Relations between bedtime parenting behaviors and temperament across 14 cultures.

Objectives: The present study examined parental sleep-supporting practices during toddlerhood in relation to temperament across 14 cultures. We hypothesized that passive sleep-supporting techniques (e.g., talking, cuddling), but not active techniques (e.g., walking, doing an activity together), would be associated with less challenging temperament profiles: higher Surgency (SUR) and Effortful Control (EC) and lower Negative Emotionality (NE), with fine-grained dimensions exhibiting relationships consistent with their overarching factors (e.g., parallel passive sleep-supporting approach effects for dimensions of NE). Methods: Caregivers (N = 841) across 14 cultures (M = 61 families per site) reported toddler (between 17 and 40 months of age; 52% male) temperament and sleep-supporting activities. Utilizing linear multilevel regression models and group-mean centering procedures, we assessed the role of between- and within-cultural variance in sleep-supporting practices in relation to temperament. Results: Both within-and between-culture differences in passive sleep-supporting techniques were associated with temperament attributes, (e.g., lower NE at the between-culture level; higher within-culture EC). For active techniques only within-culture effects were significant (e.g., demonstrating a positive association with NE). Adding sleep-supporting behaviors to the regression models accounted for significantly more between-culture temperament variance than child age and gender alone. Conclusion: Hypotheses were largely supported. Findings suggest parental sleep practices could be potential targets for interventions to mitigate risk posed by challenging temperament profiles (e.g., reducing active techniques that are associated with greater distress proneness and NE).

The porridge-like framework: A multidimensional guidance to support parents of children with developmental disabilities.

Parents of children with developmental disabilities face many daily challenges that can lead to emotional and affective problems, difficulties in caregiving, and partial mental representations about themselves and their children. The multi-faceted nature of these parents' needs requires a multi-component approach that should include the analysis of priority support goals and the planning of tailored therapeutic actions. Despite different types of validated interventions are available, the choice of the most appropriate strategy to pursue a family-centered approach to support parents of infants with developmental disabilities is not obvious. In this scenario, we propose a multi-dimensional model, the porridge-like framework of parenting. It considers three interrelated domains in parents' experience - affective (A), behavioral (B), and cognitive (C) aspects - that are intertwined with the specific degree of the child's impairment (D). This ABCD model may provide professionals with pragmatically valid guidance to plan and deliver family-centered healthcare interventions. By covering the multi-dimensional nature of parenting challenges, it provides clinicians with conceptual categories to recognize the specific needs and to choose the most suitable therapeutic action to address them. In addition, it aims to promote an ethical approach to family-centered rehabilitation for children with developmental disabilities, maximizing the potentials of a collaborative assessment approach.

More than words: methodological potentials of graphical elicitation with parents of preterm infants.

BACKGROUND: Word-based tools, such as interviews, can only partially provide access to the lived experience of parents of preterm infants. This study explores the lived experience of parents of preterm infants between 3 and 6 months after discharge by means of visual method (i.e., graphical elicitation). METHODS: A qualitative study with graphic elicitation analysis was used to assess the lived experience of four parental couples of very preterm infants in a home-based session occurred between 3 and 6 months after Neonatal Intensive Care Unit (NICU) discharge. RESULTS: The use of graphical elicitation revealed three dimensions of the experience of being parents of preterm infants: 1) different use of time-lining elements suggested a different involvement of cognitive and/or emotional coping mechanisms in facing the unexpected birth and NICU stay; 2) the explicit or implicit use of emotional graphical elements and words was suggestive of different degrees of openness to disclose their experience; 3) the role of textual elements in support or substitution of graphical elements indicated different levels of integration of cognitive and emotional representations. CONCLUSIONS: The use of visual methods holds the potentials for revealing specific aspects of the parental experience of preterm birth and NICU stay. The clinical implications of this approach are further discussed with reference to its potential implementation within parental support intervention.

Premature birth affects visual body representation and body schema in preterm children.

Research has demonstrated that from the first six months of life infants show early sensitivity to body visual features and rely on sensorimotor and proprioceptive inputs in forming representations of their own bodies. Premature birth interferes with typical exposition to visual, sensorimotor and proprioceptive stimulation, thus presumably affecting the development of body representations. Here, we tested this hypothesis by comparing the performance of preterm children with that of age-matched full-termchildren in two tasks assessing, respectively, visual body processing and body schema. We found that preterm children had spared configural processing but altered holistic processing of others' bodies and showed a general difficulty in expressing visuospatial judgements on body stimuli. Furthermore, body-centered visuospatial abilities were associated with specific impairments in operating object-based visuospatial transformations. The findings of this study indicate that preterm birth might interfere with the development of body representations at the levels of body visual perceptual processing and of body schema, with effects even on visuo-spatial abilities for non-bodily stimuli. Body-centered rehabilitative interventions should be proposed to preterm children in order to enhance visuo-spatial abilities and higher-level cognitive functions.

Evidence and Open Questions for the Use of Video-Feedback Interventions With Parents of Children With Neurodevelopmental Disabilities.

The Video-Feedback Intervention (VFI) is a technique aimed at promoting positive parenting that has been found to be supportive of child development and parent-child interaction in different at-risk and clinical populations. The application of VFI with parents of children with neurodevelopmental disabilities (ND; e.g., cerebral palsy, sensory and/or psychomotor delay, and genetic syndromes) is growing. Nonetheless, no systematic review is currently available documenting whether this type of intervention improves children's developmental outcomes (e.g., behavioral stability and cognitive abilities), parental caregiving skills (e.g., responsive parenting), and parental emotional well-being (e.g., depressive symptomatology). In the present mini-review, 212 VFI records were retrieved from three databases (i.e., PubMed, Scopus, and Web of Science), and 10 papers were finally included. Abstracted information included age, diagnosis, methodological aspects (timing, setting, and themes), and child/parent outcomes. Significant improvements from pre- to post-VFI were observed in all studies. Specifically, the VFIs were significantly associated with better children developmental outcomes and parental caregiving skills. Inconsistent findings emerged for the VFI effects on parental emotional well-being. Overall, the current mini-review supports the potential effectiveness of parent-focused VFI interventions for parents of children with ND, despite the presence of open questions that need to be addressed in future clinical trials.

Early Brain Damage Affects Body Schema and Person Perception Abilities in Children and Adolescents with Spastic Diplegia.

Early brain damage leading to cerebral palsy is associated to core motor impairments and also affects cognitive and social abilities. In particular, previous studies have documented specific alterations of perceptual body processing and motor cognition that are associated to unilateral motor deficits in hemiplegic patients. However, little is known about spastic diplegia (SpD), which is characterized by motorial deficits involving both sides of the body and is often associated to visuospatial, attentional, and social perception impairments. Here, we compared the performance of a sample of 30 children and adolescents with SpD (aged 7-18 years) and of a group of age-matched controls with typical development (TD) at two different tasks tapping on body representations. In the first task, we tested visual and motor imagery abilities as assessed, respectively, by the object-based mental rotation of letters and by the first-person transformations for whole-body stimuli. In the second task, we administered an inversion effect/composite illusion task to evaluate the use of configural/holistic processing of others' body. Additionally, we assessed social perception abilities in the SpD sample using the NEPSY-II battery. In line with previously reported visuospatial deficits, a general mental imagery impairment was found in SpD patients when they were engaged in both object-centered and first-person mental transformations. Nevertheless, a specific deficit in operating an own-body transformation emerged. As concerns body perception, while more basic configural processing (i.e., inversion effect) was spared, no evidence for holistic (i.e., composite illusion) body processing was found in the SpD group. NEPSY-II assessment revealed that SpD children were impaired in both the theory of mind and affect recognition subtests. Overall, these findings suggested that early brain lesions and biased embodied experience could affect higher-level motor cognition and perceptual body processing, thus pointing to a strict link between motor deficits, body schema alterations, and person processing difficulties.

Mothers' and fathers' early tactile contact behaviors during triadic and dyadic parent-infant interactions immediately after birth and at 3-months postpartum: Implications for early care behaviors and intervention.

Mothers' and fathers' touch were investigated during their first naturalistic interaction with their newborns, and maternal touch was predicted from newborn to 3-months postpartum during the Still-Face (SF) procedure. Both parents displayed more nurturing types of touch when interacting with their infants for the first time. Maternal touch at newborn predicted maternal touch after, but not before, the SF 3-months later; more touch after birth was associated with more soothing, regulating, types of maternal touch following the SF, suggesting that the nature of these interactive contexts (post-birth, post-SF) may be parallel. To our knowledge, this is the first study to investigate the full range of maternal and paternal touching behaviors during the first hour after birth. It is also one of the only investigations that considers how mothers' very first touch and physical contact relate to their later touch at 3-months. Our results uniquely contribute by revealing the nurturing and predictive quality of parents' touch, and underscore touch as a primary means of early contact and communication.

Exploring the EEG mu rhythm associated with observation and execution of a goal-directed action in 14-month-old preterm infants.

Electroencephalographic mu rhythm desynchronization is thought to reflect Mirror Neuron System (MNS) activity and represents an important neural correlate of the coupling between action execution and perception. It is still unclear if the MNS in human ontogeny is already available at the beginning of postnatal life and how early experience impacts its development. Premature birth provides a "natural condition" for investigating the effects of early, atypical extra-uterine experience on MNS. The main aim of the present study was to investigate whether the MNS activity is associated with prematurity. We compared the mu rhythm activity in preterm (PT) and full-term (FT) 14-month old infants during an action observation/execution (AO/AE) task. Mu rhythm desynchronization was computed over frontal, central, parietal and occipital regions. Both groups showed mu rhythm suppression in all the scalp regions during action execution. Different desynchronization patterns emerged during action observation. Specifically, FT infants showed mu suppression in the right frontal, bilateral parietal and occipital regions; whereas PT infants exhibited mu suppression only in the right parietal region. Overall, these preliminary findings indicate that an atypical extra uterine experience might have an impact on the MNS activity.

The dual nature of hypothalamic-pituitary-adrenal axis regulation in dyads of very preterm infants and their mothers.

The co-regulation of the hypothalamic-pituitary-adrenal (HPA) axis in mother-infant dyads is thought to be key for infant and child development. Nonetheless, previous literature presents some inconsistencies that might at least partially be due to the presence of risk conditions and the use of different statistical approaches to measure HPA axis co-regulation. Very preterm (VPT) birth represents one of these risk conditions as the early foundation of mother-infant interaction is disrupted. Both VPT infants and their mothers present evidence of altered HPA axis regulation. Nonetheless, the comparison of mother-infant HPA axis co-regulation in VPT infants compared to full-term (FT) ones has not been previously investigated. In this study, 3-month-old (corrected age) VPT infants and FT counterparts with their mothers took part in a well-validated stress-inducing laboratory task (i.e., double Face-to-Face Still-Face, FFSF paradigm). Salivary cortisol samples were obtained before (Baseline) and after (Early reactivity, Late reactivity and Recovery) the FFSF procedure. Dyadic HPA axis co-regulation was assessed at each sample time-point (i.e., in-moment coupling) as well as across samples (i.e., in-time synchrony). Significant in-moment coupling emerged at Baseline, Late reactivity and Recovery for FT infants' dyads only. An overlying pattern of salivary cortisol trajectories emerged between mothers and infants in the VPT group, whereas a more complex pattern of reciprocal and complementary co-regulation was found for FT infants' dyads. Although both groups gave evidence of HPA axis co-regulation, dyads of VPT infants appear to be less able to adapt reciprocally and dynamically to stressful conditions. These findings suggest that multiple approaches to account for dyadic HPA axis co-regulation should be used in order to depict the complex pattern of biological rhythms coordination in mother-infant dyads.

NICU Network Neurobehavioral Scale: 1-month normative data and variation from birth to 1 month.

BackgroundThe Neonatal Intensive Care Unit Network Neurobehavioral Scale (NNNS) is a standardized method for infant neurobehavioral assessment. Normative values are available for newborns, but the NNNS is not always feasible at birth. Unfortunately, 1-month NNNS normative data are lacking.AimsTo provide normative data for the NNNS examination at 1 month and to assess birth-to-one-month changes in NNNS summary scores.Study designThe NNNS was administered at birth and at 1 month within a longitudinal prospective study design.SubjectsA cohort of 99 clinically healthy full-term infants were recruited from a well-child nursery.Outcome measuresBirth-to-1-month NNNS variations were evaluated and the association of neonatal and sociodemographic variables with the rate of change of NNNS summary scores were investigated.Results and conclusionsNNNS scores from the 10th to the 90th percentile represent a range of normative performance at 1 month. A complex pattern of stability and change emerged comparing NNNS summary scores from birth to 1 month. Orienting, Regulation, and Quality of movements significantly increased, whereas Lethargy and Hypotonicity significantly decreased. Birth-to-1-month changes in NNNS performance suggest improvements in neurobehavioral organization. These data are useful for research purposes and for clinical evaluation of neurobehavioral performance in both healthy and at-risk 1-month-old infants.

The Face-to-Face Still-Face (FFSF) Paradigm in Clinical Settings: Socio-Emotional Regulation Assessment and Parental Support With Infants With Neurodevelopmental Disabilities.

Background: The Face-to-Face Still-Face (FFSF) paradigm is a well-acknowledged procedure to assess socio-emotional regulation in healthy and at-risk infants. Although it was developed mainly for research purposes, the FFSF paradigm has potential clinical implications for the assessment of socio-emotional regulation of infants with neurodevelopmental disabilities (ND) and to supporting parenting. Aim: The present paper describes the application of the FFSF paradigm as an evaluation and intervention tool in clinical practice with infants with ND and their parents. Methods: Theoretical and methodological insights for the use of the FFSF paradigm in the clinical setting are provided. Single-case vignettes from clinical practice further illustrate and provide exemplifications for the use of the FFSF with infants with ND and their parents. Results: From a clinical point of view, the use of the FFSF paradigm (1) offers a unique observational perspective on socio-emotional regulation in infants with ND and (2) enhances parents' sensitivity to their infants' behavior. Discussion: The FFSF paradigm appears to be a useful tool for clinical assessment of socio-emotional regulation in infants with ND and promote the quality of parenting and early parent-infant interaction.

Disentangling the Dyadic Dance: Theoretical, Methodological and Outcomes Systematic Review of Mother-Infant Dyadic Processes.

Background: During the last decades, the research on mother-infant dyad has produced a great amount of data, methods and theories, which largely contributed to set a revolution in the way we look at developmental changes during infancy and childhood. Very different constructs depict the different aspects of the "dyadic dance" occurring between a mother and her infant; nonetheless, a comprehensive and consistent systematization of these concepts in a coherent theoretical landscape is still lacking. Aim: In the present work, we aim at disentangling the different theoretical and methodological definitions of 9 dyadic constructs and we highlight their effects on infants' and children developmental outcomes. Methods: A literature search has been conducted on three databases-PubMed, Scopus, Web of Science. Three different reviews are reported here: (1) a review on the theoretical definitions of dyadic constructs; (2) a review of operational definitions, settings and methods of dyadic processes; (3) a systematic review of dyadic processes' outcomes for infants' and children developmental trajectories. Results: Two constructs emerged as wide meta-theoretical concepts (reciprocity and mutuality) and seven described specific processes (attunement, contingency, coordination, matching, mirroring, reparation, synchrony). A global model resuming the relationships among different processes is reported, which highlights the emergence of two specific cycles of dyadic functioning (i.e., matching-mismatching-reparation-synchrony; contingency, coordination, attunement, mirroring). A comprehensive review of the adopted measures is also provided. Finally, all the processes provided significant contributions to infants' behavioral, cognitive, and socio-emotional development during the first 3 years of age, but limited research has been conducted on specific processes (e.g. reparation and mirroring). Conclusion: The present study provides an original research-grounded framework to consider the different nature of mother-infant dyadic processes within a unified dyadic eco-system. Different levels of evidence emerged for the role of diverse mother-infant dyadic processes on infants' and children development. Open questions and future research directions are highlighted.

The BDNFval66met polymorphism and individual differences in temperament in 4-month-old infants: A pilot study.

Individual differences in infants' temperament are under genetic control. We investigated the association between brain-derived-neurotrophic-factor (BDNFval66met) polymorphism and temperament in 63 full-term infants. Met-carriers (N=25) had lower Regulatory capacities compared to val-homozygotes (N=38). These findings suggest that the BDNF polymorphism affects early temperament individual differences.

microRNAs differentially modulated in response to heat and drought stress in durum wheat cultivars with contrasting water use efficiency.

Plant stress response is a complex molecular process based on transcriptional and posttranscriptional regulation of many stress-related genes. microRNAs are the best-studied class of small RNAs known to play key regulatory roles in plant response to stress, besides being involved in plant development and organogenesis. We analyzed the leaf miRNAome of two durum wheat cultivars (Cappelli and Ofanto) characterized by a contrasting water use efficiency, exposed to heat stress, and mild and severe drought stress. On the whole, we identified 98 miRNA highly similar to previously known miRNAs and grouped in 47 MIR families, as well as 85 novel candidate miRNA, putatively wheat specific. A total of 80 known and novel miRNA precursors were found differentially expressed between the two cultivars or modulated by stress and many of them showed a cultivar-specific expression profile. Interestingly, most in silico predicted targets of the miRNAs coming from the differentially expressed precursors have been experimentally linked in other species to mechanisms controlling stomatal movement, a finding in agreement with previous results showing that Cappelli has a lower stomatal conductance than Ofanto. Selected miRNAs were validated through a standardized and reliable stem-loop qRT-PCR procedure.

Does quality of developmental care in NICUs affect health-related quality of life in 5-y-old children born preterm?

BACKGROUND: Preterm birth and Neonatal Intensive Care Unit (NICU) stay are early adverse experiences, which may affect health-related quality of life (HRQoL) even in the absence of prematurity-related morbidities. The aim of this multicenter longitudinal study was to examine the relation between quality levels of NICU Developmental Care (DC) and HRQoL at 60 mo in children who were born preterm. METHODS: HRQoL of 102 very preterm (VPT) children from 20 NICUs and 110 full-term controls was assessed using TNO-AZL Preschool Children's Quality of Life Questionnaire (TAPQOL). In VPT children, we compared HRQoL by splitting NICUs into units with high- and low-quality of DC according to the following two factors: (i) the infant centered care (ICC), and (ii) the infant pain management (IPM). RESULTS: Compared to VPT children from NICUs with high-quality of ICC, VPT children from NICUs with low-quality in ICC scored lower in HRQoL component which resulted from the aggregation of lively, positive emotionality, social and motor functioning. No differences were found between VPT children from high-quality ICC NICUs and full-term children and for the IPM index. CONCLUSION: Findings suggest that higher quality of DC in NICU related to ICC might mitigate long-term negative quality of life outcomes.

Pain-related stress in the Neonatal Intensive Care Unit and salivary cortisol reactivity to socio-emotional stress in 3-month-old very preterm infants.

Very preterm (VPT) infants are hospitalized in the Neonatal Intensive Care Unit (NICU) and exposed to varying levels of skin-breaking procedures (pain-related stress), even in absence of severe clinical conditions. Repeated and prolonged pain exposure may alter hypothalamic-pituitary-adrenal (HPA) axis reactivity in VPT infants. During the post-discharge period, altered HPA axis reactivity has been documented in response to non-social stressors, using salivary cortisol as a biomarker. However, little is known about the effects of NICU pain-related stress on subsequent HPA axis reactivity to socio-emotional stress in infants. We examined the relationship between pain-related stress in NICU and HPA axis reactivity (i.e., salivary cortisol reactivity) to an age-appropriate socio-emotional condition in 37 healthy VPT infants compared to 53 full-term (FT) controls. The number of skin-breaking procedures was obtained across NICU stay for VPT infants. At 3 months (corrected age for prematurity), all infants participated in the maternal Face-to-Face Still-Face (FFSF) procedure, in order to assess HPA axis reactivity to socio-emotional stress (i.e., maternal unresponsiveness). VPT infants exhibited a blunted salivary cortisol reactivity, which was associated with the amount of skin-breaking procedures during NICU: greater pain-related stress predicted lower salivary cortisol reactivity, adjusting for neonatal confounders. These findings further advance our knowledge of how early exposure to pain-related stress in NICU contributes to the programming of an altered HPA axis reactivity to socio-emotional stress in 3-month-old VPT infants, even in the absence of major perinatal complications.

Cytoplasmic genome substitution in wheat affects the nuclear-cytoplasmic cross-talk leading to transcript and metabolite alterations.

BACKGROUND: Alloplasmic lines provide a unique tool to study nuclear-cytoplasmic interactions. Three alloplasmic lines, with nuclear genomes from Triticum aestivum and harboring cytoplasm from Aegilops uniaristata, Aegilops tauschii and Hordeum chilense, were investigated by transcript and metabolite profiling to identify the effects of cytoplasmic substitution on nuclear-cytoplasmic signaling mechanisms. RESULTS: In combining the wheat nuclear genome with a cytoplasm of H. chilense, 540 genes were significantly altered, whereas 11 and 28 genes were significantly changed in the alloplasmic lines carrying the cytoplasm of Ae. uniaristata or Ae. tauschii, respectively. We identified the RNA maturation-related process as one of the most sensitive to a perturbation of the nuclear-cytoplasmic interaction. Several key components of the ROS chloroplast retrograde signaling, together with the up-regulation of the ROS scavenging system, showed that changes in the chloroplast genome have a direct impact on nuclear-cytoplasmic cross-talk. Remarkably, the H. chilense alloplasmic line down-regulated some genes involved in the determination of cytoplasmic male sterility without expressing the male sterility phenotype. Metabolic profiling showed a comparable response of the central metabolism of the alloplasmic and euplasmic lines to light, while exposing larger metabolite alterations in the H. chilense alloplasmic line as compared with the Aegilops lines, in agreement with the transcriptomic data. Several stress-related metabolites, remarkably raffinose, were altered in content in the H. chilense alloplasmic line when exposed to high light, while amino acids, as well as organic acids were significantly decreased. Alterations in the levels of transcript, related to raffinose, and the photorespiration-related metabolisms were associated with changes in the level of related metabolites. CONCLUSION: The replacement of a wheat cytoplasm with the cytoplasm of a related species affects the nuclear-cytoplasmic cross-talk leading to transcript and metabolite alterations. The extent of these modifications was limited in the alloplasmic lines with Aegilops cytoplasm, and more evident in the alloplasmic line with H. chilense cytoplasm. We consider that, this finding might be linked to the phylogenetic distance of the genomes.

A Survey of MicroRNA Length Variants Contributing to miRNome Complexity in Peach (Prunus Persica L.).

MicroRNAs (miRNAs) are short non-coding RNA molecules produced from hairpin structures and involved in gene expression regulation with major roles in plant development and stress response. Although each annotated miRNA in miRBase (www.mirbase.org) is a single defined sequence with no further details on possible variable sequence length, isomiRs - namely the population of variants of miRNAs coming from the same precursors - have been identified in several species and could represent a way of broadening the regulatory network of the cell. Next-gen-based sequencing makes it possible to comprehensively and accurately assess the entire miRNA repertoire including isomiRs. The aim of this work was to survey the complexity of the peach miRNome by carrying out Illumina high-throughput sequencing of miRNAs in three replicates of five biological samples arising from a set of different peach organs and/or phenological stages. Three hundred-ninety-two isomiRs (miRNA and miRNA*-related) corresponding to 26 putative miRNA coding loci, have been highlighted by mirDeep-P and analyzed. The presence of the same isomiRs in different biological replicates of a sample and in different tissues demonstrates that the generation of most of the detected isomiRs is not random. The degree of mature sequence heterogeneity is very different for each individual locus. Results obtained in the present work can thus contribute to a deeper view of the miRNome complexity and to better explore the mechanism of action of these tiny regulators.

On the complexity of miRNA-mediated regulation in plants: novel insights into the genomic organization of plant miRNAs.

MicroRNAs (miRNAs) are endogenous small non-coding RNAs of about 20-24 nt, known to play key roles in post-transcriptional gene regulation, that can be coded either by intergenic or intragenic loci. Intragenic (exonic and intronic) miRNAs can exert a role in the transcriptional regulation and RNA processing of their host gene. Moreover, the possibility that the biogenesis of exonic miRNAs could destabilize the corresponding protein-coding transcript and reduce protein synthesis makes their characterization very intriguing and suggests a possible novel mechanism of post-transcriptional regulation of gene expression. This work was designed to carry out the computational identification of putative exonic miRNAs in 30 plant species and the analysis of possible mechanisms involved in their regulation. The results obtained represent a useful starting point for future studies on the complex networks involved in microRNA-mediated gene regulation in plants.

Assessment of the relative toxicity of Cu2+ by measuring structural changes of supercoiled DNA.

A method for the measurement of the relative toxicity of Cu2+ in aquatic environments is proposed. It is based on the quantitative measurement on the shape change of the supercoiled DNA after it is contacted with different levels of Cu2+ for various time intervals. In the absence of any redox reagents, all supercoiled DNA degraded into other forms of DNA after 24h incubation in the presence of 5.13 x 10(-3), 5.08 x 10(-4) and 5.35 x 10(-5)mol/L Cu2+. At a lower Cu2+ concentration (10(-6)mol/L), 44% of supercoiled DNA retained its original supercoiled form after 24 h, and 29% after 48 h. The concentration of RC50, i.e. concentration of pollutants at which 50% of the supercoiled DNA was relaxed compared to control samples, can be obtained from the does-response curves at different exposure time, which may provide a rapid and convenient approach to assess the relative toxicity of environmental pollutants.