Acclimation of Leaf Nitrogen to Vertical Light Gradient at Anthesis in Wheat Is a Whole-Plant Process That Scales with the Size of the Canopy

Vertical leaf nitrogen (N) gradient within a canopy is classically considered as a key adaptation to the local light environment that would tend to maximize canopy photosynthesis. We studied the vertical leaf N gradient with respect to the light gradient for wheat (Triticum aestivum) canopies with the aims of quantifying its modulation by crop N status and genetic variability and analyzing its ecophysiological determinants. The vertical distribution of leaf N and light was analyzed at anthesis for 16 cultivars grown in the field in two consecutive seasons under two levels of N. The N extinction coefficient with respect to light (b) varied with N supply and cultivar. Interestingly, a scaling relationship was observed between b and the size of the canopy for all the cultivars in the different environmental conditions. The scaling coefficient of the b-green area index relationship differed among cultivars, suggesting that cultivars could be more or less adapted to low-productivity environments. We conclude that the acclimation of the leaf N gradient to the light gradient is a whole-plant process that depends on canopy size. This study demonstrates that modeling leaf N distribution and canopy expansion based on the assumption that leaf N distribution parallels that of the light is inappropriate. We provide a robust relationship accounting for vertical leaf N gradient with respect to vertical light gradient as a function of canopy size.In cereals, as in many crop species, nitrogen (N) nutrition is a major determinant in the elaboration of grain yield and quality (Lemaire and Millard, 1999; Lawlor, 2002; Hikosaka, 2005). N is involved in both meristematic and photosynthetic activities, with consequences on plant architecture and carbon acquisition and in fine on grain yield and protein concentration. Beside the total amount of N absorbed by the crop, the allocation of N among plant organs plays a key role in determining crop productivity and quality (Grindlay, 1997; Dreccer et al., 1998; Hikosaka, 2005).Light interception and leaf N content are the two main factors governing carbon assimilation at the leaf scale (Evans, 1989). For various species, both light and leaf N attenuate with cumulative leaf area index counted from the top of the canopy (Field, 1983; Hirose and Werger, 1987). Leaf N vertical gradients have been regarded as an adaptive response to the local light environment, maximizing canopy photosynthesis and N utilization efficiency (Hirose and Werger, 1987; Hikosaka et al., 1994; Drouet and Bonhomme, 1999), as N is largely contained in the assimilatory enzyme Rubisco. Theoretical studies indicated that leaf N maximizes canopy photosynthesis when it parallels the light gradient (i.e. when the light [K_L] and N [K_N] extinction coefficients are equal), considering that the leaf N gradient is “optimal” in accordance with the “optimization theory” (Field, 1983; Hirose and Werger, 1987; Anten et al., 1995b).Factors other than the photosynthetic photon flux density (PPFD) might be responsible for the observed leaf N distribution. For instance, the acropetal gradients of leaf age (Hikosaka et al., 1994; Hikosaka, 2005) and light composition (Rousseaux et al., 1999) are known to strengthen the leaf N gradient. However, the impact of each of these factors has been shown to be much less than that of the PPFD gradient (Werger and Hirose, 1991; Pons and de Jong-van Berkel, 2004), although for the grass species Brachypodium pinnatum other factors than light might be involved (Pons et al., 1993). At the molecular level, the process could be driven by the import of compounds such as cytokinins transported in the transpiration stream (Pons et al., 2001; Boonman et al., 2007). Although the actual N distribution usually follows the light gradient, in all studies it is less steep than the calculated optimal N profile maximizing canopy photosynthesis (Pons et al., 1989; Yin et al., 2003). Possible reasons for this discrepancy have been discussed in detail by Kull (2002). Sink-source relations and in particular the demand for N could modulate the light-leaf N relationship (Dreccer et al., 1998), but conflicting results have been reported regarding the effect of N availability on the light-leaf N relationship. While some authors found no effect of N availability (Sinclair and Shiraiwa, 1993; Milroy et al., 2001), others found that the N gradient relative to light (i.e. K_L/K_N) was steeper under low N (Hikosaka et al., 1994; Grindlay et al., 1995; Lötscher et al., 2003) or that the response of the light-leaf N relationship to N availability depended on the developmental stage (Dreccer et al., 2000). Interspecific differences in the light-leaf N relationship have also been reported and were related to differences in phenotypic plasticity (Aerts, 1996) or plant architecture (leaf stature and branching pattern; Anten et al., 1995a; Lötscher et al., 2003).Since canopy photosynthesis is dependent upon the leaf N gradient, it has been suggested that the pattern of leaf N distribution could be responsible for part of the genetic variability associated with the negative correlation between grain yield and protein concentration reported for various crop species (Dreccer et al., 1998). In wheat (Triticum aestivum), N accumulated before anthesis contributes 30% to 70% of grain N (Mi et al., 2000; Kichey et al., 2007). The efficiency of N translocation from the lower to the upper leaves may increase with the steepness of the N gradient, with only a negligible effect on canopy carbon gain integrated over the whole grain-filling period. This hypothesis is consistent with experimental studies based on a range of genotypes showing that, at a given grain yield level, grain protein concentration is positively related to the efficiency of N translocation either from the lower to the upper leaves (Wang et al., 2005) or from the leaves to the grains (Monaghan et al., 2001; Jukanti and Fischer, 2008). Only a few studies have investigated the intraspecific variability of the light-N relationship at the intraspecific level (Shiraiwa and Sinclair, 1993; Bindraban, 1999; Bertheloot et al., 2008; van Oosterom et al., 2010). For wheat, published analyses of the genetic variability of the light-leaf N relationship were limited to only two to five genotypes, and no genetic differences were found (Bindraban, 1999; Bertheloot et al., 2008).This paper focuses on the genetic variability of the vertical leaf N gradient with respect to light for wheat. Three main issues were investigated. What is the effect of N supply on the vertical distribution of leaf N? Does the distribution of leaf N with respect to light differ among genotypes? If the adjustment of leaf N to the light gradient varies with both the genotype and N supply, could this genetic and environmental variability have a unique ecophysiological determinant (driving variable)?These questions were addressed using 16 genotypes (Supplemental Table S1) covering a wide range of variation for N use efficiency (i.e. grain dry mass yield per unit of available mineral N from the soil and fertilizer), for grain protein concentration (Le Gouis et al., 2000; Foulkes et al., 2006; Gaju et al., 2011) and for the deviation from the negative correlation between grain yield and protein concentration (Oury et al., 2003). The 16 genotypes were grown in the field under two conditions of N supply (N− and N+ for low- and high-N treatments, respectively) in order to modulate crop N status at Clermont-Ferrand (CF) in France in two consecutive seasons (experiments CF07 and CF08). In addition, four of the 16 cultivars representing the variability observed for N utilization and N uptake efficiency were grown in the field under two conditions of N supply at Sutton Bonington (SB) in the United Kingdom in one season (experiment SB07). The distribution of leaf N was analyzed at anthesis. The first reason for this is that the distribution of both light and leaf N within the canopy is relatively stable from this phenological stage until almost the end of grain filling (Bertheloot et al., 2008). Whereas the canopy green area index (GAI) decreases dramatically during the grain-filling period, the structure of the canopy affecting light interception does not change significantly during that period. Both the vertical light and N distributions down the canopy are unchanged during most of the grain-filling period; therefore, the K_N-to-K_L ratio is constant during that period (Bertheloot et al., 2008). Similarly, Archontoulis et al. (2011) showed that K_N-to-K_L ratio is not modified during the vegetative and reproductive stages for field-gown sunflower (Helianthus annuus) crops. Therefore, as most of the final grain yield results from carbon assimilated after anthesis (Bidinger et al., 1977; Gebbing and Schnyder, 1999), the N distribution at anthesis is very relevant in terms of carbon assimilation and grain yield in wheat. A second reason is that the number and potential size of grains are determined around anthesis, which therefore appears as a critical stage in the formation of grain yield. A better understanding of the ecophysiological determinants of leaf N gradient at this phenological stage could consequently be crucial for improving wheat productivity and quality (Dreccer et al., 1998).     

Link between intestinal CD36 ligand binding and satiety induced by a high protein diet in mice

CD36 is a ubiquitous membrane glycoprotein that binds long-chain fatty acids. The presence of a functional CD36 is required for the induction of satiety by a lipid load and its role as a lipid receptor driving cellular signal has recently been demonstrated. Our project aimed to further explore the role of intestinal CD36 in the regulation of food intake. Duodenal infusions of vehicle or sulfo-N-succinimidyl-oleate (SSO) was performed prior to acute infusions of saline or Intralipid (IL) in mice. Infusion of minute quantities of IL induced a decrease in food intake (FI) compared to saline. Infusion of SSO had the same effect but no additive inhibitory effect was observed in presence of IL. No IL- or SSO-mediated satiety occurred in CD36-null mice. To determine whether the CD36-mediated hypophagic effect of lipids was maintained in animals fed a satietogen diet, mice were subjected to a High-Protein diet (HPD). Concomitantly with the satiety effect, a rise in intestinal CD36 gene expression was observed. No satiety effect occurred in CD36-null mice. HPD-fed WT mice showed a diminished FI compared to control mice, after saline duodenal infusion. But there was no further decrease after lipid infusion. The lipid-induced decrease in FI observed on control mice was accompanied by a rise in jejunal oleylethanolamide (OEA). Its level was higher in HPD-fed mice than in controls after saline infusion and was not changed by lipids. Overall, we demonstrate that lipid binding to intestinal CD36 is sufficient to produce a satiety effect. Moreover, it could participate in the satiety effect induced by HPD. Intestine can modulate FI by several mechanisms including an increase in OEA production and CD36 gene expression. Furthermore, intestine of mice adapted to HPD have a diminished capacity to modulate their food intake in response to dietary lipids.     

Molecular systematics in the genus Mucor with special regards to species encountered in cheese

The genus Mucor, a member of the order Mucorales, comprises different species encountered in cheeses. Although fungi play a fundamental role in cheese manufacturing and ripening, the taxonomy of many fungal species found in cheese is poorly defined; indeed, this is the case for Mucor spp. In the present study, we assessed the phylogenetic relationships among 70 Mucor strains, including 36 cheese isolates, by using a five gene phylogenetic approach combined with morphological analyses. Overall, at least six species of Mucor were identified among the cheese isolates including a possible new taxon. The present study also suggests that the genus Mucor comprises undescribed taxa and needs to be properly defined.     

Receptor protein tyrosine phosphatase sigma regulates synapse structure, function and plasticity

The mechanisms that regulate synapse formation and maintenance are incompletely understood. In particular, relatively few inhibitors of synapse formation have been identified. Receptor protein tyrosine phosphatase σ (RPTPσ), a transmembrane tyrosine phosphatase, is widely expressed by neurons in developing and mature mammalian brain, and functions as a receptor for chondroitin sulfate proteoglycans that inhibits axon regeneration following injury. In this study, we address RPTPσ function in the mature brain. We demonstrate increased axon collateral branching in the hippocampus of RPTPσ null mice during normal aging or following chemically induced seizure, indicating that RPTPσ maintains neural circuitry by inhibiting axonal branching. Previous studies demonstrated a role for pre-synaptic RPTPσ promoting synaptic differentiation during development; however, subcellular fractionation revealed enrichment of RPTPσ in post-synaptic densities. We report that neurons lacking RPTPσ have an increased density of pre-synaptic varicosities in vitro and increased dendritic spine density and length in vivo. RPTPσ knockouts exhibit an increased frequency of miniature excitatory post-synaptic currents, and greater paired-pulse facilitation, consistent with increased synapse density but reduced synaptic efficiency. Furthermore, RPTPσ nulls exhibit reduced long-term potentiation and enhanced novel object recognition memory. We conclude that RPTPσ limits synapse number and regulates synapse structure and function in the mature CNS.     

Strontium ranelate--a promising therapeutic principle in osteoporosis

Strontium ranelate (2g/day) appears to be a safe and efficient treatment of osteoporosis (OP), reducing the risks of both vertebral and non-vertebral fractures (including hip) in a wide variety of patients. Thus, the agent can now be considered as a first-line option to treat women at risk of OP fractures, whatever their age and the severity of the disease. A long-term treatment with strontium ranelate in OP women leads to a continued increase in bone mineral density at spine and hip levels, and a sustained antifracture efficacy. The mode of action of strontium ranelate involves a dissociation between bone resorption and formation, as the bone formation rate is increased and not influenced by the antiresorptive action of the agent. Strontium is heterogeneously distributed in bone tissue: it is absent from old bone tissue and is exclusively present in bone formed during the treatment. Total area containing strontium in bone tissue increases during treatment, although the focal bone strontium content is constant. Whatever the duration of treatment and the content of strontium in bone, the degree of mineralization is maintained in a normal range. Furthermore, no change at crystal level is detected up to 3 years of treatment.     

DE-Cadherin regulates unconventional Myosin ID and Myosin IC in Drosophila left-right asymmetry establishment

In bilateria, positioning and looping of visceral organs requires proper left-right (L/R) asymmetry establishment. Recent work in Drosophila has identified a novel situs inversus gene encoding the unconventional type ID myosin (MyoID). In myoID mutant flies, the L/R axis is inverted, causing reversed looping of organs, such as the gut, spermiduct and genitalia. We have previously shown that MyoID interacts physically with β-Catenin, suggesting a role of the adherens junction in Drosophila L/R asymmetry. Here, we show that DE-Cadherin co-immunoprecipitates with MyoID and is required for MyoID L/R activity. We further demonstrate that MyoIC, a closely related unconventional type I myosin, can antagonize MyoID L/R activity by preventing its binding to adherens junction components, both in vitro and in vivo. Interestingly, DE-Cadherin inhibits MyoIC, providing a protective mechanism to MyoID function. Conditional genetic experiments indicate that DE-Cadherin, MyoIC and MyoID show temporal synchronicity for their function in L/R asymmetry. These data suggest that following MyoID recruitment by β-Catenin at the adherens junction, DE-Cadherin has a twofold effect on Drosophila L/R asymmetry by promoting MyoID activity and repressing that of MyoIC. Interestingly, the product of the vertebrate situs inversus gene inversin also physically interacts with β-Catenin, suggesting that the adherens junction might serve as a conserved platform for determinants to establish L/R asymmetry both in vertebrates and invertebrates.     

Development of polymorphic microsatellite markers issued from pyrosequencing technology for the medicinal mushroom Agaricus subrufescens

The recently described procedure of microsatellite-enriched library pyrosequencing was used to isolate microsatellite loci in the gourmet and medicinal mushroom Agaricus subrufescens. Three hundred and five candidate loci containing at least one simple sequence repeats (SSR) locus and for which primers design was successful, were obtained. From a subset of 95 loci, 35 operational and polymorphic SSR markers were developed and characterized on a sample of 14 A.?subrufescens genotypes from diverse origins. These SubSSR markers each displayed from two to 10 alleles with an average of 4.66 alleles per locus. The observed heterozygosity ranged from 0 to 0.71. Several multiplex combinations can be set up, making it possible to genotype up to six markers easily and simultaneously. Cross-amplification in some closely congeneric species was successful for a subset of loci. The 35 microsatellite markers developed here provide a highly valuable molecular tool to study genetic diversity and reproductive biology of A.?subrufescens.     

From ApoA1 upregulation to BET family bromodomain inhibition: discovery of I-BET151

The discovery, synthesis and biological evaluation of a novel series of 7-isoxazoloquinolines is described. Several analogs are shown to increase ApoA1 expression within the nanomolar range in the human hepatic cell line HepG2.     

Multi-stemmed trees of Nothofagus pumilio second-growth forest in Patagonia are formed by highly related individuals

Background and Aims Multi-stemmed trees (tree clusters) in Nothofagus pumilio, a dominant tree species in Patagonia, are very uncommon and are restricted to the edge of second-growth forests following human-provoked fires. No vegetative reproduction has been reported so far. The genetic structure of multi-stemmed trees of this species was investigated and it was hypothesized that genets within a cluster were more closely related than average in the population. Methods Fifteen clusters (composed of at least three purported stems) and 15 single trees were sampled at the edge of a second-growth forest and genotyped using two amplified fragment length polymorphism (AFLP) primer pairs. We obtained 119 polymorphic markers that allowed clonality to be determined, together with sibship structure and relatedness among samples. Key Results Clonality was detected in seven clusters but all clusters had at least two different genotypes. Full sibs were found exclusively within clusters and in all clusters. Within a cluster, stems that were not identified as full sibs were often half sibs. Relatedness values for the full sibs and half sibs were higher than the theoretical values of 0·5 and 0·25 but the relatedness between clusters was very low. Conclusions Tree clusters that are merged at the edge of the second-growth forest of N. pumilio are composed of stems of the same genotype and of other genotypes that are highly related (but not always). It is suggested that this peculiar genetic structure results from a combination of several causes, including selection for merging of related individuals.