the Earth: The European Happy Planet Index, An index of carbon efficiency and well-being in the EU [*.pdf, registration required], July 2007.
Article continues
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