A new role for glutathione in the regulation of root architecture linked to strigolactones

Reduced glutathione (GSH) is required for root development, but its functions are not characterized. The effects of GSH depletion on root development were therefore studied in relation to auxin and strigolactone (SL) signalling using a combination of molecular genetic approaches and pharmacological techniques. Lateral root (LR) density was significantly decreased in GSH synthesis mutants (cad2‐1, pad2‐, rax1‐), but not by the GSH synthesis inhibitor, buthionine sulfoximine (BSO). BSO‐induced GSH depletion therefore did not influence root architecture in the same way as genetic impairment. Root glutathione contents were similar in the wild‐type seedlings and max3‐9 and max4‐1 mutants that are deficient in SL synthesis and in the SL‐signalling mutant, max2‐1. BSO‐dependent inhibition of GSH synthesis depleted the tissue GSH pool to a similar extent in the wild‐type and SL synthesis mutants, with no effect on LR density. The application of the SL analogue GR24 increased root glutathione in the wild‐type, max3‐9 and max4‐1 seedlings, but this increase was absent from max2‐1. Taken together, these data establish a link between SLs and the GSH pool that occurs in a MAX2‐dependent manner.     

Relative Nitrogen Limitation at Steady-state Nutrition as a Determinant of Plasticity in Five Grassland Plant Species

Partitioning of biomass between roots and different shoot partshas often been used to explain the response of plants to variationsin resource availability. There are still many uncertaintiesin the importance of this trait for plant performance, and clearguidelines on how partitioning should be quantified in relationto growth rate and resource supply are of fundamental importancefor such an understanding. This paper reports an attempt toshow how plant nitrogen status relates to root:shoot partitioningand other plastic responses, in a manner that can be used forquantitative predictions. The reactions to nitrogen limitationof five grassland plant species, with different ecological demands,were compared. The species used were the forbs Polygala vulgarisand Crepis praemorsa, and the grasses Danthonia decumbens, Agrostiscapillaris and Dactylis glomerata. The experiment was conductedin a climate chamber where the plants were grown hydroponically(1) under non-limiting nutrient conditions and (2) at a steady-statenitrogen limitation, which enabled the plants to express halfof their growth potential. The relative growth rate (RGR) ofthe species was strongly related to plant nitrogen concentration(PNC) and leaf area ratio (LAR), whereas the effects on netassimilation rate (NAR) were very small. Despite large differencesin maximum relative growth rate, the species showed remarkablesimilarities in dry matter partitioning between root and shoot.It is concluded that root:shoot partitioning can be treatedas a direct function of the relative resource limitation ofthe plant. The difficulty of attaining well-defined levels ofresource limitation in soil, other solid substrates and manyhydroponic systems may be the most important reason for thedivergent results in earlier studies. Better knowledge of soil-rootinteractions, and plant responses to the whole span of resource-supplylevels, is required for a thorough understanding of how nutrientslimit growth. Copyright 1999 Annals of Botany Company Growth rate, plant strategies, plasticity, partitioning, biomass, nitrogen, nutrient limitation, grassland.     

Gerometabolites: The pseudohypoxic aging side of cancer oncometabolites

Oncometabolites are defined as small-molecule components (or enantiomers) of normal metabolism whose accumulation causes signaling dysregulation to establish a milieu that initiates carcinogenesis. In a similar manner, we propose the term “gerometabolites” to refer to small-molecule components of normal metabolism whose depletion causes signaling dysregulation to establish a milieu that drives aging. In an investigation of the pathogenic activities of the currently recognized oncometabolites R(-)-2-hydroxyglutarate (2-HG), fumarate, and succinate, which accumulate due to mutations in isocitrate dehydrogenases (IDH), fumarate hydratase (FH), and succinate dehydrogenase (SDH), respectively, we illustrate the fact that metabolic pseudohypoxia, the accumulation of hypoxia-inducible factor (HIFα) under normoxic conditions, and the subsequent Warburg-like reprogramming that shifts glucose metabolism from the oxidative pathway to aerobic glycolysis are the same mechanisms through which the decline of the “gerometabolite” nicotinamide adenine dinucleotide (NAD)⁺ reversibly disrupts nuclear–mitochondrial communication and contributes to the decline in mitochondrial function with age. From an evolutionary perspective, it is reasonable to view NAD⁺-driven mitochondrial homeostasis as a conserved response to changes in energy supplies and oxygen levels. Similarly, the natural ability of 2-HG to significantly alter epigenetics might reflect an evolutionarily ancient role of certain metabolites to signal for elevated glutamine/glutamate metabolism and/or oxygen deficiency. However, when chronically altered, these responses become conserved causes of aging and cancer. Because HIFα-driven pseudohypoxia might drive the overproduction of 2-HG, the intriguing possibility exists that the decline of gerometabolites such as NAD⁺ could promote the chronic accumulation of oncometabolites in normal cells during aging. If the sole activation of a Warburg-like metabolic reprogramming in normal tissues might be able to significantly increase the endogenous production of bona fide etiological determinants in cancer, such as oncometabolites, this undesirable trade-off between mitochondrial dysfunction and activation of oncometabolites production might then pave the way for the epigenetic initiation of carcinogenesis in a strictly metabolic-dependent manner. Perhaps it is time to definitely adopt the view that aging and aging diseases including cancer are governed by a pivotal regulatory role of metabolic reprogramming in cell fate decisions.     

Influence of simulated climate change and eutrophication on three‐spined stickleback populations: a large scale mesocosm experiment

1. Shallow lakes and their ectothermic inhabitants are particularly vulnerable to the effects of climatic warming. These impacts are likely to depend on nutrient loading, especially if the combination of warming and eutrophication leads to severe hypoxia. 2. To investigate effects of realistic warming and nutrient loading on a fish species with high tolerance of warming and hypoxia, we observed population changes and timing of reproduction of three‐spined sticklebacks in 24 outdoor shallow freshwater ecosystems with combinations of temperature (ambient and ambient +4 °C) and three nutrient treatments over 16 months. 3. Warming reduced stickleback population biomass by 60% (population size by 76%) and nutrient‐addition reduced biomass by about 80% (population size 95%). Nutrients and warming together resulted in extinction of the stickleback populations. These losses were mainly attributed to the increased likelihood of severe hypoxia in heated and nutrient‐addition mesocosms. 4. Warming of nutrient‐rich waters can thus have dire consequences for freshwater ectotherm populations. The loss even of a hardy fish suggests a precarious future for many less tolerant species in such eutrophic systems under current climate change predictions.     

Sex combs,allometry, and asymmetry in Drosophila

There has been recent debate about the expected allometry of sexually‐selected traits. Although sexually‐selected traits exhibit a diversity of allometric patterns, signalling characters are frequently positively allometric. By contrast, insect genitalia tend to be negatively allometric, although the allometry of nongenital sexually‐selected characters in insects is largely unknown (with some notable exceptions). It has also been suggested that there should be a negative association between the asymmetry and size of bilaterally‐paired, sexually‐selected traits, although this claim is controversial. We assessed the allometry and asymmetry (fluctuating asymmetry, FA) of a nongenital contact–courtship structure, the sex comb, in replicate populations of three species of Drosophila (we also measured wing FA). Sex combs are sexually‐selected characters used to grasp the female's abdomen and genitalia and to spread her wings prior to and during copulation. Although species differed in the size of the sex combs, all combs were positively allometric, and comb allometry did not generally differ significantly between species or populations. Comb and wing asymmetry did vary across species, although not across populations of the same species. However, FA was trait specific and was never negatively associated with trait size. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 923–934.     

A select panel of polymorphic microsatellite loci for individual identification of snow leopards (Panthera uncia)

Snow leopards (Panthera uncia) are elusive endangered carnivores found in remote mountain regions of Central Asia. New methods for identifying and counting snow leopards are needed for conservation and management efforts. To develop molecular genetic tools for individual identification of hair and faecal samples, we screened 50 microsatellite loci developed for the domestic cat (Felis catus) in 19 captive snow leopards. Forty‐eight loci were polymorphic with numbers of alleles per locus ranging from two to 11. The probability of observing matching genotypes for unrelated individuals (2.1 × 10^?11) and siblings (7.5 × 10^?5) using the 10 most polymorphic loci was low, suggesting that this panel would easily discriminate among individuals in the wild.     

Detectability of American Mink Using Rafts to Solicit Field Signs in a Population Control Context

Abstract: American mink (Neovison vison) are an ecologically damaging invasive species where they have been introduced in Europe. Effectiveness of mink population control by trapping has been difficult to assess, without knowing how efficiently mink are caught by traps or detected by other methods. Use of track-recording rafts to detect mink and guide trapping effort has proved efficient and leads to a supposition that no detection indicates absence of mink. To draw this conclusion with any confidence requires a measure of detectability. We applied occupancy models to data from an earlier study to estimate detectability of individual American mink on track-recording rafts. Estimated detectability of individual mink, per raft, and 2-week check period varied between 0.4 in late summer and 0.6 in late autumn. By inference, risk of failing to detect a mink that was present would be <5% given 4–6 independent opportunities to detect it. These opportunities could be created either by using a raft spacing that ensured multiple detections of each mink or by monitoring rafts through a succession of check intervals. Within certain simple constraints, raft location did not contribute substantially to detection probability. These findings will allow field operators, strategists, and funders to assess with confidence the success of efforts to control mink density. We expect the estimation of individual detectability to be similarly valuable in population control or eradication of other species.     

Phylogenetic diversity of Sri Lankan freshwater crabs and its implications for conservation

As part of a Global Biodiversity Hotspot, the conservation of Sri Lanka's endemic biodiversity warrants special attention. With 51 species (50 of them endemic) occurring in the island, the biodiversity of freshwater crabs is unusually high for such a small area (65 600 km²). Freshwater crabs have successfully colonized most moist habitats and all climatic and elevational zones in Sri Lanka. We assessed the biodiversity of these crabs in relation to the different elevational zones (lowland, upland and highland) based on both species richness and phylogenetic diversity. Three different lineages appear to have radiated simultaneously, each within a specific elevational zone, with little interchange thereafter. The lowland and upland zones show a higher species richness than the highland zone while – unexpectedly – phylogenetic diversity is highest in the lowland zone, illustrating the importance of considering both these measures in conservation planning. The diversity indices for the species in the various IUCN Red List categories in each of the three zones suggest that risk of extinction may be related to elevational zone. Our results also show that overall more than 50% of Sri Lanka's freshwater crab species (including several as yet undescribed ones), or approximately 72 million years of evolutionary history, are threatened with extinction.     

Sources of Inorganic Carbon Acquired through CAM in Littorella uniflora (L.) Aschers

Madsen, T. V. 1987. Sources of inorganic carbon acquired throughCAM in Littorella uniflora (L.) Aschers.—J. exp. Bot.38: 367–377. The CO₂ dynamics of the lacunal air and the relative contributionof external and internal CO₂ sources to dark CO₂ assimilationwas examined in the submerged aquatic CAM species Littorellauniflora (L.) Aschers. Refixation of internal CO₂, released by dark respiration, constitutedabout 30–35% of the total dark CO₂ assimilation. At aCO₂ concentration of 0·2 mol m^–3 around the leavesthe external CO₂ uptake through the roots increased from 45%of the total CO₂ uptake at 0·7 mol m^–3 CO₂ to 100%at 1·6 mol m^–3 and 3·1 mol m^–3 CO₂around the roots. The negligible importance of leaf CO₂ uptakeat high CO₂ concentrations around the roots was the result ofa causative high CO₂ concentration in the leaf lacunae. The CO₂ permeability of Littorella leaves was high relativeto root permeability. This has at least two ecological implications:(1) it enhances the potential diffusive release of CO₂ fromthe sediment C0₂-pool via the lacunal system of the plants.This loss of CO₂, however, was found to be greatly reduced byCAM activity of the plants. (2) The high permeability of theleaf surface to CO₂ exchange allows the plants to assimilateCO₂ from the water surrounding the leaves when the concentrationis high, i.e. during extensive epiphyte dark respiration. Thus,CAM tends to facilitate retension of a high CO₂ pool in thesediment-plant system and at the same time allows the plantsto exploit the water column CO₂ source when it is abundant.This result is in accordance with the general idea that CAMin aquatics constitute a carbon conserving mechanism. Key words: Aquatic macrophytes, dark CO₂ assimilation, inorganic carbon sources