Tagged: nitrogen fixation

Chickpea plant

The response of mesophyll conductance to short- and long-term environmental conditions in chickpea genotypes

Mesophyll conductance to CO2 (gm), which regulates the diffusion of CO2 from substomatal cavities to the sites of carboxylation, is now recognized as a significant and variable limitation to photosynthesis. It is a combination of gaseous diffusion through the intercellular airspaces and diffusion in the liquid phase through the mesophyll cell walls, plasma membrane, cytosol and chloroplast envelope to chloroplast stroma, the site of carboxylation. gm has been shown to vary between genotypes of a number of species and with growth environments, including nitrogen availability, but understanding of gm variability in legume species is limited. Given the growing interest in gm as a breeding selection...

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A generic individual-based model (IBM) tool to disentangle plant interactions in forage legumes

Louarn and Faverjon develop a generic model to account for the growth and development of herbaceous legume species with contrasting above- and below-ground architectures. The individual-based model (IBM) integrates plant responses to light, water and nitrogen and solves competition for multiple resources in a spatially explicit environment. The IBM’s behaviour was assessed on a range of monospecific stands grown along three resource gradients. In addition to predicting the main density-dependent responses known about even-age plant populations, the IBM correctly anticipated plastic changes in the partitioning of dry matter, the N nutrition of legumes and the architecture of shoots and roots....

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A cross section of a Melilotus siculus root

Waterlogging tolerance in the forage legume Melilotus siculus

Messina (Melilotus siculus, Fabaceae) is a waterlogging-tolerant annual forage legume, but data were lacking for the effects of waterlogging on nodulated plants reliant on N2 fixation. Konnerup et al. find that plants inoculated with the appropriate rhizobia, Ensifer (syn. Sinorhizobium) medicae, formed nodules. Nodulated plants grew similarly well as plants fed NO3–, both in drained and waterlogged conditions. In waterlogged conditions the relatively high respiration rates of nodules relied on O2 movement via the secondary aerenchyma (phellem) in hypocotyl, roots and the outer tissue layers of nodules, which we demonstrated using microelectrodes.

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Pisum sativum

Elevated CO2 reduces nitrate inhibition of N2 fixation in Pisum

Additional carbohydrate supply resulting from enhanced photosynthesis under predicted future elevated CO2 is likely to increase symbiotic nitrogen fixation in legumes. Butterly et al. use free-air CO2 enrichment (FACE) to study field pea, Pisum sativum, growing under different levels of CO2 and N supply in a semi-arid cropping system and find that increasing N reduces nodulation at ambient CO2 but this inhibitory effect is less under elevated CO2. The results indicate that field pea may perform well in semi-arid agricultural systems under future CO2 concentrations irrespective of soil N status and subsequent gains in N input via enhanced N2 fixation...

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Invasive Mimosa does not share symbionts with native relatives

Invasive Mimosa does not share symbionts with native relatives

The legume genus Mimosa comprises approx. 500 species, most of which are native to the New World, with Brazil being the main centre of radiation, but ancient transoceanic dispersal resulted in the Indian subcontinent hosting up to six endemic species. Gehlot et al. examine the nodulation ability and rhizobial symbionts of two of these, M. hamata and M. himalayana, both from north-west India, and compare them with those of M. pudica, an invasive species. In contrast to all Brazilian Mimosa species so far examined, which are nodulated by rhizobia in the Betaproteobacterial genus Burkholderia, the symbionts of the two Indian...

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Medicago truncatula root with nodules infected with Nitrogen-fixing rhizobia.

Taking the Myc: evolution of the legume-rhizobia symbiosis

The legume family of plants can form a symbiosis with nitrogen-fixing bacteria known as rhizobia. In return for a supply of nitrogen compounds the plant provides sugars and houses the rhizobia in special organs called nodules (see figure). The development of the nodules and the infection of rhizobia into them are tightly regulated by the plant. Many genes are required for the establishment of a successful symbiosis so how did it evolve? The simple answer is that many of the genes were co-opted from their existing functions in symbioses with mycorrhizal fungi. The mycorrhizal symbiosis is ancient, appearing around 450...

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Image: Priester et al. 2012, PNAS.

Nanoparticles may compromise crops

Advances (ever an optimistic notion!) in technology take many forms and may have unanticipated consequences. Take, for example, the emerging discipline of nanotechnology, which works with structures that are intermediate between isolated atoms and bulk materials – in the range of 1–100 nm, and which often display physical attributes substantially different from those displayed by either atoms or bulk materials (e.g. Zhong Wang). Not surprisingly, therefore, concerns have been expressed about the effects that manufactured nanomaterials (MNMs) may have on human health or other biota if they ‘escape’ into the environment. John Priester et al.  examined the response of a major crop –...

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Image: US Environmental Protection Agency.

Old Year’s Honours in a fix?

As we all ponder the merits – or otherwise – of the UK’s monarch’s traditional – and annual! – New Year’s Honours’ List, let’s take a few minutes to pause and reflect on one of the most significant plant-based honours of the Old Year. Whilst we acknowledge that those who botanise (in its broadest meaning) are unlikely to get a Nobel Prize for their efforts, one worthy who managed to make the trip to Stockholm (Sweden) was Professor Ray Dixon (of the John Innes Centre [JIC], Norwich, UK). Sadly, the award was not a ‘Nobel’. It wasn’t even an Ig Nobel...

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Characterizing sub-optimal clover nodule phenotypes

Characterizing sub-optimal clover nodule phenotypes

Little is known regarding why some strains of rhizobia fail to form successful symbiotic associations with leguminous crop plants. Melino et al. compare incompatible (no N2-fixation) and poorly compatible (reduced N2-fixation) associations between four genotypes of clover (Trifolium spp.) and four strains of Rhizobium leguminosarum bv. trifolii and assess symbiotic effectiveness by a variety of measures. They find three major responses to incompatibility, namely failed bacterial endocytosis from infection threads into plant cortical cells, bacteroid differentiation that aborts prematurely, and a reduced pool of functional bacteroids as a result of premature senescence. Thus poor plant growth responses resulting from nodulation by...

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Image: David Monniaux/Wikimedia Commons.

Stormy times ahead

Sir John Beddington (Chief Scientific adviser to the UK Government) opened the UK Plant Science Federation (UKPSF) conference (18th and 19th April, 2012, John Innes Centre, Norwich, UK) with his ‘perfect storm lecture’ (a similar talk is available here). In that opening address he identified energy demands, food production issues, and dwindling freshwater supplies as the troublesome trio that conspire together to generate the perfect storm, and which are themselves exacerbated by global climate change and projected population growth. Not only did this set the tone for the conference, it also provided the background and context for many of the...

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