Showing papers by "Ben-Gurion University of the Negev published in 2012"

Guidelines for the use and interpretation of assays for monitoring autophagy

Abstract: In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.

Plant Species Richness and Ecosystem Multifunctionality in Global Drylands

Abstract: Experiments suggest that biodiversity enhances the ability of ecosystems to maintain multiple functions, such as carbon storage, productivity, and the buildup of nutrient pools (multifunctionality). However, the relationship between biodiversity and multifunctionality has never been assessed globally in natural ecosystems. We report here on a global empirical study relating plant species richness and abiotic factors to multifunctionality in drylands, which collectively cover 41% of Earth’s land surface and support over 38% of the human population. Multifunctionality was positively and significantly related to species richness. The best-fitting models accounted for over 55% of the variation in multifunctionality and always included species richness as a predictor variable. Our results suggest that the preservation of plant biodiversity is crucial to buffer negative effects of climate change and desertification in drylands.

Andromaly: a behavioral malware detection framework for android devices

Abstract: This article presents Andromaly--a framework for detecting malware on Android mobile devices. The proposed framework realizes a Host-based Malware Detection System that continuously monitors various features and events obtained from the mobile device and then applies Machine Learning anomaly detectors to classify the collected data as normal (benign) or abnormal (malicious). Since no malicious applications are yet available for Android, we developed four malicious applications, and evaluated Andromaly's ability to detect new malware based on samples of known malware. We evaluated several combinations of anomaly detection algorithms, feature selection method and the number of top features in order to find the combination that yields the best performance in detecting new malware on Android. Empirical results suggest that the proposed framework is effective in detecting malware on mobile devices in general and on Android in particular.

The fundamental link between pneumococcal carriage and disease

Abstract: Streptococcus pneumoniae (pneumococcus) is a major cause of worldwide mortality and morbidity, and to a large extent is vaccine-preventable. Nasopharyngeal carriage of pneumococcus precedes disease and is the source of pneumococcal spread between people. The use of vaccine effect on carriage as part of the vaccine licensure and post-vaccine introduction evaluation could facilitate and expand the licensure of new, life-saving pneumococcal vaccines and enable a comprehensive estimate of population effects after vaccine introduction. The authors provide a review of the evidence supporting pneumococcal carriage at the individual level as an immediate and necessary precursor to pneumococcal disease. Based on such a causal link between carriage and disease, the authors emphasize the role of information on pneumococcal carriage in vaccine trials and in public health decision-making.

Conflict-based search for optimal multi-agent path finding

Abstract: In the multi agent path finding problem (MAPF) paths should be found for several agents, each with a different start and goal position such that agents do not collide. Previous optimal solvers applied global A*-based searches. We present a new search algorithm called Conflict Based Search (CBS). CBS is a two-level algorithm. At the high level, a search is performed on a tree based on conflicts between agents. At the low level, a search is performed only for a single agent at a time. In many cases this reformulation enables CBS to examine fewer states than A* while still maintaining optimality. We analyze CBS and show its benefits and drawbacks. Experimental results on various problems shows a speedup of up to a full order of magnitude over previous approaches.

Human Ageing Genomic Resources: Integrated databases and tools for the biology and genetics of ageing

Abstract: The Human Ageing Genomic Resources (HAGR, http://genomics.senescence.info) is a freely available online collection of research databases and tools for the biology and genetics of ageing. HAGR features now several databases with high-quality manually curated data: (i) GenAge, a database of genes associated with ageing in humans and model organisms; (ii) AnAge, an extensive collection of longevity records and complementary traits for >4000 vertebrate species; and (iii) GenDR, a newly incorporated database, containing both gene mutations that interfere with dietary restriction-mediated lifespan extension and consistent gene expression changes induced by dietary restriction. Since its creation about 10 years ago, major efforts have been undertaken to maintain the quality of data in HAGR, while further continuing to develop, improve and extend it. This article briefly describes the content of HAGR and details the major updates since its previous publications, in terms of both structure and content. The completely redesigned interface, more intuitive and more integrative of HAGR resources, is also presented. Altogether, we hope that through its improvements, the current version of HAGR will continue to provide users with the most comprehensive and accessible resources available today in the field of biogerontology.

Implanted Biofuel Cell Operating in a Living Snail

Abstract: Implantable biofuel cells have been suggested as sustainable micropower sources operating in living organisms, but such bioelectronic systems are still exotic and very challenging to design. Very few examples of abiotic and enzyme-based biofuel cells operating in animals in vivo have been reported. Implantation of biocatalytic electrodes and extraction of electrical power from small living creatures is even more difficult and has not been achieved to date. Here we report on the first implanted biofuel cell continuously operating in a snail and producing electrical power over a long period of time using physiologically produced glucose as a fuel. The “electrified” snail, being a biotechnological living “device”, was able to regenerate glucose consumed by biocatalytic electrodes, upon appropriate feeding and relaxing, and then produce a new “portion” of electrical energy. The snail with the implanted biofuel cell will be able to operate in a natural environment, producing sustainable electrical micropower f...

Meta-Analysis of Efficacy and Safety of New Oral Anticoagulants ( Dabigatran , Rivaroxaban , Apixaban ) Versus Warfarin in Patients With Atrial Fibrillation

Abstract: New oral anticoagulants, including apixaban, dabigatran, and rivaroxaban, have been developed as alternatives to warfarin, the standard oral anticoagulation therapy for patients with atrial fibrillation (AF). A systematic review and meta-analysis of randomized controlled trials was performed to compare the efficacy and safety of new oral anticoagulants to those of warfarin in patients with AF. The published research was systematically searched for randomized controlled trials of >1 year in duration that compared new oral anticoagulants to warfarin in patients with AF. Random-effects models were used to pool efficacy and safety data across randomized controlled trials. Three studies, including 44,563 patients, were identified. Patients randomized to new oral anticoagulants had a decreased risk for all-cause stroke and systemic embolism (relative risk [RR] 0.78, 95% confidence interval [CI] 0.67 to 0.92), ischemic and unidentified stroke (RR 0.87, 95% CI 0.77 to 0.99), hemorrhagic stroke (RR 0.45, 95% CI 0.31 to 0.68), all-cause mortality (RR 0.88, 95% CI 0.82 to 0.95), and vascular mortality (RR 0.87, 95% CI 0.77 to 0.98). Randomization to a new oral anticoagulant was associated with a lower risk for intracranial bleeding (RR 0.49, 95% CI 0.36 to 0.66). Data regarding the risks for major bleeding (RR 0.88, 95% CI 0.71 to 1.09) and gastrointestinal bleeding (RR 1.25, 95% CI 0.91 to 1.72) were inconclusive. In conclusion, the new oral anticoagulants are more efficacious than warfarin for the prevention of stroke and systemic embolism in patients with AF. With a decreased risk for intracranial bleeding, they appear to have a favorable safety profile, making them promising alternatives to warfarin.

Executive Function and Falls in Older Adults: New Findings from a Five-Year Prospective Study Link Fall Risk to Cognition

Abstract: Background: Recent findings suggest that executive function (EF) plays a critical role in the regulation of gait in older adults, especially under complex and challenging conditions, and that EF deficits may, therefore, contribute to fall risk. The objective of this study was to evaluate if reduced EF is a risk factor for future falls over the course of 5 years of follow-up. Secondary objectives were to assess whether single and dual task walking abilities, an alternative window into EF, were associated with fall risk. Methodology/Main Results: We longitudinally followed 256 community-living older adults (age: 76.464.5 yrs; 61% women) who were dementia free and had good mobility upon entrance into the study. At baseline, a computerized cognitive battery generated an index of EF, attention, a closely related construct, and other cognitive domains. Gait was assessed during single and dual task conditions. Falls data were collected prospectively using monthly calendars. Negative binomial regression quantified risk ratios (RR). After adjusting for age, gender and the number of falls in the year prior to the study, only the EF index (RR: .85; CI: .74–.98, p=.021), the attention index (RR: .84; CI: .75–.94, p=.002) and dual tasking gait variability (RR: 1.11; CI: 1.01–1.23; p=.027) were associated with future fall risk. Other cognitive function measures were not related to falls. Survival analyses indicated that subjects with the lowest EF scores were more likely to fall sooner and more likely to experience multiple falls during the 66 months of follow-up (p,0.02). Conclusions/Significance: These findings demonstrate that among community-living older adults, the risk of future falls was predicted by performance on EF and attention tests conducted 5 years earlier. The present results link falls among older adults to cognition, indicating that screening EF will likely enhance fall risk assessment, and that treatment of EF may reduce fall risk.

Honesty Requires Time (and Lack of Justifications)

Abstract: Recent research suggests that refraining from cheating in tempting situations requires self-control, which indicates that serving self-interest is an automatic tendency. However, evidence also suggests that people cheat to the extent that they can justify their unethical behavior to themselves. To merge these different lines of research, we adopted a dual-system approach that distinguished between the intuitive and deliberative cognitive systems. We suggest that for people to restrict their dishonest behavior, they need to have enough time and no justifications for self-serving unethical behavior. We employed an anonymous die-under-cup task in which participants privately rolled a die and reported the outcome to determine their pay. We manipulated the time available for participants to report their outcome (short vs. ample). The results of two experiments support our prediction, revealing that the dark side of people’s automatic self-serving tendency may be overcome when time to decide is ample and privat...

Pathophysiology of the Neurovascular Unit: Disease Cause or Consequence?:

Abstract: Pathophysiology of the neurovascular unit (NVU) is commonly seen in neurological diseases. The typical features of NVU pathophysiology include tissue hypoxia, inflammatory and angiogenic activation, as well as initiation of complex molecular interactions between cellular (brain endothelial cells, astroctyes, pericytes, inflammatory cells, and neurons) and acellular (basal lamina) components of the NVU, jointly resulting in increased blood-brain barrier permeability, brain edema, neurovascular uncoupling, and neuronal dysfunction and damage. The evidence of important role of the brain vascular compartment in disease pathogenesis has elicited the debate whether the primary vascular events may be a cause of the neurological disease, as opposed to a mere participant recruited by a primary neuronal origin of pathology? Whereas some hereditary and acquired cerebral angiopathies could be considered a primary cause of neurological symptoms of the disease, the epidemiological studies showing a high degree of comorbidity among vascular disease and dementias, including Alzheimer's disease, as well as migraine and epilepsy, suggested that primary vascular pathology may be etiological factor causing neuronal dysfunction or degeneration in these diseases. This review focuses on recent hypotheses and evidence, suggesting that pathophysiology of the NVU may be initiating trigger for neuronal pathology and subsequent neurological manifestations of the disease.

Go Green! Should Environmental Messages Be So Assertive?

Abstract: Environmental communications often contain assertive commands, even though research in consumer behavior, psycholinguistics, and communications has repeatedly shown that gentler phrasing is more effective when seeking consumer compliance. This article shows that the persuasiveness of assertive language depends on the perceived importance of the issue at hand: Recipients respond better to pushy requests in domains that they view as important, but they need more suggestive appeals when they lack initial conviction. The authors examine this effect in three laboratory studies and one field experiment using Google AdWords. Their findings refer to various environmental contexts (i.e., economizing water, recycling plastic containers, reducing air and sea pollution). The key implication of these findings is that issue importance needs to be carefully assessed (or affected) before the language of effective environmental campaigns can be selected.

Missense mutations in the sodium-gated potassium channel gene KCNT1 cause severe autosomal dominant nocturnal frontal lobe epilepsy

Abstract: We performed genomic mapping of a family with autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and intellectual and psychiatric problems, identifying a disease-associated region on chromosome 9q34.3. Whole-exome sequencing identified a mutation in KCNT1, encoding a sodium-gated potassium channel subunit. KCNT1 mutations were identified in two additional families and a sporadic case with severe ADNFLE and psychiatric features. These findings implicate the sodium-gated potassium channel complex in ADNFLE and, more broadly, in the pathogenesis of focal epilepsies.

Overview and introduction: The blood–brain barrier in health and disease

Abstract: This article introduces the special issue on "Blood-Brain Barrier and Epilepsy." We review briefly current understanding of the structure and function of the blood-brain barrier (BBB), including its development and normal physiology, and ways in which it can be affected in pathology. The BBB formed by the endothelium of cerebral blood vessels is one of three main barrier sites protecting the central nervous system (CNS). The barrier is not a rigid structure, but a dynamic interface with a range of interrelated functions, resulting from extremely effective tight junctions, transendothelial transport systems, enzymes, and regulation of leukocyte permeation, which thereby generates the physical, transport, enzymatic, and immune regulatory functions of the BBB. The brain endothelial cells are important components of a "modular" structure, the neurovascular unit (NVU), with several associated cell types and extracellular matrix components. Modern methods have helped in identifying a range of proteins involved in barrier structure and function, and recent studies have revealed important stages, cell types, and signaling pathways important in BBB development. There is a growing list of CNS pathologies showing BBB dysfunction, with strong evidence that this can play a major role in certain disease etiologies. The articles that follow in this issue summarize in more detail reports and discussions of the recent international meeting on "BBB in Neurological Dysfunctions," which took place recently at Ben-Gurion University of the Negev Desert Campus (Beer-Sheva, Israel), focusing on the link between experimental and clinical studies, and the ways in which these lead to improved drug treatments.

A search-classify approach for cluttered indoor scene understanding

Abstract: We present an algorithm for recognition and reconstruction of scanned 3D indoor scenes. 3D indoor reconstruction is particularly challenging due to object interferences, occlusions and overlapping which yield incomplete yet very complex scene arrangements. Since it is hard to assemble scanned segments into complete models, traditional methods for object recognition and reconstruction would be inefficient. We present a search-classify approach which interleaves segmentation and classification in an iterative manner. Using a robust classifier we traverse the scene and gradually propagate classification information. We reinforce classification by a template fitting step which yields a scene reconstruction. We deform-to-fit templates to classified objects to resolve classification ambiguities. The resulting reconstruction is an approximation which captures the general scene arrangement. Our results demonstrate successful classification and reconstruction of cluttered indoor scenes, captured in just few minutes.

Detecting unknown malicious code by applying classification techniques on OpCode patterns

Abstract: In previous studies classification algorithms were employed successfully for the detection of unknown malicious code. Most of these studies extracted features based on byte n-gram patterns in order to represent the inspected files. In this study we represent the inspected files using OpCode n-gram patterns which are extracted from the files after disassembly. The OpCode n-gram patterns are used as features for the classification process. The classification process main goal is to detect unknown malware within a set of suspected files which will later be included in antivirus software as signatures. A rigorous evaluation was performed using a test collection comprising of more than 30,000 files, in which various settings of OpCode n-gram patterns of various size representations and eight types of classifiers were evaluated. A typical problem of this domain is the imbalance problem in which the distribution of the classes in real life varies. We investigated the imbalance problem, referring to several real-life scenarios in which malicious files are expected to be about 10% of the total inspected files. Lastly, we present a chronological evaluation in which the frequent need for updating the training set was evaluated. Evaluation results indicate that the evaluated methodology achieves a level of accuracy higher than 96% (with TPR above 0.95 and FPR approximately 0.1), which slightly improves the results in previous studies that use byte n-gram representation. The chronological evaluation showed a clear trend in which the performance improves as the training set is more updated.

Functional Architecture of the Nuclear Pore Complex

Abstract: The nuclear pore complex (NPC) is the sole gateway between the nucleus and the cytoplasm. NPCs fuse the inner and outer nuclear membranes to form aqueous translocation channels that allow the free diffusion of small molecules and ions, as well as receptor-mediated transport of large macromolecules. The NPC regulates nucleocytoplasmic transport of macromolecules, utilizing soluble receptors that identify and present cargo to the NPC, in a highly selective manner to maintain cellular functions. The NPC is composed of multiple copies of approximately 30 different proteins, termed nucleoporins, which assemble to form one of the largest multiprotein assemblies in the cell. In this review, we address structural and functional aspects of this fundamental cellular machinery.

Magnetic properties of electron-doped La0.23Ca0.77MnO3 nanoparticles

Abstract: Magnetic properties of electron-doped La0.23Ca0.77MnO3 manganite nanoparticles, with average size of 12 and 60 nm, prepared by the glycine–nitrate method, have been investigated in the temperature range 5–300 K and magnetic fields up to 90 kOe. It is suggested that weak ferromagnetic moment results from ferromagnetic shells of the basically antiferromagnetic nanoparticles and from domains of frustrated disordered phase in the core. Assumption of two distinct sources of ferromagnetism is supported by the appearance of two independent ferromagnetic contributions in the fit of the T 3/2 Bloch law to spontaneous magnetization. The ferromagnetic components, which are more pronounced in smaller particles, occupy only a small fraction of the nanoparticle volume and the antiferromagnetic ground state remains stable. It is found that the magnetic hysteresis loops following field cooled processes, display size-dependent horizontal and vertical shifts, namely, exhibiting exchange bias effect. Time-dependent magnetization dynamics demonstrating two relaxation rates were observed at constant magnetic fields upon cooling to T < 100 K.

Economic games on the internet: the effect of $1 stakes.

Abstract: Online labor markets such as Amazon Mechanical Turk (MTurk) offer an unprecedented opportunity to run economic game experiments quickly and inexpensively. Using Mturk, we recruited 756 subjects and examined their behavior in four canonical economic games, with two payoff conditions each: a stakes condition, in which subjects' earnings were based on the outcome of the game (maximum earnings of $1); and a no-stakes condition, in which subjects' earnings are unaffected by the outcome of the game. Our results demonstrate that economic game experiments run on MTurk are comparable to those run in laboratory settings, even when using very low stakes.

Scientific Utopia: I. Opening Scientific Communication

Abstract: Existing norms for scientific communication are rooted in anachronistic practices of bygone eras making them needlessly inefficient. We outline a path that moves away from the existing model of scientific communication to improve the efficiency in meeting the purpose of public science—knowledge accumulation. We call for six changes: (a) full embrace of digital communication; (b) open access to all published research; (c) disentangling publication from evaluation; (d) breaking the “one article, one journal” model with a grading system for evaluation and diversified dissemination outlets; (e) publishing peer review; and (f) allowing open, continuous peer review. We address conceptual and practical barriers to change and provide examples showing how the suggested practices are being used already. The critical barriers to change are not technical or financial; they are social. Although scientists guard the status quo, they also have the power to change it.

A win-win solution in oral delivery of lipophilic drugs: supersaturation via amorphous solid dispersions increases apparent solubility without sacrifice of intestinal membrane permeability.

Abstract: Recently, we have revealed a trade-off between solubility increase and permeability decrease when solubility-enabling oral formulations are employed. We have shown this trade-off phenomenon to be ubiquitous, and to exist whenever the aqueous solubility is increased via solubilizing excipients, regardless if the mechanism involves decreased free fraction (cyclodextrins complexation, surfactant micellization) or simple cosolvent solubilization. Discovering a way to increase drug solubility without concomitant decreased permeability represents a major advancement in oral delivery of lipophilic drugs and is the goal of this work. For this purpose, we sought to elucidate the solubility-permeability interplay when increased apparent solubility is obtained via supersaturation from an amorphous solid dispersion (ASD) formulation. A spray-dried ASD of the lipophilic drug progesterone was prepared in the hydrophilic polymer hydroxypropyl methylcellulose acetate succinate (HPMC-AS), which enabled supersaturation up to 4× the crystalline drug's aqueous solubility (8 μg/mL). The apparent permeability of progesterone from the ASD in HPMC-AS was then measured as a function of increasing apparent solubility (supersaturation) in the PAMPA and rat intestinal perfusion models. In contrast to previous cases in which apparent solubility increases via cyclodextrins, surfactants, and cosolvents resulted in decreased apparent permeability, supersaturation via ASD resulted in no decrease in apparent permeability with increasing apparent solubility. As a result, overall flux increased markedly with increasing apparent solubility via ASD as compared to the other formulation approaches. This work demonstrates that supersaturation via ASDs has a subtle yet powerful advantage over other solubility-enabling formulation approaches. That is, increased apparent solubility may be achieved without the expense of apparent intestinal membrane permeability. Thus, supersaturation via ASDs presents a markedly increased opportunity to maximize overall oral drug absorption.

Living battery – biofuel cells operating in vivo in clams

Abstract: Biofuel cells implanted in living clams and producing sustainable electrical power in vivo were integrated in batteries. The “electrified” clams, being biotechnological living “devices”, were able to generate electrical power using physiologically produced glucose as the fuel. The activity of the living batteries was dependent on the environmental conditions which are affecting physiological processes in clams. The living batteries generated open circuitry voltage (Voc), short circuitry current (Isc) and maximum power (Pmax) of ca. 800 mV, 25 μA, 5.2 μW and ca. 360 mV, 300 μA, 37 μW for the serial and parallel connections of 3 “electrified” clams, respectively. A clam-battery was connected to a capacitor which was charged up to 240 mV providing accumulation of electrical energy up to 28.8 mJ. Discharging the capacitor on an electrical motor resulted in the motor rotation. The “electrified” clams integrated in batteries demonstrated the possibility of activating electrical/electronic devices using energy produced in vivo.

Current challenges in compound-specific stable isotope analysis of environmental organic contaminants

Abstract: Compound-specific stable-isotope analysis (CSIA) has greatly facilitated assessment of sources and transformation processes of organic pollutants. Multielement isotope analysis is one of the most promising applications of CSIA because it even enables distinction of different transformation pathways. This review introduces the essential features of continuous-flow isotope-ratio mass spectrometry (IRMS) and highlights current challenges in environmental analysis as exemplified for the isotopes of nitrogen, hydrogen, chlorine, and oxygen. Strategies and recent advances to enable isotopic measurements of polar contaminants, for example pesticides or pharmaceuticals, are discussed with special emphasis on possible solutions for analysis of low concentrations of contaminants in environmental matrices. Finally, we discuss different levels of calibration and referencing and point out the urgent need for compound-specific isotope standards for gas chromatography–isotope-ratio mass spectrometry (GC–IRMS) of organic pollutants.

Tropical tree seedling growth responses to nitrogen, phosphorus and potassium addition

Abstract: Summary 1. Nutrients are a critical resource for plant growth, but the elements limiting growth in tropical forests have rarely been determined. 2. We investigated the influence of nitrogen (N), phosphorus (P), potassium (K) and micronutrients on seedling biomass and nutrient allocation in a factorial nutrient fertilization experiment in lowland tropical forest at the Barro Colorado Nature Monument, Panama. We also measured 8 years of herbivory and growth for 1800 seedlings. We sought to determine the identity of limiting elements and possible nutrient interactions. 3. The five study species were Alseis blackiana, Desmopsis panamensis, Heisteria concinna, Sorocea affinis and Tetragastris panamensis. Plants grew in deeply shaded understorey with a mean canopy openness of 4.9% (±0.7%; 1 SE). 4. Tissue N concentration increased by 11% with N addition. Tissue P concentration increased by 16% with P addition. Tissue K increased by 4% with K addition. K addition reduced root-to-shoot biomass ratio. There was no significant effect of fertilization on specific leaf area or leaf area ratio. 5. The proportion of leaves damaged and the mean level of damage by herbivory increased with P and K addition and showed a significant P · Ki nteraction. 6. Across all species and years, relative growth rate of height increased with K addition and with N and P in combination. Relative growth rate of leaf count trended 8.5% higher with K addition (P =0 .076). 7. We also added micronutrients in a parallel experiment. There was no effect of micronutrient addition on any seedling parameter. 8. Synthesis. K addition affected seedlings by enhancing tissue nutrient concentration, increasing herbivory, reducing root-to-shoot biomass ratio and increasing height growth. Additional effects of N or P on tissue chemistry, herbivory and growth offer support for the multiple limiting resources hypothesis. Our results suggest that seedling growth is limited by nutrients, especially K, even under highly shaded conditions in this lowland tropical forest.