Vulnerability to cavitation of leaf minor veins: any impact on leaf gas exchange?

Vulnerability to cavitation of leaf minor veins and stems of Laurus nobilis L. was quantified together with that of leaflets, rachides and stems of Ceratonia siliqua L. during air‐dehydration of 3‐year‐old branches. Embolism was estimated by counting ultrasound acoustic emissions (UAE) and relating them to leaf water potential (Ψ_L). The threshold Ψ_L for cavitation was less negative in L. nobilis than in C. siliqua according to the known higher drought resistance of the latter species. Leaf minor vein cavitation was also quantified by infiltrating leaves with fluorescein at different dehydration levels and observing them under microscope. Distinct decreases in the functional integrity of minor veins were observed during leaf dehydration, with high correlation between the two variables. The relationship between leaf conductance to water vapour (g_L) and Ψ_L showed that stomata of L. nobilis closed in response to stem and not to leaf cavitation. However, in C. siliqua, g_L decreased in coincidence to the leaf cavitation threshold, which was, nevertheless, very close to that of the stem. The hypothesis that stem cavitation acts as a signal for stomatal closure was confirmed, while the same role for leaf cavitation remains an open problem.     

Anomalies of the forebrain with radial limb defects: Garcia‐Lurie‐Steinfeld syndrome?

BACKGROUND: Severe anomalies of the forebrain together with radial limb anomalies have been reported in Steinfeld syndrome, XK aprosencephaly, and partial monosomy 13q. Steinfeld syndrome is an extremely variable autosomal dominant condition that, in severe cases, is characterized by holoprosencephaly, radial limb defects, and renal and/or cardiac defects. In mild cases there may be only thumb hypoplasia, ocular coloboma, or oral clefts. XK aprosencephaly, also called Garcia-Lurie syndrome (GLS), is a usually sporadic disorder with radial limb defects and aprosencephaly/atelencephaly. Based on two atypical sibships, autosomal recessive inheritance has been suggested. Two patients with variations of monosomy 13q have been described with atelencephaly but, generally, Steinfeld and XK aprosencephaly patients are chromosomally normal. Holoprosencephaly in 13q deletion patients appears to be due to ZIC2 mutations, but ZIC2 has not been previously tested in Steinfeld syndrome or GLS patients. CASES: We report three sporadic cases with clinical features intermediate between Steinfeld and GLS, including severe forebrain malformations and radial limb defects. All had normal karyotypes, and mutations in ZIC2 were absent in the two cases tested. CONCLUSIONS: In our cases and in the literature there is significant clinical overlap between Steinfeld syndrome and GLS. We propose these conditions may not be nosologically or etiologically distinct. The spectrum of severe forebrain anomalies in these conditions is broader than previously thought and may include some neural tube defects. Mild cases are difficult to identify and the full range of expression remains unknown. Autosomal dominant inheritance with incomplete penetrance and frequent new mutations is postulated. Thorough clinical evaluation is recommended for children with severe forebrain and radial limb defects.     

Arbuscular mycorrhiza increased the activity of a biotrophic leaf pathogen – is a compensation possible?

Arbuscular mycorrhizal barley-plants were more susceptible to the obligate biotrophic shoot pathogen Erysiphe graminis f. sp. hordei. In experiments under greenhouse and open-air conditions on leaves of mycorrhizal plants, the sporulation rate of the mildew fungus was more than twice that on control plants. However, mycorrhizal plants suffered less than non-mycorrhizal plants in terms of grain number, ear yield and thousand-grain weight. Disease-yield-relationship analysis showed that the symbiosis neutralised the positive correlation between disease severity and yield loss (up to 25% infected leaf area tested). After mildew infection, nitrogen in ears of non-mycorrhizal barley was higher because of an impaired starch accumulation during grain filling. In mycorrhizal plants, leaf disease did not impair either the quantity or quality of grain yield. This improved compensation in mycorrhizal plants was related to maintained photosynthetic capacity and a delay in pathogen-induced senescence. Thus filling of long-term storage pools (fructans in internodes) and consequently reallocation of these reserves during grain filling was improved. The results suggest that higher availability of energy and material during grain formation, together with longer physiological activity, were the basis of yield maintenance and, therefore, expression of mycorrhiza-induced tolerance towards the pathogen.     

Stream hydraulics and the distribution of microcrustacea: a role for refugia?

1. The relationship between microcrustacean abundance and flow habitat in three contrasting reaches of a single stream was examined. 2. Three methods of characterizing stream hydraulics (shear stress frequency distributions, Froude numbers and mean reach velocity) showed the same pattern among the three reaches, which were subsequently termed ‘fast’, ‘slow’ and ‘medium’. 3. Distributions of epibenthic microcrustacea matched flow characteristics of the three reaches, being most abundant in the slow reach and least abundant in the fast reach. In contrast, densities of three out of four species of interstitial Harpacticoida did not vary significantly with reach, and none of the parameters measured explained much of their between-patch variation in density. Hydraulic conditions at the substratum surface may not affect the distribution of species with interstitial habits. 4. Patterns in the abundance of organic matter (a possible food source) were examined. Measures of organic matter were highly correlated with hydraulic variables, with detritus being most abundant in the slow reach and least in the fast reach. Despite their strong response to reach, local densities of most microcrustacea (including many epibenthic species) did not vary with organic matter. Food for detritivorous microcrustacea may not be limiting in this highly retentive stream. 5. There was some evidence to suggest that different numbers of animals were retained in the three reaches during flow disturbances. One reach may function as a ‘flow refugium’. Models illustrating the processes by which lotic organisms may use flow refugia are presented and provide a framework for future empirical and theoretical studies.     

Cold‐water coral habitats on seamounts: do they have a specialist fauna?

Aim The large biogenic structures formed by colonial cold‐water scleractinian corals provide valuable habitat for marine invertebrates on seamounts and the continental slope of all world oceans. These patchily distributed long‐lived structures are easily damaged by several human activities, particularly bottom trawling for fish, and are potentially vulnerable to ocean acidification caused by climate change. Consequently, an important conservation question is whether these structures support a specialized invertebrate fauna restricted to these habitats. Here we investigate the relationship between structures formed by the coral Solenosmilia variabilis and its associated ophiuroid (brittlestar) fauna, one of the dominant components of deep‐sea ecosystems. Location Seafloor habitat around Southern Australia, New Zealand, and the Macquarie Ridge from 35 to 53° S and 117° E–176° W, 500–1500 m depth. Methods Data were derived from samples collected by numerous scientific expeditions to the study region. Because these samples were collected using a variety of gear and effort, a two‐step approach was used. First, the largest consistently collected data set (73 ophiuroid species from 59 samples) was assembled for multivariate analysis. ANOSIM was used to test for differences in ophiuroid community composition between Solenosmilia and non‐Solenosmilia habitat on seamounts and the continental slope, and SIMPER was used to identify species that characterized Solenosmilia habitat. Second, these results were validated against all known data to ensure that these characteristic species had not been found in non‐Solenosmilia habitat elsewhere. Results The ophiuroid assemblages from Solenosmilia habitat were distinct from those found on other habitats on the continental slope and offshore seamounts across the study region. Although a suite of ophiuroid species characterized Solenosmilia habitat, most have also been collected from dead coral or other rubble, suggesting a physical rather than biological association between the coral matrix and its associated invertebrate fauna. Main conclusions Despite the lack of an exclusive ophiuroid–coral relationship, cold‐water scleractinian coral remains the principal habitat for a number of ophiuroid species across southern Australia and New Zealand. The slow growth rate of the coral and the low dispersal potential of some associated species suggest that recovery of damaged cold‐water coral assemblages will be a long‐term process.     

Smoke on the water: Can riverine fish populations recover following a catastrophic fire‐related sediment slug?

Abstract In early 2003 a series of large, wildfire‐related sediment slugs occurred in streams in the south‐eastern Australian alpine region. Back‐pack and boat‐mounted electrofishing were used to measure changes in riverine fish fauna after one particularly large sediment slug which started in an upland stream and then travelled downstream through 200 km of third and fourth order stream. Twelve impact sites and eight control sites were surveyed where there were previous data on fish populations. The sites were surveyed directly after the sediment slug had passed and then 12, 24 and 36 months after. Immediately after the sediment slug, fish abundances fell by between 95–100% at four impact sites in the upper reaches of the study area, primarily due to the effect of low‐dissolved oxygen levels. Twelve months later fish numbers were still decreased in the upper catchment but showed signs of recovery after 24 months. Further downstream, where water quality was not as severely affected by the sediment slug, the effects on native fishes were less apparent. The circumstances of these events represented a unique opportunity to obtain baseline data regarding the effects of post‐fire disturbances on fish, and their time to recovery. If fire were to occur in catchments where endangered species exist, our results suggest that actions such as translocation may be required to ensure the long‐term survival of threatened species.     

The impact of effluents of Pitkäranta pulp mill on the water quality of Lake Ladoga: a model study

The aim of this study is to show the effects of the Pitkäranta pulp mill on the water quality of Northern Ladoga by using water quality models. The effluent loading of the pulp mill with its full production capacity is as follows: Water flow 85 000 m³ d^–1 BOD₅ 2.4 t d^–1 Suspended solids 4.1 t d^–1 tot-N 330 kg d^–1 tot-P 68 kg d^–1 COD(Cr) 14.4 t d^–1 Org. C 6 t d^–1 Lignosulphonates 9.4 t d^–1 Loadings of lignosulphonates and organic C are estimations. Lignosulphonate concentrations of 10.5 mg 1^–1 have been reported in the region of Pitkäranta. The study area of northern Ladoga near the pulp mill was divided into three zones (I, II and III). The mean depth of each of them is considered as 10 m, their respective areas 5, 10 and 50 km², and volumes 50, 100 and 500 million m³. The estimated discharges of the zones are 10, 20 and 50 m³ s^–1, respectively. With the aid of simple water quality models the effects of the pulp mill effluents on the concentrations of oxygen, total phosphorus, lignin, COD(Mn) and Secchi disk depths in each of the zones were estimated. Estimations were made during full production capacity and half production capacity of the pulp mill. The modelling results were compared with the preliminary water analysis results of the Finnish-Russian joint research expedition into Lake Ladoga in August 1993. The results show that near the pulp mill (zone I) phosphorus concentrations are high even with half production capacity. Also lignin and COD(Mn) contents have increased, and oxygen concentrations are low both in the summer and during wintertime. Farther away in the open water (zone III) the pollution effects are low. Eutrophication, indicated by high total phosphorus concentrations, is the main effect of the pulp mill effluents.     

5‐Hydroxymethylcytosine: a new kid on the epigenetic block?

The discovery of the Ten‐Eleven‐Translocation (TET) oxygenases that catalyze the hydroxylation of 5‐methylcytosine (5mC) to 5‐hydroxymethylcytosine (5hmC) has triggered an avalanche of studies aiming to resolve the role of 5hmC in gene regulation if any. Hitherto, TET1 is reported to bind to CpG‐island (CGI) and bivalent promoters in mouse embryonic stem cells, whereas binding at DNAseI hypersensitive sites (HS) had escaped previous analysis. Significant enrichment/accumulation of 5hmC but not 5mC can indeed be detected at bivalent promoters and at DNaseI‐HS. Surprisingly, however, 5hmC is not detected or present at very low levels at CGI promoters notwithstanding the presence of TET1. Our meta‐analysis of DNA methylation profiling points to potential issues with regard to the various methodologies that are part of the toolbox used to detect 5mC and 5hmC. Discrepancies between published studies and technical limitations prevent an unambiguous assignment of 5hmC as a ‘true’ epigenetic mark, that is, read and interpreted by other factors and/or as a transiently accumulating intermediary product of the conversion of 5mC to unmodified cytosines.     

5‐HTTLPR S‐allele: a genetic plasticity factor regarding the effects of life events on personality?

The S-allele of the 5-HTTLPR has been identified as a genetic vulnerability factor, being associated with an increased risk for affective disorders and/or maladaptive traits (e.g. neuroticism), especially after exposition to negative life-events (LEs). Alternatively, it has been hypothesized that this genetic risk factor might constitute a genetic plasticity factor. That is, S-allele carriers are not only vulnerable to the negative effects of a preponderance of stressful LEs but also disproportionally benefit from a preponderance of positive environmental influences. We tested this hypothesis in 357 subjects who were genotyped for the 5-HTTLPR and provided self-reports of neuroticism, life-satisfaction and LEs. Results showed a relatively increased number of positive LEss to be associated with reduced neuroticism (men: β = -0.501, P < 0.05, women: β = -0.369, P < 0.005) and increased life satisfaction (β = 0.494, P < 0.001) within SS-homozygotes. Within SL-heterozygotes, similar tendencies were found. No associations were detected in LL-homozygotes. Extreme Group comparisons revealed a genotype × LE interaction (F(2,198) = 5.593, P < 0.005), with SS-homozygotes having experienced predominantly positive LEs exhibiting reduced neuroticism (women: F(1,34) = 4.764, P < 0.05; men: F(1,17) = 2.092, P = 0.17), and increased life satisfaction (F(1,53) = 4.057, P < 0.05), as compared to LL-homozygotes having experienced predominantly positive LEs. Our data support the idea that the S-allele of the 5-HTTLPR is associated with an overall increased reactivity to environmental influences, be they positive or negative in nature. These findings constitute a promising add-on to earlier data and support the plasticity hypothesis.     

Levels of polymorphism on the sex‐limited chromosome: a clue to Y from W?

Nucleotide diversity of the human Y chromosome is much lower than that in the rest of the genome. A new hypothesis postulates that this invariance may result from mutations in maternally inherited mitochondrial DNA (mtDNA), leading to impaired reproduction among males and lowered male effective population size. If correct, we should expect to see low levels of polymorphism in the male-specific Y chromosome of many organisms but not necessarily in the female-specific W chromosome in organisms with female heterogamety. However, recent observations from birds suggest that the avian W chromosome is very low in nucleotide diversity. This indicates that mtDNA mutations cannot broadly explain the evolution of the sex-limited chromosome. Other work has suggested that sexual selection at loci involved in sex determination or secondary sexual characteristics might reduce levels of genetic variability on Y through hitch-hiking effects. Although the W chromosome does not seen to play a dominant role for sex determination in birds, it cannot be excluded that selective sweeps arising from natural or sexual selection contribute to the low levels of genetic variability seen on this chromosome.     

Bundle‐sheath cell regulation of xylem‐mesophyll water transport via aquaporins under drought stress: a target of xylem‐borne ABA?

The hydraulic conductivity of the leaf vascular system (K_leaf) is dynamic and decreases rapidly under drought stress, possibly in response to the stress phytohormone ABA, which increases sharply in the xylem sap (ABA_xyl) during periods of drought. Vascular bundle‐sheath cells (BSCs; a layer of parenchymatous cells tightly enwrapping the entire leaf vasculature) have been hypothesized to control K_leaf via the specific activity of BSC aquaporins (AQPs). We examined this hypothesis and provide evidence for drought‐induced ABA_xyl diminishing BSC osmotic water permeability (P_f) via downregulated activity of their AQPs. ABA fed to the leaf via the xylem (petiole) both decreased K_leaf and led to stomatal closure, replicating the effect of drought. In contrast, smearing ABA on the leaf blade, while also closing stomata, did not decrease K_leaf within 2–3 h of application, demonstrating that K_leaf does not depend entirely on stomatal closure. GFP‐labeled BSCs showed decreased P_f in response to ‘drought’ and ABA treatment, and a reversible decrease with HgCl₂ (an AQP blocker). These P_f responses, absent in mesophyll cells, suggest stress‐regulated AQP activity specific to BSCs, and imply a role for these cells in decreasing K_leaf via a reduction in P_f. Our results support the above hypothesis and highlight the BSCs as hitherto overlooked vasculature sensor compartments, extending throughout the leaf and functioning as ‘stress‐regulated valves’ converting vasculature chemical signals (possibly ABA_xyl) into leaf hydraulic signals.     

Biometry of Cenomanian–Turonian placoliths: a proxy for changes of fertility and surface‐water temperature?

Most publications discussing Cenomanian–Turonian calcareous nannofossils focus on abundance fluctuations across the boundary interval. So far, there have been no studies that deal with the influence of palaeoenvironmental changes on the size of common Cenomanian–Turonian nannofossil taxa. The genera Biscutum, Broinsonia, Prediscosphaera, Retecapsa and Watznaueria have therefore been analysed from 19 samples of Cenomanian–Turonian age from the Goban Spur, northeast Atlantic. The genus Biscutum shows a slight decrease of mean length from 4.14 μm in the Cenomanian to 3.94 μm in the Turonian. Broinsonia is marked by a decrease from 6.07 μm in the Cenomanian to 5.64 μm in the Turonian. On the other hand, Prediscospheara increases in size from 4.98 μm in the Cenomanian to 5.61 μm in the Turonian. Two genera (Retecapsa, Watznaueria) show no significant changes in their mean length. The mean size of Biscutum is perhaps controlled by nutrients, where larger specimens may have preferred the more fertile palaeoenvironment of the Late Cenomanian. The size decrease of Biscutum in the Turonian is probably related to reduced nutrient availability. The genus Prediscosphaera spp., may have favoured low‐fertility conditions, as its mean size increases in the Turonian. A worldwide decline of the frequency of Broinsonia spp. during the Cenomanian–Turonian transition implies that this genus is not solely controlled by the nutrient content. The size of Broinsonia spp. may have been therefore influenced by the latest Cenomanian warming event. The increase in sea‐surface temperature may have been unfavourable for Broinsonia spp. as reflected by decreasing mean size and frequency. □Calcareous nannofossils, biometry, morphometry, Oceanic Anoxic Event 2.     

Major diffusion leaks of clamp‐on leaf cuvettes still unaccounted: how erroneous are the estimates of Farquhar et al. model parameters?

Estimates of leaf gas-exchange characteristics using standard clamp-on leaf chambers are prone to errors because of diffusion leaks. While some consideration has been given to CO(2) diffusion leaks, potential water vapour diffusion leaks through chamber gaskets have been neglected. We estimated diffusion leaks of two clamp-on Li-Cor LI-6400 (Li-Cor, Inc., Lincoln, NE, USA) leaf chambers with polymer foam gaskets and enclosing either 2 or 6 cm(2) leaf area, and conducted a sensitivity analysis of the diffusion leak effects on Farquhar et al. photosynthesis model parameters - the maximum carboxylase activity of ribulose 1 x 5-bisphosphate carboxylase/oxygenase (Rubisco) (V(cmax)), capacity for photosynthetic electron transport (J(max)) and non-photorespiratory respiration rate in light (R(d)). In addition, net assimilation rate (A(n)) versus intercellular CO(2) (C(i)) responses were measured in leaves of Mediterranean evergreen species Quercus ilex L. enclosing the whole leaf chamber in a polyvinyl fluoride bag flushed with the exhaust air of leaf chamber, thereby effectively reducing the CO(2) and water vapour gradients between ambient air and leaf chamber. For the empty chambers, average diffusion leak for CO(2), K(CO2), (molar flow rate corresponding to unit CO(2) mole fraction difference) was ca. 0.40 micromol s(-1). K(CO2) increased ca. 50% if a dead leaf was clamped between the leaf chamber. Average diffusion leak for H(2)O was ca. 5- to 10-fold larger than the diffusion leak for CO(2). Sensitivity analyses demonstrated that the consequence of a CO(2) diffusion leak was apparent enhancement of A(n) at high CO(2) mole fraction and reduction at lower CO(2) mole fraction, and overall compression of C(i) range. As the result of these modifications, Farquhar et al. model parameters were overestimated. The degree of overestimation increased in the order of V(cmax) < J(max) < R(d), and was larger for smaller chambers and for leaves with lower photosynthetic capacity, leading to overestimation of all three parameters by 70-290% for 2 cm(2), and by 10-60% for 6 cm(2) chamber. Significant diffusion corrections (5-36%) were even required for leaves with high photosynthetic capacity measured in largest chamber. Water vapour diffusion leaks further enhanced the overestimation of model parameters. For small chambers and low photosynthetic capacities, apparent C(i) was simulated to decrease with increasing A(n) because of simultaneous CO(2) and H(2)O diffusion leaks. Measurements in low photosynthetic capacity Quercus ilex leaves enclosed in 2 cm(2) leaf chamber exhibited negative apparent C(i) values at highest A(n). For the same leaves measured with the entire leaf chamber enclosed in the polyvinyl fluoride bag, C(i) and A(n) increased monotonically. While the measurements without the bag could be corrected for diffusion leaks, the required correction in A(n) and transpiration rates was 100-500%, and there was large uncertainty in Farquhar et al. model parameters derived from 'corrected'A(n)/C(i) response curves because of uncertainties in true diffusion leaks. These data demonstrate that both CO(2) and water vapour diffusion leaks need consideration in measurements with clamp-on leaf cuvettes. As plants in natural environments are often characterized by low photosynthetic capacities, cuvette designs need to be improved for reliable measurements in such species.     

Do hormone‐modulating chemicals impact on reproduction and development of wild amphibians?

Globally, amphibians are undergoing a precipitous decline. At the last estimate in 2004, 32% of the approximately 6000 species were threatened with extinction and 43% were experiencing significant declines. These declines have been linked with a wide range of environmental pressures from habitat loss to climate change, disease and pollution. This review evaluates the evidence that endocrine‐disrupting contaminants (EDCs) – pollutants that affect hormone systems – are impacting on wild amphibians and contributing to population declines. The review is limited to anurans (frogs and toads) as data for effects of EDCs on wild urodeles (salamanders, newts) or caecilians (limbless amphibians) are extremely limited. Evidence from laboratory studies has shown that a wide range of chemicals have the ability to alter hormone systems and affect reproductive development and function in anurans, but for the most part only at concentrations exceeding those normally found in natural environments. Exceptions can be found for exposures to the herbicide atrazine and polychlorinated biphenyls in leopard frogs (Rana pipiens) and perchlorate in African clawed frogs (Xenopus laevis). These contaminants induce feminising effects on the male gonads (including ‘intersex’ – oocytes within testes) at concentrations measured in some aquatic environments. The most extensive data for effects of an EDC in wild amphibian populations are for feminising effects of atrazine on male gonad development in regions across the USA. Even where strong evidence has been provided for feminising effects of EDCs, however, the possible impact of these effects on fertility and breeding outcome has not been established, making inference for effects on populations difficult. Laboratory studies have shown that various chemicals, including perchlorate, polychlorinated biphenyls and bromodiphenylethers, also act as endocrine disrupters through interfering with thyroid‐dependent processes that are fundamental for amphibian metamorphosis. Perchlorate has also been shown to induce these effects in wild anuran populations from perchlorate‐contaminated environments. Overall, the published data available suggest that some health effects observed in wild anuran populations, most notably intersex, likely have a chemical aetiology; however they derive only from very few anuran species and for a few pesticides at field sites in the USA. To understand better the impacts of EDCs on wild anuran populations, as well as other amphibian groups, assessment of fertility in exposed animals are required. Development of non‐destructive biomarkers that are indicative of specific EDC‐effect mechanisms are also needed to allow the study of vulnerable populations. This will help to distinguish the effects of EDCs from other environmental and/or genetic influences on development and reproduction.     

Anti-IgE autoantibodies: a possible specific feedback on the cytokine network in allergy?

We propose a theoretical model based on the cytokine network, that provides the necessary signals so that basically all human beings can produce IgE but not all have to develop allergic disease. Our hypothesis implies that anti-IgE autoantibodies are a kind of emergency brake neutralizing the IgE induced by the cytokine network. In the normal individual the system would come to halt at this point. However, the atopic individual, due to a small difference in his or her B cell repertoire, will produce the wrong type of anti-IgE antibody. Allergic disease can now develop because IgE is not perfectly neutralized. The wrong type of anti-IgE antibody that is now produced may even aggravate the disease as some of these autoantibodies may induce IgE synthesis or trigger effector cells that in turn generate a Th2 like cytokine pattern closing the vicious circle. We believe that because of the potency of the powerful and archaic cytokine network, we have to dispose of such a specific control mechanism by autoantibodies.