Growth Response Curves Research Articles

Omega-3 versus Omega-6: Are We Underestimating the Ecological Significance of Arachidonic Acid in Aquatic Systems?

The long-chain polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA, ω-3, or n-3) and arachidonic acid (ARA, ω-6 or n-6) are known to have distinct physiological functions, yet can both support growth and reproduction of consumers, raising the question of whether EPA and ARA are ecologically substitutable dietary resources. We explored the relative importance of EPA and ARA for the growth and reproduction of the freshwater keystone herbivore Daphnia in a life-history experiment. Both PUFA were supplemented in a concentration-dependent manner to a PUFA-free diet, separately and in combination (50% EPA: 50% ARA mixture). The growth-response curves obtained with EPA, ARA, and the mixture were virtually congruent and the thresholds for PUFA limitation did not differ, indicating that EPA (n-3) and ARA (n-6) were substitutable dietary resources under the applied experimental conditions. The actual requirements for EPA and ARA might change with growth conditions, e.g., under the influence of parasites or pathogens. The higher retention of ARA in Daphnia suggests that EPA and ARA are subject to different turnover rates, which also implies different physiological functions. Studies on the ARA requirements of Daphnia could provide valuable information on the presumably underestimated ecological importance of ARA in freshwater food webs.

Use of calcium in bareroot pine nurseries

Bareroot nursery managers may apply dolomite, gypsum, or Ca-nitrate to increase Ca in nursery soils. Although a few managers follow S.A. Wilde’s recommendations and maintain soil at levels of 500 to 1,000 μg g-1 Ca, there is no need to keep Ca levels this high. In contrast, managers at sandy nurseries apply Ca when soil tests drop below 200 μg g-1 Ca. In fact, acceptable pine seedlings have been produced in irrigated soil with <100 μg g-1 available Ca. In plantations, asymptomatic wildlings grow when topsoil contains 17 μg g-1 Ca. In sandy soils, applying too much gypsum can result in a temporary Mg deficiency and too much lime will result in chlorotic needles.
 Managers apply Ca when foliar levels fall below a published “critical value.” The belief that the critical value for Ca varies by stock type is not valid. In fact, numerous “critical” values are invalid since they were not determined using growth response curves. Critical values determined for small seedlings using CaCl2 in sand are apparently not valid for use in bareroot nurseries. 
 At bareroot nurseries, the soil extractable Ca level can decline during a year by 30 μg g-1 or more. Harvesting 1.7 million pine seedlings may remove 20 kg ha-1 of Ca but irrigation can replace this amount or more. When water contains 5 mg l-1 Ca, 600 mm of irrigation will add 30 kg ha-1 Ca. In some areas, 1,000 mm of rainfall will supply 7 kg ha-1 Ca. Even when a Mehlich 1 test shows no exchangeable Ca in the topsoil, pine needles on tall trees may exceed 2,000 μg g-1 Ca due to root growth in subsoil.
 There are few documented cases of deficient pine needles (<300 μg g-1 Ca) in irrigated nurseries in Australia, New Zealand, Scotland and in the Americas. Even when soil fumigation delays the inoculation of ectomycorrhiza, bareroot pines have adequate levels of Ca. Typically, foliage samples from pine nurseries contain at least 1,000 μg g-1 Ca. Samples from 9-month-old seedlings range from 300 to 11,000 μg g-1 Ca. Although the “critical value” for Pinus echinata foliage is not known, 1-0 seedlings with 300 μg g-1 Ca were not stunted and apparently grew well after ouplanting.

Antibiotics Sensitivity of Escherichia coli to Different Concentrations of Combined Herbal Drugs

Background: The use of combinational approach in chemotherapeutic management has proven more effective against infectious disease and lower resistance development but the untoward effect of this is yet to be explored for alternative medicine.
 Aims: This study aimed to study the effect of a combinational approach of herbal drugs on Escherichia coli response.
 Methods: E. coli was treated in different concentrations of combined herbal drugs (Beta herbal drugs and Deep root herbal mixture – BD) and (Beta herbal drug and Goko cleanser – BG). The different concentrations of the mixtures employed were: 33.3%, 11.1%, 3.7%, 1.2% and 0.4%. The bacteria concentration of 103 CFU/ml was treated in the different concentrations of the herbal drugs. The growth response of the cultures were analyzed at 24 and 48 hrs. The antibiotic sensitivity of the bacteria exposed to the herbal drugs were measured against perfloxacin (PEF), ciprofloxacin (CIP), streptomycin (S), and septrin (SEP).
 Results: The growth response curve showed growth of E. coli peaked in the lower concentrations but levelled down in the higher concentrations. 24 hr growth conditions showed much higher growth level than 48 hr. Higher concentrations of BG drug combination showed higher zones of clearance and only one concentration showed resistance: 0.4% (CIP). There was no unique pattern seen in the sensitivity of E. coli treated with BD however, there was five (5) cases of complete resistance: 0.4% (PEF), 1.2% (PEF) and 11.1% (CIP and SEP).
 Conclusion: In vitro, the combined herbal drugs do not completely eliminate E. coli. However, some concentrations of the combinations demonstrated complete resistance to the antibiotics which shows that these locally made antimicrobial could confer antibiotic resistance to E. coli.

Nutrient solutions for Arabidopsis thaliana: a study on nutrient solution composition in hydroponics systems

BackgroundThere is little information on the effect of nutrient solutions composition on Arabidopsis growth. Therefore, we compared growth performance of Arabidopsis thaliana (Col-0) grown on the most commonly used nutrient solutions in deep water culture: Hoagland and Arnon, Murashige and Skoog, Tocquin, Hermans, and Conn. In addition to these nutrient solution composition experiments, we established Arabidopsis growth response curves for nutrient solution concentration and salt stress (NaCl).ResultsArabidopsis rosette fresh and dry weight showed an approximate linear decline with NaCl dose in deep water culture, i.e. 9% reduction relative to control per unit of electrical conductivity (EC in dS m−1, for scale comprehension 1 dS m−1 equals ~ 10 mM NaCl). The Tocquin, ½Hoagland and Conn nutrient solutions had equal and optimal growth performance. Optimal nutrient solution concentration for Tocquin and Hoagland was 0.8 to 0.9 dS m−1. Close to the EC of ½Hoagland (1.1 dS m−1), which is frequently used in Arabidopsis research. Conn solution showed optimal growth at much higher EC (2 dS m−1) indicating that it is a balanced nutrient solution that matches the needs of Arabidopsis. Full Murashige and Skoog solution (5.9 dS m−1) was lethal and diluted solutions (EC of 1.6 and 1.1 dS m−1) caused stress symptoms and severe growth retardation at later developmental stages.ConclusionsArabidopsis thaliana (Col-0) plants grown in deep water culture showed a sixfold growth difference when commonly used nutrient solutions were compared. Murashige and Skoog solution should not be used as nutrient solution in deep water culture. Conn, Tocquin and ½Hoagland are balanced nutrient solutions which result in optimal Arabidopsis growth in hydroponic systems.

How does Ni fertilization affect a responsive soybean genotype? A dose study

Nickel affects a wide range of physiological processes in plants, which may result in higher growth and yield. Recent studies demonstrate that soybean genotypes show positive, but differential, responsiveness to Ni-fertilization. Thus, this study investigated the impact of supplying this micronutrient to a soybean genotype previously known to be responsive to Ni-fertilization, with the aim of identifying a suitable range of Ni for the adequate development of this crop plant. We tested, under greenhouse conditions, the effect of applying six Ni doses (0.00, 0.25, 0.50, 1.00, 3.00, and 9.00 mg kg−1) via soil to a commonly-grown soybean genotype. Soybean plants were evaluated for nutrition, physiology, growth, N-urea metabolism, and efficiency of the N2 fixation process. Nickel supply positively affected the physiology and growth of the genotype, indicating a deficiency of this micronutrient. Ni-application also led to an increased N metabolism; in particular, nodules had a higher nitrogenase activity associated with greater Ni-concentrations in areas of highest metabolic activity. By exploiting the data acquired in a growth response curve (grain yield x Ni concentration), the greatest beneficial effects were observed following an application of 3.35 mg of Ni kg−1. A supply of more than 4.25 mg of Ni kg−1 was toxic to the plants. Ni-fertilization improved the N-mineral and N-biological assimilation pathways of soybean, optimizing the overall development of the plants. Through this study, we defined a reliable and adequate Ni-range for both plants and soil, which can be used as a basis for agricultural practice. Moreover, supplying plants with Ni at the recommended doses was revealed to be safe for in natura human consumption of soybean grains; however, more studies are required to establish the appropriate safety limit standards for soybean-based food products.

In Vitro and In Vivo Characterization of a Preclinical Irradiation-Adapted Model for Ewing Sarcoma

Radiation therapy (RT) is a viable therapeutic option for Ewing sarcoma (ES) patients. However, little progress has been made to elucidate the mechanisms of radioresistance. This study establishes a novel ES irradiation-adapted model designed to assess molecular and 18F fluorodeoxyglucose (FDG) positron emission tomography (PET) alterations secondary to RT. Radiation-adapted cell lines (RACLs) were created in vitro by exposing ES human cell lines to fractionated doses of radiation. Assays to assess migration or invasion potential and RNA expression were performed on the RACLs. Orthotopic intratibial in vivo investigations were performed with irradiation-sensitive and irradiation-adapted ES cells to generate tumors. Transplanted mice were imaged using 18F-FDG PET followed by fractionated RT directed at the primary tumor. Mice were monitored for tumor regression and change in metabolic activity using 18F-FDG PET imaging. Protein expression analyses were performed on the RACLs and orthotopic tumors. Exposure to fractionated doses of radiation caused a significant increase in migratory and invasive properties in the RACLs when compared with nonirradiated wild-type ES cells. RACL transcriptomic and proteomic analysis suggests enhanced activation of the mammalian target of rapamycin-AKT pathway when compared with wild-type ES cells. Irradiation-adapted tumors demonstrated significantly less tumor regression (P=.03) than wild-type tumors. Wild-type tumors also had decreased expression of lactate dehydrogenase A protein and significantly lower metabolic activity after RT compared with irradiation-adapted tumors (P=.03). We developed novel invitro and invivo irradiation-adapted ES models. Invitro investigations revealed increased migratory and invasive phenotypes in the RACLs. Invivo investigations demonstrated increased metabolic activity and significantlydecreased sensitivity to RT in the irradiation-adapted tumors as demonstrated by growth response curves and 18F-FDG PET activity. Investigations of the RACLs identified possible radiosensitizing-dependent targets in lactate dehydrogenase A and the mammalian target of rapamycin-AKT pathway.

Apparent niche partitioning of two congeneric submerged macrophytes in small water bodies: The case of Ceratophyllum demersum L. and C. submersum L.

The congeneric submerged macrophyte species Ceratophyllum demersumL. and C. submersum L. are seldom occurring together in a water body. To investigate whether this might be due to niche partitioning, we quantified morphological characteristics and habitat conditions for Ceratophyllum demersumand C. submersum in 82 small water bodies (Western Poland). In each pond, plant material was collected in triplicate (174 samples of C. demersum and 72 of C. submersum). Maximum depth and range of physicochemical parameters were quantified inside the stands. We used RDA and GAMs to assess multivariate habitat occurrence, growth form relations and response curves. Surface area, water depth, transparency, colour of water, DIN, ammonium and nitrate were among the most important factors affecting biometric parameters of hornwort in small water bodies. GAMs modelling of the occurrence of the two species suggest that C. demersum occurs in clearer waters whereas C. submersum is found in habitats with lower light availability, due to both colour (threshold around 100mg Pt/L) and chlorophyll (threshold around 100μg/L). Further experimental studies and field studies should substantiate the ecological niche occupied by both congeners in different water bodies.

Abstract P5-08-02: Inhibition of CDK4/6 induces senescence and autophagy in ER positive breast cancers

Abstract Deregulation of the cell cycle machinery is a hallmark of breast cancer, facilitating aberrant proliferation that fuels tumorigenesis and disease progression. This makes the cell cycle, particularly the cyclin dependent kinases (CDKs) an ideal choice for drug targeting in these tumors. Palbociclib or PD0332991, a potent CDK4/6 inhibitor is a known anti-proliferative agent that induces G1 arrest and prevents tumor growth in several cancers including ER+ breast cancer. This drug has shown tremendous success in Phase II clinical trials in ER+ breast cancers and is presently undergoing phase III trials in combination with letrazole. However, little is know about its precise mechanism of action and modes of resistance in ER+ breast cancers. This is critical in understanding the biology of treatment response, drug resistance and combination strategies, and this project aims at addressing these gaps in knowledge. We have used a series of ER+ breast cancer cell lines to examine the mechanism of action of Palbociclib and identify the nodes that could mediate resistance to this agent. Our results have revealed that continuous treatment of ER+ breast cancer cells with Palbociclib results in a G1 arrest with concomitant downregulation of pRb. Treated cells undergo senescence and autophagy, but not apoptosis. Further, we have shown that the induction of quiescence or senescence and autophagy occurs in a time and dose dependent manner. Since this agent is known to be a specific CDK4/6 inhibitor, we next downregulated these kinases in our model system and subjected them to Palbociclib treatment. Interestingly, downregulation of CDK4 or CDK6 did not significantly alter the sensitivity of these cells to the anti-tumor effects of Palbociclib. Next we asked if depletion of Rb can render the cells resistant to Palbociclib. Results revealed that the complete depletion of Rb was sufficient to reduce the sensitivity of ER+ cells to Palbociclib by 4-6 fold. However, the very steep pattern of the growth response curves suggest that in the absence of Rb, Palbociclib can effectively inhibit another target, albeit, at a higher drug concentration. Lastly, to interrogate if deregulation of the G1/S checkpoint can render cells more resistant to this inhibitor, we examined if overexpression of the low molecular weight isoforms of Cyclin-E (LMW-E), which by themselves are sufficient to induce an oncogenic phenotype through constitutive phosphorylation of Rb, can mediate resistance in these cells. These results, which were similar to those from the Rb knockout studies, revealed that LMW-E overexpression can reduce the sensitivity of ER+ breast cancer cells to Palbociclib by 5-7 fold. Collectively, our studies suggest that inhibition of G1/S transition is not the sole mode of action of Palbociclib and that there is another unidentified target, which is specifically inhibited by this agent, when the G1/S check point is compromised. Since the deregulation of the G1/S checkpoint is likely to occur clinically in patients treated with Palbociclib, identification of this second target will be instrumental in efforts to overcome resistance and identify biomarkers of sensitivity to this agent in breast cancer patients. Citation Format: Smruthi Vijayaraghavan, Khandan Keyomarsi. Inhibition of CDK4/6 induces senescence and autophagy in ER positive breast cancers [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-08-02.

Reference Curve for the First-Year Growth Response to Growth Hormone Treatment in Prepubertal Children with Idiopathic Growth Hormone Deficiency: Validation of the KIGS First-Year Growth Response Curve Using the Belgian Register for the Study of Growth and Puberty Problems

Background: Comparing observed and expected growth after first-year growth hormone (GH) therapy is useful for identifying a poor growth response to GH. Aim: To generate a first-year, age-specific growth response reference curve for prepubertal Belgian children with idiopathic growth hormone deficiency (iGHD) treated with a standard weight-adjusted GH dose and to compare this national reference with the response references derived from KIGS. Subjects and Methods: First-year height data of 357 prepubertal children (240 males) with iGHD were analyzed. Smooth reference curves of first-year height velocity (HV) in relation to age were created. Differences with the KIGS targets were evaluated after z-score transformation. Results: The observed first-year HVs were log-normal distributed by age and decreased significantly with age (p < 0.001). No GH dose or gender effect was observed (p = 0.5). Distance to target height, severity of GHD and occurrence of multiple pituitary hormone deficiencies had a positive effect (p < 0.01) on the calculated HV SDS. When applying the KIGS targets for severe iGHD, mean HV SDS was close to zero (-0.09 ± 0.84). Conclusion: The developed age-specific growth response curves enable rapid identification of poor response to first-year GH treatment in prepubertal iGHD children. Our results validate the published growth targets derived from the KIGS database.

Optimal nitrogen application rates for three intensively-managed hardwood tree species in the southeastern USA

Forest production can be limited by nutrient and water availability, and tree species are expected to respond differently to fertilization and irrigation. Despite these common expectations, multi-species comparisons are rare, especially ones implementing a range of fertilization rates crossed with irrigation. This study compares the response of three forest hardwood species to numerous nitrogen (N) fertilization levels and water availability using a novel non-replicated technique. A range of N levels was included to determine how N affected the growth response curve, and statistical procedures for comparing these non-linear response functions are presented. We used growth and yield data to calculate the Land Expectation Value (LEV) for these intensive management treatments, and to determine the optimal growing conditions (accounting for tree productivity and grower expenses). To accomplish these objectives, we used a series of cottonwood, sycamore, and sweetgum plots that received a range of N fertilization with or without irrigation. Regression is an economical approach to define treatment responses in large-scale experiments, and we recommend >3 treatment levels so the response of any single plot does not disproportionally influence the line. The non-replicated plots showed a strong positive N response below 150kgNha−1yr−1, beyond which little response was observed. However, different amounts of fertilization were required for the greatest biomass accumulation rate in each tree species. Cottonwood and sycamore growth was optimized with less than 150kgNha−1yr−1 while sweetgum growth was optimized with less than 100kgNha−1yr−1. Results from this experiment should be representative of many of the nutrient-poor soils in the Coastal Plain in the southeastern USA. The LEVs were not positive for any treatment×genotype combination tested when using irrigation or liquid fertilizer, but our analysis showed that several non-irrigated treatments in sycamore and sweetgum did result in positive LEVs when fertilized with granular urea.

Impact of tricyclazole and azoxystrobin on growth, sporulation and secondary infection of the rice blast fungus, Magnaporthe oryzae

Rice blast, caused by Magnaporthe oryzae B. Couch sp. nov., is one of the most destructive rice diseases worldwide, causing substantial yield losses every year. In Italy, its management is based mainly on the use of two fungicides, azoxystrobin and tricyclazole, that restrain the disease progress. The aim of this study was to investigate and compare the inhibitory effects of the two fungicides on the growth, sporulation and secondary infection of M. oryzae. Magnaporthe oryzae mycelium growth was inhibited at low concentrations of azoxystrobin and relatively high concentrations of tricyclazole, while sporulation was more sensitive to both fungicides and was affected at similarly low doses. Furthermore, infection efficiency of conidia obtained from mycelia exposed to tricyclazole was affected to a higher extent than for conidia produced on azoxystrobin-amended media, even though germination of such conidia was reduced after azoxystrobin treatment. This study presents for the first time detailed azoxystrobin and tricyclazole growth-response curves for M. oryzae mycelium growth and sporulation. Furthermore, high efficacy of tricyclazole towards inhibition of sporulation and secondary infection indicates an additional possible mode of action of this fungicide that is different from inhibition of melanin biosynthesis.

Differential effects of radio frequency magnetic fields in vitro and in vivo

Differential effects of RF magnetic fields in vitro and in vivoBackgroundThe present study investigates effects of radio frequency (RF) magnetic fields in the range 1–15 MHz on growth of cancer cells in vitro and in mice models. Most biomolecules have hyperfine splitting constants ranging from 0.1–10 MHz, which gives the basis for the chosen frequencies.MethodsFor in vitro experiments, fibrosarcoma cell line was treated 15 minutes a day with a combination of magnetic fields: 45 μT static fields in perpendicular and at 40 degrees to an RF signal. The exposures to an RF signal ranging from 5–10 MHz were conducted at a specific absorption rate (SAR) of 0.001, 0.01, 0.05 and 0.2 W/kg using continuous waves (CW). For in vivo experiments, mice with fibrosarcoma and pancreatic tumors were exposed continuously to low‐level static magnetic fields (0.5–2 μT) and a combination of 45 μT static fields in perpendicular to 10 MHz. All controls were exposed to the geomagnetic field (45 μT).ResultsA growth response curve as a function of SAR level is obtained indicating distinct effects for the SAR range used: inhibition of cellular proliferation is obtained for SAR level of 0.001 W/kg; SAR levels of 0.05 and 0.2 W/kg enhances proliferation in vitro. In vivo, 10 MHz magnetic fields inhibit tumor growth in mice as much as 35 percent on day 18 of exposure.ConclusionWe have shown that even a physically weak magnetic field can alter cellular growth. RF magnetic fields modulated proliferation of cancer cells both in vitro and in vivo. The exposure levels were below standard threshold levels for thermal effects due to electromagnetic radiation.

Viability of culturing pink shrimp Farfantepenaeus duorarum in low-salinity groundwater from the Yucatán Peninsula (SE, México)

In the Gulf of Mexico constraints linked to the supply of post-larvae (PL) and legal pressures associated with the introduction of a non-native species have been the motives behind research on the aquaculture of the native shrimp. In the present study, the growth and survival of 25-day-post-larvae (PL-25) of the pink shrimp Farfantepenaeus duorarum in saline groundwaters were evaluated. During the experiment the shrimps were acclimated from 36 psu to 5 psu utilizing various acclimation times ( T1 = 38 h, T2 = 42 h, and T3 = 45 h) with a variable rate of salinity reduction ( T1 = 9.9% h − 1 , T2 = 11.8% h − 1 , and T3 = 11.4% h − 1 ). After a 1-day acclimation period there were no differences ( P > 0.05) in survival between treatments (80.7 ± 3.5%). The salinity reduction rate of T1 (low acclimation time) was selected to acclimatize the PL for the nursery experiment due to the high survival rate recorded after the salinity stress test. During the nursery experiment, shrimp at a density of 80 PL m − 2 had the highest growth rate (20 mg week − 1 ) ( F (2,9) = 10.73; P < 0.05) and survival rate (79%) ( F (2,9) = 4.93; P < 0.05) in comparison to other densities (150 PL m − 2 ; 250 PL m − 2 ). The PL growth was adjusted to a non-linear regression function (0.030 * e (0.035 * d)). Shrimp at 80 PL m − 2 ( t = 0.87) and 150 PL m − 2 ( t = 1.54) showed isometric growth (Ho = b = 3). Temperature was the only environmental variable that explained the most consecutive additional variance (80.1%) in the PL weight. The temperature–growth response curve was fitted to a generalized additive model (GAM). Results from this research demonstrate that F. duorarum (PL-25) can be successfully acclimated to low-salinity (5 psu) conditions with a high percentage of survival and an acceptable growth rate in the nursery phase (45 days). In the future efforts should be made to improve survival at higher densities in order to make production profitable.

Effects of microzooplankton growth and trophic interactions on herbivory in coastal and offshore environments

We performed serial dilution experiments to estimate rates of gross phytoplankton growth (μ) and grazing mortality (m) in both eutrophic (Corpus Christi Bay, Texas, USA) and olig- otrophic (offshore Gulf of Mexico) waters. Two parallel experiments were performed in both environ- ments, with seawater pre-screened through 153 or 25 µm mesh to observe the responses of microzoo- plankton (MZP) to dilution treatments. MZP biomass changed over the duration of the experimental incubations; in several treatments, MZP net growth rates were >1 d -1 . Patterns of growth varied between dilutions and initial screening size. In the eutrophic system, the ratio of phytoplankton graz- ing mortality rate to gross phytoplankton growth rate (m/μ) was 1.10 ± 0.54 (mean ± SD) versus 0.41 ± 0.65 when screened through 153 and 25 µm mesh, respectively. This difference was attributed to cas- cading trophic interactions among MZP size groups leading to suppression of the primary herbivores in the 25 µm fraction and, in turn, a lower value of m. A food web model consisting of multiple trophic levels was constructed to examine the role of MZP growth and trophic interactions on measurements of μ and m. The model, using 3 interacting groups of MZP, was able to reproduce experimental results. Model simulations demonstrated that MZP growth during incubation leads to an overestima- tion of m. Non-linearity in the phytoplankton growth response curves was due to MZP growth and trophic interactions in these model simulations, as variable feeding responses were not incorporated into the models. Trophic interactions among MZP can provide context to measurements of μ and m and insight into microbial food web efficiency.

Growth and mortality rates of the fan mussel Pinna nobilis in Lake Vouliagmeni (Korinthiakos Gulf, Greece): a generalized additive modelling approach

The temporal patterns and the effect of shell size and depth on growth and mortality rates of the endangered fan mussel Pinna nobilis were investigated in the marine Lake Vouliagmeni (Korinthiakos Gulf, Greece). A total of 160 individuals were tagged and monitored monthly for a period of 17 months. At each visit, the size of the tagged individuals (shell width, w) was measured in situ and recorded. Any mortality event was also recorded and attributed to natural causes or (illegal) fishing. Growth and mortality rates were modeled with generalized additive models, which are non-parametric flexible models that free the researcher from the limiting concept of a strict parametric shape. The use of GAMs allowed the exploration of shapes of growth and mortality response curves in relation to predictor variables and allowed the fitting of statistical models that better agree with ecological theory. Growth rates had a seasonal pattern, with an extended period of very slow growth between late autumn and early spring, i.e., during the cold season, another short period of slow growth during August (when water temperatures reached their maximum values exceeding 29°C), and a peak in growth rates during late spring–early summer, probably related to an optimum combination of temperature and food availability. Growth rates varied with shell size, with a peak at w ∼4.5 cm, followed by a sharp decline to an approximately constant level, with sizes ranging from 9 to 15 cm, and a further decline with larger sizes down to almost zero for w > 20 cm. Growth rates did not vary substantially with depth. Although P. nobilis is a protected species in the EU and its fishing is strictly prohibited, fishing mortality was very high in Lake Vouliagmeni (much greater than natural mortality), especially during the hot season when the lake was crowded by summer visitors. The fan mussels were poached exclusively by free-diving and due to the high turbidity of the lake’s water, fishing mortality was higher in shallow areas (and mostly for large individuals) and was practically zero at depths >9 m. Due to fishing mortality, a size segregation of P. nobilis was observed in the lake: large individuals were restricted to deeper areas, while young and small individuals were more abundant in shallow areas where there was preferential recruitment. Natural mortality was strikingly size dependent and P. nobilis suffered high natural mortality during the first year of life; the probability of death by natural causes quickly diminished as the fan mussels grew in size. No depth-related differences in natural mortality were found.

GDNF selectively promotes regeneration of injury-primed sensory neurons in the lesioned spinal cord

Axonal regeneration within the CNS fails due to the growth inhibitory environment and the limited intrinsic growth capacity of injured neurons. Injury to DRG peripheral axons induces expression of growth associated genes including members of the glial-derived neurotrophic factor (GDNF) signaling pathway and “preconditions” the injured cells into an active growth state, enhancing growth of their centrally projecting axons. Here, we show that preconditioning DRG neurons prior to culturing increased neurite outgrowth, which was further enhanced by GDNF in a bell-shaped growth response curve. In vivo, GDNF delivered directly to DRG cell bodies facilitated the preconditioning effect, further enhancing axonal regeneration beyond spinal cord lesions. Consistent with the in vitro results, the in vivo effect was seen only at low GDNF concentrations. We conclude that peripheral nerve injury upregulates GDNF signaling pathway components and that exogenous GDNF treatment selectively promotes axonal growth of injury-primed sensory neurons in a concentration-dependent fashion.

Biosurfactants are involved in the biological control ofVerticilliummicrosclerotia byPseudomonasspp.

To examine the effect of previously described bacterial antagonists on the viability of Verticillium microsclerotia in vitro and to elucidate the possible modes of action of bacterial strains in the suppression of Verticillium microsclerotia viability. A microplate assay was developed to test the suppressive effect of well-defined Pseudomonas spp. on the viability of Verticillium microsclerotia in vitro. Experiments using phenazine- and biosurfactant-deficient mutants indicated that biosurfactants and phenazine-1-carboxylic acid play a role in the suppression of microsclerotia viability by Pseudomonas spp. In addition, microsclerotia colonization tests revealed that Pseudomonas spp. are able to colonize the surface of the microsclerotia, but not the inner matrix. Growth response curves showed that the population levels of Pseudomonas spp. increased when they were in the vicinity of Verticillium microsclerotia, indicating that Pseudomonas spp. may utilize nutrients from the microsclerotia for their growth. Pseudomonas spp. seem to be good candidates for Verticilllium microsclerotia biocontrol. Biosurfactant production is one of the main mechanisms involved in their mode of action. This line of work may contribute to a better understanding of biological control agents and their working mechanisms.

Understanding the low-temperature limitations to forest growth through calibration of a forest dynamics model with tree-ring data

The sensitivity of altitudinal and latitudinal tree-line ecotones to climate change, particularly that of temperature, has received much attention. To improve our understanding of the factors affecting tree-line position, we used the spatially explicit dynamic forest model TreeMig. Although well-suited because of its landscape dynamics functions, TreeMig features a parabolic temperature growth response curve, which has recently been questioned, and the species parameters are not specifically calibrated for cold temperatures. Our main goals were to improve the theoretical basis of the temperature growth response curve in the model and develop a method for deriving that curve's parameters from tree-ring data. We replaced the parabola with an asymptotic curve, calibrated for the main species at the subalpine (Swiss Alps: Pinus cembra, Larix decidua, Picea abies) and boreal (Fennoscandia: Pinus sylvestris, Betula pubescens, P. abies) tree-lines. After fitting new parameters, the growth curve matched observed tree-ring widths better. For the subalpine species, the minimum degree-day sum allowing growth (kDDMin) was lowered by around 100 degree-days; in the case of Larix, the maximum potential ring-width was increased to 5.19 mm. At the boreal tree-line, the kDDMin for P. sylvestris was lowered by 210 degree-days and its maximum ring-width increased to 2.943 mm; for Betula (new in the model) kDDMin was set to 325 degree-days and the maximum ring-width to 2.51 mm; the values from the only boreal sample site for Picea were similar to the subalpine ones, so the same parameters were used. However, adjusting the growth response alone did not improve the model's output concerning species’ distributions and their relative importance at tree-line. Minimum winter temperature (MinWiT, mean of the coldest winter month), which controls seedling establishment in TreeMig, proved more important for determining distribution. Picea, P. sylvestris and Betula did not previously have minimum winter temperature limits, so these values were set to the 95th percentile of each species’ coldest MinWiT site (respectively −7, −11, −13). In a case study for the Alps, the original and newly calibrated versions of TreeMig were compared with biomass data from the National Forest Inventory (NFI). Both models gave similar, reasonably realistic results. In conclusion, this method of deriving temperature responses from tree-rings works well. However, regeneration and its underlying factors seem more important for controlling species’ distributions than previously thought. More research on regeneration ecology, especially at the upper limit of forests, is needed to improve predictions of tree-line responses to climate change further.

Activities of mixtures of soil‐applied herbicides with different molecular targets

The joint action of soil-applied herbicide mixtures with similar or different modes of action has been assessed by using the additive dose model (ADM). The herbicides chlorsulfuron, metsulfuron-methyl, pendimethalin and pretilachlor, applied either singly or in binary mixtures, were used on rice (Oryza sativa L.). The growth (shoot) response curves were described by a logistic dose-response model. The ED50 values and their corresponding standard errors obtained from the response curves were used to test statistically if the shape of the isoboles differed from the reference model (ADM). Results showed that mixtures of herbicides with similar molecular targets, i.e. chlorsulfuron and metsulfuron (acetolactate synthase (ALS) inhibitors), and with different molecular targets, i.e. pendimethalin (microtubule assembly inhibitor) and pretilachlor (very long chain fatty acids (VLCFAs) inhibitor), followed the ADM. Mixing herbicides with different molecular targets gave different results depending on whether pretilachlor or pendimethalin was involved. In general, mixtures of pretilachlor and sulfonylureas showed synergistic interactions, whereas mixtures of pendimethalin and sulfonylureas exhibited either antagonistic or additive activities. Hence, there is a large potential for both increasing the specificity of herbicides by using mixtures and lowering the total dose for weed control, while at the same time delaying the development of herbicide resistance by using mixtures with different molecular targets.

Effect of Magnesium Deficiency on Pepper Growth Parameters: Implications for Determination of Magnesium‐Critical Value

In order to improve determinations of nutrient critical levels using growth response curves, a detailed study of magnesium (Mg) deficiency on pepper (Capsicum annuum L.) biomass allocation was performed. For each growth parameter, data were fitted using the modified Mitscherlich's model and Mg‐critical level was calculated. Under Mg‐deficiency, pepper plants showed a decrease in their relative growth rate (RGR), total dry weight (DW), stem and root mass fractions (SMF and RMF), total leaf area, specific leaf area (SLA), and unit leaf rate (ULR), whereas leaf mass fraction (LMF) and shoot to root ratio increased. Growth response coefficient (GRC) analysis indicated that the decrease in RGR was mainly due to a decrease in ULR. When the interval time between two harvests was ≥10 days, determination of Mg‐critical level (x c ) using the modified Mitscherlich's model showed that the best growth parameter for early detection of Mg‐deficiency in pepper plants was total DW (x c ≈ 0.21%), whereas other parameters underestimated Mg‐critical level.