Plants cope with nutritional stress using newly discovered pathway

14th Jun 2011

Researchers from the Biotechnology and Biological Sciences Research Council (BBSRC) funded National Centre for Plant and Microbial Metabolomics at Rothamsted Research have increased our understanding of how plants use carbon under different conditions following the discovery of a new pathway and metabolites that represent a safety valve, activated under nitrate starvation.

Published in the leading scientific journal Proceedings of the National Academy of Sciences of the USA (PNAS) the research describes a fundamental mechanism by which plants offload carbon, bound for chlorophyll production, in response to nutritional stresses.

Chlorophyll, one of the key molecules of the photosynthetic process that sustains life on earth, contains both carbon and nitrogen and plants need to balance the metabolism of these vital constituents. The research team has discovered an overflow mechanism by which carbon-containing metabolites, destined for assembly into chlorophyll, via a route known as the 'terpenoid pathway', are diverted when nitrate levels are limiting. The overflow consists of the production of unusual molecules, called hemiterpenoids. In the work, the team utilised state of the art high throughput analytical instrumentation to monitor 'metabolite fingerprints' of roots and shoots of the model plant Arabidopsis, as it reacted to variation in nutrient supply.

The research provides fundamental knowledge of plant biochemistry in stress conditions. Engineering of the terpenoid pathway is being explored for many uses including the production of medicines and biofuels, and flux down this new pathway will be an important consideration in those endeavours. The hemiterpenoids themselves, which build up to quite high levels, have potential for exploitation as fuels or chemical building blocks for polymers. Parallels can be drawn between the new research and what is known about isoprene, a volatile hemiterpene and greenhouse gas emitted by many tree species under stress conditions.

Dr Jane Ward, leader of the research said "This research shows the power of metabolite fingerprinting to monitor metabolism and to discover new molecules and biochemical pathways. In this case we now have much-needed insight into nitrate sensing and carbon flow, fundamental processes that we need to understand for agricultural and industrial exploitation"

Prof Mike Beale, co-leader of the research said "Plants have developed a way of balancing solar powered carbon assimilation with the availability of nitrogen from the soil. This work brings new knowledge on the metabolic pathways involved in sustaining plant life, and opens up new opportunities in bioproducts as well as a means of investigating optimum nitrate usage, an important economic factor in crop production"

Professor Maurice Moloney, Director and Chief Executive of Rothamsted Research commented: "The exciting discoveries reported by Professor Beale and Dr. Ward in PNAS are an example of the knowledge that can be gained by the use of high-throughput metabolomics in plants. The findings are not only of fundamental value to plant science, but have intriguing implications for plant bioproducts and plant-based industrial biotechnology"

Professor Douglas Kell, BBSRC Chief Executive said "The BBSRC has taken a lead in funding large scale metabolomics facilities such as those at Rothamsted. Our success in improving crops and developing sustainable ways to produce food as well as biofuels and other chemicals from plants will be enhanced by research into plant metabolism. This particular discovery demonstrates the utility of taking a whole plant approach and makes an important contribution to our understanding of the fundamentals of how plants deal with the changing environment they find themselves in."

'Metabolomic analysis of Arabidopsis reveals hemiterpenoid glycosides as products of a nitrate ion regulated, carbon flux overflow' by Jane L Ward, John M Baker, Aimee M Llewellyn, Nathaniel D Hawkins and Michael H Beale, National Centre for Plant and Microbial Metabolomics, Plant Science Department, Rothamsted Research is published, this week in the online Early Edition of the Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1018875108).

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