Prevalence of Low-Acuity Pediatric Emergency Medical Services Transports to a Pediatric Emergency Department in an Urban Area.

OBJECTIVES: Many patients transported by Emergency Medical Services (EMS) do not have emergent resource needs. Estimates for the proportion of pediatric EMS calls for low-acuity complaints, and thus potential candidates for alternative dispositions, vary widely and are often based on physician judgment. A more accurate reference standard should include patient assessments, interventions, and dispositions. The objective of this study was to describe the prevalence and characteristics of low-acuity pediatric EMS calls in an urban area. METHODS: This is a prospective observational study of children transported by EMS to a tertiary care pediatric emergency department. Patient acuity was defined using a novel composite measure that included physiologic assessments, resources used, and disposition. Bivariable and multivariable logistic regression were conducted to assess for factors associated with low-acuity status. RESULTS: A total of 996 patients were enrolled, of whom 32.9% (95% confidence interval, 30.0-36.0) were low acuity. Most of the sample was Black, non-Hispanic with a mean age of 7 years. When compared with adolescents, children younger than 1 year were more likely to be low acuity (adjusted odds ratio, 3.1 [1.9-5.1]). Patients in a motor vehicle crash were also more likely to be low acuity (adjusted odds ratio, 2.4 [1.2-4.6]). All other variables, including race, insurance status, chief complaint, and dispatch time, were not associated with low-acuity status. CONCLUSIONS: One third of pediatric patients transported to the pediatric emergency department by EMS in this urban area are for low-acuity complaints. Further research is needed to determine low-acuity rates in other jurisdictions and whether EMS providers can accurately identify low-acuity patients to develop alternative EMS disposition programs for children.

Rehydration Rates and Outcomes in Overweight Children With Diabetic Ketoacidosis.

BACKGROUND AND OBJECTIVES: The Pediatric Emergency Care Applied Research Network Fluid Therapies Under Investigation in Diabetic Ketoacidosis (DKA) (FLUID) Trial found that rapid fluid infusion does not increase the risk of cerebral injury. Concern persists, however, whether fluid rates should be adjusted for overweight or obese patients. We used the FLUID Trial database to evaluate associations between fluid infusion rate and outcomes in these patients. METHODS: We compared children and youth who were overweight, obese, or normal weight, in regard to protocol adherence, mental status changes, time to DKA resolution, and electrolyte abnormalities. We investigated associations between outcomes and the amount of fluid received in these groups. RESULTS: Obese children and youth were more likely to receive fluids at rates slower than dictated by protocol. Overweight and obese children and youth in the fast fluid arms, who received fluids per the study protocol based on their measured weight, had similar rates of mental status changes or clinically apparent cerebral injury as those with normal weights. Risk of hypophosphatemia was increased in those receiving larger initial bolus volumes and reduced in those receiving higher rehydration rates. No other metabolic outcomes were associated with rehydration. CONCLUSIONS: Protocol adherence data in the FLUID Trial suggest that physicians are uncomfortable using weight-based fluid calculations for overweight or obese children. However, higher rates of fluid infusion were not associated with increased risk of mental status changes or cerebral injury, suggesting that physicians should not limit fluid resuscitation in obese children and youth with DKA.

Clinical and Laboratory Predictors of Dehydration Severity in Children With Diabetic Ketoacidosis.

STUDY OBJECTIVE: Our primary objective was to characterize the degree of dehydration in children with diabetic ketoacidosis (DKA) and identify physical examination and biochemical factors associated with dehydration severity. Secondary objectives included describing relationships between dehydration severity and other clinical outcomes. METHODS: In this cohort study, we analyzed data from 753 children with 811 episodes of DKA in the Pediatric Emergency Care Applied Research Network Fluid Therapies Under Investigation Study, a randomized clinical trial of fluid resuscitation protocols for children with DKA. We used multivariable regression analyses to identify physical examination and biochemical factors associated with dehydration severity, and we described associations between dehydration severity and DKA outcomes. RESULTS: Mean dehydration was 5.7% (SD 3.6%). Mild (0 to <5%), moderate (5 to <10%), and severe (≥10%) dehydration were observed in 47% (N=379), 42% (N=343), and 11% (N=89) of episodes, respectively. In multivariable analyses, more severe dehydration was associated with new onset of diabetes, higher blood urea nitrogen, lower pH, higher anion gap, and diastolic hypertension. However, there was substantial overlap in these variables between dehydration groups. The mean length of hospital stay was longer for patients with moderate and severe dehydration, both in new onset and established diabetes. CONCLUSION: Most children with DKA have mild-to-moderate dehydration. Although biochemical measures were more closely associated with the severity of dehydration than clinical assessments, neither were sufficiently predictive to inform rehydration practice.

Transcription factor bHLH121 regulates root cortical aerenchyma formation in maize.

Root anatomical phenotypes present a promising yet underexploited avenue to deliver major improvements in yield and climate resilience of crops by improving water and nutrient uptake. For instance, the formation of root cortical aerenchyma (RCA) significantly increases soil exploration and resource capture by reducing the metabolic costs of root tissue. A key bottleneck in studying such phenotypes has been the lack of robust high-throughput anatomical phenotyping platforms. We exploited a phenotyping approach based on laser ablation tomography, termed Anatomics, to quantify variation in RCA formation of 436 diverse maize lines in the field. Results revealed a significant and heritable variation for RCA formation. Genome-wide association studies identified a single-nucleotide polymorphism mapping to a root cortex-expressed gene-encoding transcription factor bHLH121. Functional studies identified that the bHLH121 Mu transposon mutant line and CRISPR/Cas9 loss-of-function mutant line showed reduced RCA formation, whereas an overexpression line exhibited significantly greater RCA formation when compared to the wild-type line. Characterization of these lines under suboptimal water and nitrogen availability in multiple soil environments revealed that bHLH121 is required for RCA formation developmentally as well as under studied abiotic stress. Overall functional validation of the bHLH121 gene's importance in RCA formation provides a functional marker to select varieties with improved soil exploration and thus yield under suboptimal conditions.

Cognitive function following diabetic ketoacidosis in young children with type 1 diabetes.

INTRODUCTION: Young children with type 1 diabetes (T1D) may be at particularly high risk of cognitive decline following diabetic ketoacidosis (DKA). However, studies of cognitive functioning in T1D typically examine school-age children. The goal of this study was to examine whether a single experience of DKA is associated with lower cognitive functioning in young children. We found that recently diagnosed 3- to 5-year-olds who experienced one DKA episode, regardless of its severity, exhibited lower IQ scores than those with no DKA exposure. METHODS: We prospectively enrolled 46 3- to 5-year-old children, who presented with DKA at the onset of T1D, in a randomized multi-site clinical trial evaluating intravenous fluid protocols for DKA treatment. DKA was moderate/severe in 22 children and mild in 24 children. Neurocognitive function was assessed once 2-6 months after the DKA episode. A comparison group of 27 children with T1D, but no DKA exposure, was also assessed. Patient groups were matched for age and T1D duration at the time of neurocognitive testing. RESULTS: Children who experienced DKA, regardless of its severity, exhibited significantly lower IQ scores than children who did not experience DKA, F(2, 70) = 6.26, p = .003, partial η2  = .15. This effect persisted after accounting for socioeconomic status and ethnicity. CONCLUSIONS: A single DKA episode is associated with lower IQ scores soon after exposure to DKA in young children.

Intranasal fentanyl and discharge from the emergency department among children with sickle cell disease and vaso-occlusive pain: A multicenter pediatric emergency medicine perspective.

Children with sickle cell disease (SCD) commonly experience vaso-occlusive pain episodes (VOE) due to sickling of erythrocytes, which often requires care in the emergency department. Our objective was to assess the use and impact of intranasal fentanyl for the treatment of children with SCD-VOE on discharge from the emergency department in a multicenter study. We conducted a cross-sectional study at 20 academic pediatric emergency departments in the United States and Canada. We used logistic regression to test bivariable and multivariable associations between the outcome of discharge from the emergency department and candidate variables theoretically associated with discharge. The study included 400 patients; 215 (54%) were female. The median age was 14.6 (interquartile range 9.8, 17.6) years. Nineteen percent (n = 75) received intranasal fentanyl in the emergency department. Children who received intranasal fentanyl had nearly nine-fold greater adjusted odds of discharge from the emergency department compared to those who did not (adjusted odds ratio 8.99, 95% CI 2.81-30.56, p < .001). The rapid onset of action and ease of delivery without intravenous access offered by intranasal fentanyl make it a feasible initial parenteral analgesic in the treatment of children with SCD presenting with VOE in the acute-care setting. Further study is needed to determine potential causality of the association between intranasal fentanyl and discharge from the emergency department observed in this multicenter study.

Relationships among biochemical measures in children with diabetic ketoacidosis.

OBJECTIVES: Investigating empirical relationships among laboratory measures in children with diabetic ketoacidosis (DKA) can provide insights into physiological alterations occurring during DKA. We determined whether alterations in laboratory measures during DKA conform to theoretical predictions. METHODS: We used Pearson correlation statistics and linear regression to investigate correlations between blood glucose, electrolytes, pH and PCO2 at emergency department presentation in 1,681 pediatric DKA episodes. Among children with repeat DKA episodes, we also assessed correlations between laboratory measures at the first vs. second episode. RESULTS: pH and bicarbonate levels were strongly correlated (r=0.64), however, pH and PCO2 were only loosely correlated (r=0.17). Glucose levels were correlated with indicators of dehydration and kidney function (blood urea nitrogen (BUN), r=0.44; creatinine, r=0.42; glucose-corrected sodium, r=0.32). Among children with repeat DKA episodes, PCO2 levels tended to be similar at the first vs. second episode (r=0.34), although pH levels were only loosely correlated (r=0.19). CONCLUSIONS: Elevated glucose levels at DKA presentation largely reflect alterations in glomerular filtration rate. pH and PCO2 are weakly correlated suggesting that respiratory responses to acidosis vary among individuals and may be influenced by pulmonary and central nervous system effects of DKA.

Genome wide association analysis of root hair traits in rice reveals novel genomic regions controlling epidermal cell differentiation.

BACKGROUND: Genome wide association (GWA) studies demonstrate linkages between genetic variants and traits of interest. Here, we tested associations between single nucleotide polymorphisms (SNPs) in rice (Oryza sativa) and two root hair traits, root hair length (RHL) and root hair density (RHD). Root hairs are outgrowths of single cells on the root epidermis that aid in nutrient and water acquisition and have also served as a model system to study cell differentiation and tip growth. Using lines from the Rice Diversity Panel-1, we explored the diversity of root hair length and density across four subpopulations of rice (aus, indica, temperate japonica, and tropical japonica). GWA analysis was completed using the high-density rice array (HDRA) and the rice reference panel (RICE-RP) SNP sets. RESULTS: We identified 18 genomic regions related to root hair traits, 14 of which related to RHD and four to RHL. No genomic regions were significantly associated with both traits. Two regions overlapped with previously identified quantitative trait loci (QTL) associated with root hair density in rice. We identified candidate genes in these regions and present those with previously published expression data relevant to root hair development. We re-phenotyped a subset of lines with extreme RHD phenotypes and found that the variation in RHD was due to differences in cell differentiation, not cell size, indicating genes in an associated genomic region may influence root hair cell fate. The candidate genes that we identified showed little overlap with previously characterized genes in rice and Arabidopsis. CONCLUSIONS: Root hair length and density are quantitative traits with complex and independent genetic control in rice. The genomic regions described here could be used as the basis for QTL development and further analysis of the genetic control of root hair length and density. We present a list of candidate genes involved in root hair formation and growth in rice, many of which have not been previously identified as having a relation to root hair growth. Since little is known about root hair growth in grasses, these provide a guide for further research and crop improvement.

2022 Systematic Review of Evidence-Based Guidelines for Prehospital Care.

INTRODUCTION: Multiple national organizations and federal agencies have promoted the development, implementation, and evaluation of evidence-based guidelines (EBGs) for prehospital care. Previous efforts have identified opportunities to improve the quality of prehospital guidelines and highlighted the value of high-quality EBGs to inform initial certification and continued competency activities for EMS personnel. OBJECTIVES: We aimed to perform a systematic review of prehospital guidelines published from January 2018 to April 2021, evaluate guideline quality, and identify top-scoring guidelines to facilitate dissemination and educational activities for EMS personnel. METHODS: We searched the literature in Ovid Medline and EMBASE from January 2018 to April 2021, excluding guidelines identified in a prior systematic review. Publications were retained if they were relevant to prehospital care, based on organized reviews of the literature, and focused on providing recommendations for clinical care or operations. Included guidelines were appraised to identify if they met the National Academy of Medicine (NAM) criteria for high-quality guidelines and scored across the six domains of the Appraisal of Guidelines for Research and Evaluation (AGREE) II tool. RESULTS: We identified 75 guidelines addressing a variety of clinical and operational aspects of EMS medicine. About half (n = 39, 52%) addressed time/life-critical conditions and 33 (44%) contained recommendations relevant to non-clinical/operational topics. Fewer than half (n = 35, 47%) were based on systematic reviews of the literature. Nearly one-third (n = 24, 32%) met all NAM criteria for clinical practice guidelines. Only 27 (38%) guidelines scored an average of >75% across AGREE II domains, with content relevant to guideline implementation most commonly missing. CONCLUSIONS: This interval systematic review of prehospital EBGs identified many new guidelines relevant to prehospital care; more than all guidelines reported in a prior systematic review. Our review reveals important gaps in the quality of guideline development and the content in their publications, evidenced by the low proportion of guidelines meeting NAM criteria and the scores across AGREE II domains. Efforts to increase guideline dissemination, implementation, and related education may be best focused around the highest quality guidelines identified in this review.

Recommendations for Improving the Quality of Prehospital Evidence-Based Guidelines.

Evidence-based guidelines that provide recommendations for clinical care or operations are increasingly being published to inform the EMS community. The quality of evidence evaluation and methodological rigor undertaken to develop and publish these recommendations vary. This can negatively affect dissemination, education, and implementation efforts. Guideline developers and end users could be better informed by efforts across medical specialties to improve the quality of guidelines, including the use of specific criteria that have been identified within the highest quality guidelines. In this special contribution, we aim to describe the current state of published guidelines available to the EMS community informed by two recent systematic reviews of existing prehospital evidenced based guidelines (EBGs). We further aim to provide a description of key elements of EBGs, methods that can be used to assess their quality, and concrete recommendations for guideline developers to improve the quality of evidence evaluation, guideline development, and reporting. Finally, we outline six key recommendations for improving prehospital EBGs, informed by systematic reviews of prehospital guidelines performed by the Prehospital Guidelines Consortium.

Clinician and Caregiver Determinations of Acuity for Children Transported by Emergency Medical Services: A Prospective Observational Study.

STUDY OBJECTIVE: Many Emergency Medical Services (EMS) agencies have developed alternative disposition processes for patients with nonemergency problems, but there is a lack of evidence demonstrating EMS clinicians can accurately determine acuity in pediatric patients. Our study objective was to determine EMS and other stakeholders' ability to identify low acuity pediatric EMS patients. METHODS: We conducted a prospective, observational study of children transported to a pediatric emergency department (ED) by EMS. Acuity was defined using a composite measure that included data from the patient's vital signs and examination, resources used (laboratory results, radiographs, etc), and disposition. For each patient, an EMS clinician, patient caregiver, ED nurse, and ED provider completed a survey as soon as possible after the patient's arrival at the ED. The survey asked respondents 2 questions: to state their level of agreement that a patient was low acuity and could the patient have been managed by various alternative dispositions. For each respondent group, we calculated the sensitivity, specificity, and positive and negative predictive values for low acuity versus the composite measure. RESULTS: From August 2020 through September 2021, we approached 1,015 caregivers, of whom 996 (99.8%) agreed to participate and completed the survey. Survey completion varied between 78.7% and 84.1% for EMS and ED nurses and providers. The mean patient age was 7 years, 62.6% were non-Hispanic Black, and 60% were enrolled in public insurance programs. Of the 996 patient encounters, 33% were determined to be low acuity by the composite measure. The positive predictive value for EMS clinicians when identifying low acuity children was 0.60 (95% confidence intervals [CI], 0.58 to 0.67). The positive predictive value for ED nurses and providers was 0.67 (95% CI, 0.61 to 0.72) and 0.68 (95% CI, 0.63 to 0.74) respectively. The negative predictive value for EMS clinicians when identifying not low acuity children was 0.62 (95% CI, 0.58 to 0.67). The negative predictive value for ED nurses and providers was 0.72 (95% CI, 0.68 to 0.76) and 0.73 (95% CI, 0.70 to 0.77) respectively. Caregivers had the lowest positive predictive value 0.34 (95% CI, 0.30 to 0.40) but the highest negative predictive value 0.82 (95% CI, 0.79 to 0.85). The EMS clinicians, ED nurses and providers were more likely than caregivers to think that a child with a low acuity complaint could have been safely managed by alternative disposition. CONCLUSION: All 4 groups studied had a limited ability to identify which children transported by EMS would have no emergency resource needs, and support for alternative disposition was limited. For children to be included in alternative disposition processes, novel triage tools, training, and oversight will be required to prevent undertriage.

Emergency Medical Services Clinicians' Perspectives on Pediatric Non-Transport.

OBJECTIVES: Emergency medical services clinicians do not transport one-third of all children assessed, even without official pediatric non-transport protocols. Little is known about how EMS clinicians and caregivers decide not to transport a child. Our objectives were to describe how EMS clinicians currently decide whether or not to transport a child and identify barriers to and enablers of successfully implementing an EMS clinician-initiated pediatric non-transport protocol. METHODS: We conducted six virtual focus groups with EMS clinicians from the mid-Atlantic. A PhD trained facilitator moderated all groups using a semi-structured moderator guide. Multiple investigators independently coded a deidentified sample transcript. One team member then completed axial coding of the remaining transcripts. Thematic saturation was achieved. Clusters of similar codes were grouped into themes by consensus. RESULTS: We recruited 50 participants, of whom 70% were paramedics and 28% emergency medical technicians. There was agreement that caregivers often use 9-1-1 for low acuity complaints. Participants stated that non-transport usually occurs after shared decision-making between EMS clinicians and caregivers; EMS clinicians advise whether transport is necessary, but caregivers are responsible for making the final decision and signing refusal documentation. Subthemes for how non-transport decisions were made included the presence of agency protocols, caregiver preferences, absence of a guardian on the scene, EMS clinician variability, and distance to the nearest ED. Participants identified the following features that would enable successful implementation of an EMS clinician-initiated non-transport process: a user-friendly interface, clear protocol endpoints, the inclusion of vital sign parameters, resources to leave with caregivers, and optional direct medical oversight. CONCLUSIONS: EMS clinicians in our study agreed that non-transport is currently a caregiver decision, but noted a collaborative process of shared decision-making where EMS clinicians advise caregivers whether transport is indicated. Further research is needed to understand the safety of this practice. This study suggests there may be a need for EMS-initiated alternative disposition/non-transport protocols.

Pyuria in Children with Diabetic Ketoacidosis.

Acute kidney injury occurs frequently during pediatric diabetic ketoacidosis (DKA). We reviewed urinalyses from 561 children with DKA; pyuria was detected in 19% overall and in 40% of children with more comprehensive urine testing (≥3 urinalyses) during DKA.

Response of Southeast Asian rice root architecture and anatomy phenotypes to drought stress.

Drought stress in Southeast Asia greatly affects rice production, and the rice root system plays a substantial role in avoiding drought stress. In this study, we examined the phenotypic and genetic correlations among root anatomical, morphological, and agronomic phenotypes over multiple field seasons. A set of >200 rice accessions from Southeast Asia (a subset of the 3000 Rice Genomes Project) was characterized with the aim to identify root morphological and anatomical phenotypes related to productivity under drought stress. Drought stress resulted in slight increases in the basal metaxylem and stele diameter of nodal roots. Although few direct correlations between root phenotypes and grain yield were identified, biomass was consistently positively correlated with crown root number and negatively correlated with stele diameter. The accessions with highest grain yield were characterized by higher crown root numbers and median metaxylem diameter and smaller stele diameter. Genome-wide association study (GWAS) revealed 162 and 210 significant SNPs associated with root phenotypes in the two seasons which resulted in identification of 59 candidate genes related to root development. The gene OsRSL3 was found in a QTL region for median metaxylem diameter. Four SNPs in OsRSL3 were found that caused amino acid changes and significantly associated with the root phenotype. Based on the haplotype analysis for median metaxylem diameter, the rice accessions studied were classified into five allele combinations in order to identify the most favorable haplotypes. The candidate genes and favorable haplotypes provide information useful for the genetic improvement of root phenotypes under drought stress.

Many paths to one goal: Identifying integrated rice root phenotypes for diverse drought environments.

Drought is a major source of yield loss in the production of rice (Oryza sativa L.), and cultivars that maintain yield under drought across environments and drought stress scenarios are urgently needed. Root phenotypes directly affect water interception and uptake, so plants with root systems optimized for water uptake under drought would likely exhibit reduced yield loss. Deeper nodal roots that have a low metabolic cost per length (i.e., cheaper roots) via smaller root diameter and/or more aerenchyma and that transport water efficiently through smaller diameter metaxylem vessels may be beneficial during drought. Subsets of the Rice Diversity Panel 1 and Azucena × IR64 recombinant inbred lines were grown in two greenhouse and two rainout shelter experiments under drought stress to assess their shoot, root anatomical, and root architectural phenotypes. Root traits and root trait plasticity in response to drought varied with genotype and environment. The best-performing groups in the rainout shelter experiments had less plasticity of living tissue area in nodal roots than the worst performing groups. Root traits under drought were partitioned into similar groups or clusters via the partitioning-around-medoids algorithm, and this revealed two favorable integrated root phenotypes common within and across environments. One favorable integrated phenotype exhibited many, deep nodal roots with larger root cross-sectional area and more aerenchyma, while the other favorable phenotype exhibited many, deep nodal roots with small root cross-sectional area and small metaxylem vessels. Deeper roots with high theoretical axial hydraulic conductance combined with reduced root metabolic cost contributed to greater shoot biomass under drought. These results reflect how some root anatomical and architectural phenes work in concert as integrated phenotypes to influence the performance of plant under drought stress. Multiple integrated root phenotypes are therefore recommended to be selected in breeding programs for improving rice yield across diverse environments and drought scenarios.

Clinical Characteristics of Children with Cerebral Injury preceding Treatment of Diabetic Ketoacidosis.

Previous studies have identified more severe acidosis and higher blood urea nitrogen (BUN) as risk factors for cerebral injury during treatment of diabetic ketoacidosis (DKA) in children; however, cerebral injury also can occur before DKA treatment. We found that lower pH and higher BUN levels also were associated with cerebral injury at presentation.

Identifying pediatric patients with multisystem inflammatory syndrome in children presenting to a pediatric emergency department.

OBJECTIVE: To compare clinical and laboratory features of children with Multisystem Inflammatory Syndrome in Children (MIS-C) to those evaluated for MIS-C in the Emergency Department (ED). METHODS: We conducted a retrospective review of the medical record of encounters with testing for inflammatory markers in an urban, tertiary care Pediatric ED from March 1, 2020 to July 31, 2020. We abstracted demographic information, laboratory values, selected medications and diagnoses. We reviewed the record for clinical presentation for the subset of patients admitted to the hospital for suspected MIS-C. We then used receiver operating curves and logistic regression to evaluate the utility of candidate laboratory values to predict MIS-C status. RESULTS: We identified 32 patients with confirmed MIS-C and 15 admitted and evaluated for MIS-C but without confirmation of SARS CoV-2 infection. We compared these patients to 267 encounters with screening laboratories for MIS-C. Confirmed MIS-C patients had an older median age, higher median fever on presentation and were predominantly of Hispanic and non-Hispanic Black race/ethnicity. All children with MIS-C had a C-reactive protein (CRP) >4.5 mg/dL, were more likely to have Brain Natriuretic Peptide >400 pg/mL (OR 10.50, 95%CI 4.40-25.04), D-Dimer >3 µg/mL (7.51, [3.18-17.73]), and absolute lymphocyte count (ALC) <1.5 K/mcL (21.42, [7.19-63.76]). We found CRP >4.5 mg/dL and ALC <1.5 K/mcL to be 86% sensitive and 91% specific to identify MIS-C among patients screened in our population. CONCLUSIONS: We identified that elevated CRP and lymphopenia was 86% sensitive and 91% specific for identification of children with MIS-C.

Soil penetration by maize roots is negatively related to ethylene-induced thickening.

Radial expansion is a classic response of roots to a mechanical impedance that has generally been assumed to aid penetration. We analysed the response of maize nodal roots to impedance to test the hypothesis that radial expansion is not related to the ability of roots to cross a compacted soil layer. Genotypes varied in their ability to cross the compacted layer, and those with a steeper approach to the compacted layer or less radial expansion in the compacted layer were more likely to cross the layer and achieve greater depth. Root radial expansion was due to cortical cell size expansion, while cortical cell file number remained constant. Genotypes and nodal root classes that exhibited radial expansion in the compacted soil layer generally also thickened in response to exogenous ethylene in hydroponic culture, that is, radial expansion in response to ethylene was correlated with the thickening response to impedance in soil. We propose that ethylene insensitive roots, that is, those that do not thicken and can overcome impedance, have a competitive advantage under mechanically impeded conditions as they can maintain their elongation rates. We suggest that prolonged exposure to ethylene could function as a stop signal for axial root growth.

Root angle in maize influences nitrogen capture and is regulated by calcineurin B-like protein (CBL)-interacting serine/threonine-protein kinase 15 (ZmCIPK15).

Crops with reduced nutrient and water requirements are urgently needed in global agriculture. Root growth angle plays an important role in nutrient and water acquisition. A maize diversity panel of 481 genotypes was screened for variation in root angle employing a high-throughput field phenotyping platform. Genome-wide association mapping identified several single nucleotide polymorphisms (SNPs) associated with root angle, including one located in the root expressed CBL-interacting serine/threonine-protein kinase 15 (ZmCIPK15) gene (LOC100285495). Reverse genetic studies validated the functional importance of ZmCIPK15, causing a approximately 10° change in root angle in specific nodal positions. A steeper root growth angle improved nitrogen capture in silico and in the field. OpenSimRoot simulations predicted at 40 days of growth that this change in angle would improve nitrogen uptake by 11% and plant biomass by 4% in low nitrogen conditions. In field studies under suboptimal N availability, the cipk15 mutant with steeper growth angles had 18% greater shoot biomass and 29% greater shoot nitrogen accumulation compared to the wild type after 70 days of growth. We propose that a steeper root growth angle modulated by ZmCIPK15 will facilitate efforts to develop new crop varieties with optimal root architecture for improved performance under edaphic stress.