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.

Three-dimensional imaging reveals that positions of cyst nematode feeding sites relative to xylem vessels differ between susceptible and resistant wheat.

KEY MESSAGE: Resistance conferred by the Cre8 locus of wheat prevents cereal cyst nematode feeding sites from reaching and invading root metaxylem vessels. Cyst nematodes develop syncytial feeding sites within plant roots. The success of these sites is affected by host plant resistance. In wheat (Triticum aestivum L.), 'Cre' loci affect resistance against the cereal cyst nematode (CCN) Heterodera avenae. To investigate how one of these loci (Cre8, on chromosome 6B) confers resistance, CCN-infected root tissue from susceptible (-Cre8) and resistant (+Cre8) wheat plants was examined using confocal microscopy and laser ablation tomography. Confocal analysis of transverse sections showed that feeding sites in the roots of -Cre8 plants were always adjacent to metaxylem vessels, contained many intricate 'web-like' cell walls, and sometimes 'invaded' metaxylem vessels. In contrast, feeding sites in the roots of +Cre8 plants were usually not directly adjacent to metaxylem vessels, had few inner cell walls and did not 'invade' metaxylem vessels. Models based on data from laser ablation tomography confirmed these observations. Confocal analysis of longitudinal sections revealed that CCN-induced xylem modification that had previously been reported for susceptible (-Cre8) wheat plants is less extreme in resistant (+Cre8) plants. Application of a lignin-specific stain revealed that secondary thickening around xylem vessels in CCN-infected roots was greater in +Cre8 plants than in -Cre8 plants. Collectively, these results indicate that Cre8 resistance in wheat acts by preventing cyst nematode feeding sites from reaching and invading root metaxylem vessels.

Plant roots sense soil compaction through restricted ethylene diffusion.

Soil compaction represents a major challenge for modern agriculture. Compaction is intuitively thought to reduce root growth by limiting the ability of roots to penetrate harder soils. We report that root growth in compacted soil is instead actively suppressed by the volatile hormone ethylene. We found that mutant Arabidopsis and rice roots that were insensitive to ethylene penetrated compacted soil more effectively than did wild-type roots. Our results indicate that soil compaction lowers gas diffusion through a reduction in air-filled pores, thereby causing ethylene to accumulate in root tissues and trigger hormone responses that restrict growth. We propose that ethylene acts as an early warning signal for roots to avoid compacted soils, which would be relevant to research into the breeding of crops resilient to soil compaction.

Laser ablation tomography for visualization of root colonization by edaphic organisms.

Soil biota have important effects on crop productivity, but can be difficult to study in situ. Laser ablation tomography (LAT) is a novel method that allows for rapid, three-dimensional quantitative and qualitative analysis of root anatomy, providing new opportunities to investigate interactions between roots and edaphic organisms. LAT was used for analysis of maize roots colonized by arbuscular mycorrhizal fungi, maize roots herbivorized by western corn rootworm, barley roots parasitized by cereal cyst nematode, and common bean roots damaged by Fusarium. UV excitation of root tissues affected by edaphic organisms resulted in differential autofluorescence emission, facilitating the classification of tissues and anatomical features. Samples were spatially resolved in three dimensions, enabling quantification of the volume and distribution of fungal colonization, western corn rootworm damage, nematode feeding sites, tissue compromised by Fusarium, and as well as root anatomical phenotypes. Owing to its capability for high-throughput sample imaging, LAT serves as an excellent tool to conduct large, quantitative screens to characterize genetic control of root anatomy and interactions with edaphic organisms. Additionally, this technology improves interpretation of root-organism interactions in relatively large, opaque root segments, providing opportunities for novel research investigating the effects of root anatomical phenes on associations with edaphic organisms.

Magnetic resonance imaging versus ultrasound in diagnosis of distal biceps tendon avulsion.

INTRODUCTION: The severity of distal biceps tendon (DBT) injuries ranges from partial to complete tears leading to various clinical manifestation. Accuracy of early diagnosis and selection of treatment are critical to long-term recovery outcomes. Magnetic resonance imaging (MRI) or ultrasonography (US) are two commonly modalities for pre-operative diagnosis. The objective of this study was to determine the efficiency of MRI and ultrasonography US in the diagnosis of DBT rupture confirmed by operative findings. HYPOTHESIS: MRI and US are equally effective in terms of accuracy, sensitivity and specificity. MATERIAL AND METHODS: A total of 31 patients with DBT avulsion and surgical treatment were recruited for this retrospective study. All these patients received both US and MRI examinations prior to surgery. DBT avulsion was classified into partial tear and complete tear. Diagnosis outcomes by MRI and US were analyzed and compared statistically for the accuracy, sensitivity, and specificity in discriminating partial and complete DBT tears. RESULTS: The accuracy of MRI and US was 86.4% and 45.5% in diagnosis of complete DBT rupture, respectively. Accuracy rate of MRI (66.7%) was the same as US in diagnosis of partial tear. Overall accuracy rate of MRI (80.6%) was higher than US (51.6%) in diagnosis all DBT avulsion with an odds ratio of 3.9. Sensitivity and specificity of MRI were 76.0% and 50.0%, while that of ultrasonography were 62.5% and 20.0%. CONCLUSIONS: The findings of this study suggest that MRI is a more accurate imaging modality at correctly identifying the type of DBT tear although US is more cost-effective. LEVEL OF EVIDENCE: III, Cohort study, Diagnosis study.

Clinical Characteristics and Long-term Outcomes After Septic Arthritis of the Native Glenohumeral Joint: A 20-Year Retrospective Review.

Septic arthritis of the native glenohumeral joint is rare, and there is little information available regarding the natural progression and long-term joint outcomes of this pathology. The authors performed a retrospective analysis of 97 patients with culture-positive glenohumeral septic arthritis between 1995 and 2015 at their institution with a mean clinical follow-up of 83.1 months. Patient records were reviewed to document demographic and laboratory data, clinical presentation, postoperative complications, recurrences, and subsequent shoulder arthroplasty. Common comorbidities uncovered included 20 immunocompromised patients (20.6%), intravenous drug use among 27 patients (27.8%), diabetes mellitus among 40 patients (41.2%), and 18 patients (18.5%) receiving hemodialysis. Staphylococcus aureus was the most common pathogen identified (61 patients; 62.8%), followed by streptococcal species (17 patients; 17.2%). Hematogenous spread of infection was the most common etiology of shoulder sepsis (40.2%). Seven patients (7.2%) developed shoulder sepsis of undetermined etiology in the absence of established risk factors, and 16 patients (16.4%) developed recurrent glenohumeral septic arthritis at a mean of 40 months following initial eradication of infection. Three patients (3.0%) eventually underwent same-side shoulder arthroplasty at a mean of 18 months following septic arthritis, with none experiencing a periprosthetic joint infection. Glenohumeral septic arthritis is highly unlikely in the absence of medical risk factors. Long-term recurrence after clinically successful treatment is low (16.5%), and few patients undergo elective arthroplasty following shoulder septic arthritis. However, orthopedic surgeons can expect 30% to 40% of patients to require multiple trips to the operating room to successfully treat the initial joint infection, regardless of treatment method. [Orthopedics. 2019; 42(1):e118-e123.].

Adductor Canal Block Versus Femoral Nerve Block for Pain Control After Anterior Cruciate Ligament Reconstruction: A Prospective Randomized Trial.

BACKGROUND: Femoral nerve block (FNB) is a commonly performed technique that has been proven to provide effective regional analgesia after anterior cruciate ligament (ACL) reconstruction. The adductor canal block (ACB) uses a similar sensory block around the knee while avoiding motor blockade of the quadriceps muscles. PURPOSE/HYPOTHESIS: The purpose of our study was to compare the efficacy of FNB versus ACB for pain control after ACL reconstruction. It was hypothesized that there would be no difference in pain levels or opioid requirements between the 2 groups. STUDY DESIGN: Randomized controlled trial; Level of evidence, 1. METHODS: We performed a prospective, double-blinded, randomized controlled trial. Sixty patients undergoing primary ACL reconstruction with bone-patellar tendon-bone autograft were randomized to receive either an ACB or an FNB preoperatively. The primary outcomes assessed were pain levels (visual analog scale) and narcotic requirements for 4 days after surgery. Secondary outcomes included ability to perform a straight leg raise in the recovery room and difference in thigh circumference between the operative and nonoperative leg measured at 7 days postoperatively. RESULTS: Morphine requirements were less in the ACB group in the first 4 hours postoperatively ( P = .02). Aside from this time interval, no differences were found between the 2 groups with regard to opioid requirements and pain scores at any other time. Similarly, no differences were noted in patients' ability to perform a straight leg raise in the recovery room ( P = .13) or in thigh circumference at the first postoperative visit ( P = .09). CONCLUSION: The results of our study suggest similar efficacy in perioperative pain control with the use of an ACB for ACL reconstruction when compared with FNB. The potential long-term benefit of quadriceps preservation with the ACB is worthy of future study. REGISTRATION: NCT03033589 (ClinicalTrials.gov identifier).

Ethylene modulates root cortical senescence in barley.

Background and Aims: Root cortical senescence (RCS) is a poorly understood phenomenon with implications for adaptation to edaphic stress. It was hypothesized that RCS in barley (Hordeum vulgare L.) is (1) accelerated by exogenous ethylene exposure; (2) accompanied by differential expression of ethylene synthesis and signalling genes; and (3) associated with differential expression of programmed cell death (PCD) genes. Methods: Gene expression of root segments from four barley genotypes with and without RCS was evaluated using quantitative real-time PCR (qRT-PCR). The progression of RCS was manipulated with root zone ethylene and ethylene inhibitor applications. Key Results: The results demonstrate that ethylene modulates RCS. Four genes related to ethylene synthesis and signalling were upregulated during RCS in optimal, low nitrogen and low phosphorus nutrient regimes. RCS was accelerated by root zone ethylene treatment, and this effect was reversed by an ethylene action inhibitor. Roots treated with exogenous ethylene had 35 and 46 % more cortical senescence compared with the control aeration treatment in seminal and nodal roots, respectively. RCS was correlated with expression of two genes related to programmed cell death (PCD). Conclusions: The development of RCS is similar to root cortical aerenchyma formation with respect to ethylene modulation of the PCD process.

Intraocular Pressure Increases After Intraarticular Knee Injection With Triamcinolone but Not Hyaluronic Acid.

BACKGROUND: Intraarticular steroid injections are a common first-line therapy for severe osteoarthritis, which affects an estimated 27 million people in the United States. Although topical, oral, intranasal, and inhalational steroids are known to increase intraocular pressure in some patients, the effect of intraarticular steroid injections on intraocular pressure has not been investigated, to the best of our knowledge. If elevated intraocular pressure is sustained for long periods of time or is of sufficient magnitude acutely, permanent loss of the visual field can occur. QUESTIONS/PURPOSES: How does intraocular pressure change 1 week after an intraarticular knee injection either with triamcinolone acetonide or hyaluronic acid? METHODS: A nonrandomized, nonblinded prospective cohort study was conducted at an outpatient, ambulatory orthopaedic clinic. This study compared intraocular pressure elevation before and 1 week after intraarticular knee injection of triamcinolone acetonide versus hyaluronic acid for management of primary osteoarthritis of the knee. Patients self-selected to be injected in their knee with either triamcinolone acetonide or hyaluronic acid before being informed of the study. The primary endpoint was intraocular pressure elevation of ≥ 7 mm Hg 1 week after injection. This cutoff is determined as the minimum significant pressure change in the ophthalmology literature recognized as an intermediate responder to steroids. Intraocular pressure was measured using a handheld Tono-Pen® applanation device. This device is frequently used in intraocular pressure measurement in clinical and research settings; 10 sequential measurements are obtained and averaged with a confidence interval. Only measurements with a 95% confidence interval were used. Over a 6-month period, a total of 96 patients were approached to enroll in the study. Sixty-two patients out of 96 approached (65%) agreed. Thirty-one (50%) were injected with triamcinolone and 31 (50%) were injected with hyaluronic acid. Patients with osteoarthritis of the knee who were suitable candidates for either a steroid injection or hyaluronic acid injection were included in the study. Exclusion criteria included previous glaucoma surgery, previous corneal injury precluding use of a Tono-Pen, current acute or chronic steroid use, and diagnosis of glaucoma other than primary open-angle. Patients with elevated intraocular pressure at the 1-week timepoint were invited to return at 1 month for repeat measurement; however, only five of nine (55.6%) were able to do so. The mean age of the total population was 64.1 ± 11.65 years. There were 46 (74%) women and 16 men. Patient in the hyaluronic acid injection group were younger than the triamcinolone group, 59.5 ± 11.7 versus 68.7 ± 9.7 years of age (p < 0.003). RESULTS: The mean intraocular pressure increased by 2.79 mm Hg 1 week after treatment with triamcinolone, but it did not change among those patients treated with hyaluronic acid (2.79 ± 9.9 mm Hg versus -0.14 ± 2.96 mm Hg; mean difference 2.93 mm Hg; 95% confidence interval, -0.71 to 6.57 mm Hg; p = 0.12). More patients who received triamcinolone injections developed an increase in intraocular pressure > 7 mm than did those who received hyaluronic acid (29% [nine of 29] versus 0% [zero of 31]; p = 0.002). Of the nine patients who developed elevated intraocular pressure after a triamcinolone injection, five returned for reevaluation 1 month later, and four of them had pressures that remained elevated > 7 mm Hg from baseline. CONCLUSIONS: There appears to be an associated intraocular pressure elevation found in patients who have undergone a triamcinolone injection of the knee. Further larger scale randomized investigations are warranted to determine the longevity of this pressure elevation as well as long-term clinical implications, including optic nerve damage and visual field loss. LEVEL OF EVIDENCE: Level II, therapeutic study.

Liposomal bupivacaine versus interscalene nerve block for pain control after shoulder arthroplasty: a prospective randomized trial.

HYPOTHESIS: Our hypothesis was that in patients undergoing shoulder arthroplasty, a prospective randomized trial would find no significant differences in average daily pain scores of those treated with interscalene nerve block (INB) vs. local liposomal bupivacaine (LB). METHODS: Sixty patients undergoing primary shoulder arthroplasty were assessed for eligibility. Study arms included either intraoperative local infiltration of LB (20 mL bupivacaine/20 mL saline) or preoperative INB, with a primary outcome of postoperative average daily visual analog scale scores for 4 days. Secondary outcomes assessed included opioid consumption, length of stay, and complications. Randomization was by a computerized algorithm. Only the observer was blinded to the intervention. RESULTS: Three patients were excluded, all before randomization. A total of 57 patients were analyzed. Outcomes showed a significant increase in pain in the LB group between 0 and 8 hours postoperatively (mean [standard deviation] 5.3 [2.2] vs. 2.5 [3.0]; P = .001). A significant increase in intravenous morphine equivalents was found in the INB group at 13 to 16 hours (mean [standard deviation] 1.2 [0.9] vs. 0.6 [0.7]; P = .01). No significant differences were found in any variable after postoperative day 0 between the 2 groups. CONCLUSION: An increase in early postoperative pain on the day of surgery was found with LB, whereas the INB group required more narcotics at the end of the day. After the day of surgery, there were no significant differences found in any variables. These findings suggest that LB provides similar overall pain relief as INB, with no increase in complications or length of stay and a decrease in narcotic requirements on the day of surgery.

Patient Perceptions of Reimbursement for Arthroscopic Meniscectomy and Anterior Cruciate Ligament Reconstruction.

Historically, patient perceptions of surgeon reimbursement have been exaggerated compared with actual reimbursement. There is limited information about patient perceptions of physician reimbursement for arthroscopic meniscectomy and anterior cruciate ligament (ACL) reconstruction. This study evaluated patient perceptions of physician reimbursement for these procedures and compared perceptions of health care reform between urban and suburban clinics. Surveys were given to 231 consecutive patients, and patients were asked how much they believed a surgeon should be reimbursed for arthroscopic meniscectomy and ACL reconstruction as well as their perception of actual Medicare reimbursement to physicians. Patients were then informed of the actual reimbursement rates and asked additional questions about health care reform. Survey responses were compared in an urban setting vs a suburban setting. On average, patients reported that surgeons should receive $8096 for meniscectomy and $11,794 for ACL reconstruction. Patients estimated that Medicare paid physicians $5442 for meniscectomy and $6667 for ACL reconstruction. In addition, 65% of patients believed that reimbursement for meniscectomy was too low, and 57% of patients believed that reimbursement for ACL reconstruction was too low. Fewer than 2% of patients believed that surgeon salaries should be cut, and 75% believed that orthopedic surgeons should be paid more for subspecialty training. No differences were found in patients' perceptions of reimbursement or health care reform between urban and suburban settings. Patients perceived that the values of meniscectomy and ACL reconstruction were substantially higher than current Medicare reimbursement values and that surgeon salaries should not be cut. [Orthopedics. 2016; 39(5):e904-e910.].

Differentiation of rat adipose tissue-derived stem cells into neuron-like cells by valproic acid, a histone deacetylase inhibitor.

Valproic acid (VPA) is a widely used antiepileptic drug, which has recently been reported to modulate the neuronal differentiation of adipose tissue-derived stem cells (ASCs) in humans and dogs. However, controversy exists as to whether VPA really acts as an inducer of neuronal differentiation of ASCs. The present study aimed to elucidate the effect of VPA in neuronal differentiation of rat ASCs. One or three days of pretreatment with VPA (2 mM) followed by neuronal induction enhanced the ratio of immature neuron marker ßIII-tubulin-positive cells in a time-dependent manner, where the majority of cells also had a positive signal for neurofilament medium polypeptide (NEFM), a mature neuron marker. RT-PCR analysis revealed increases in the mRNA expression of microtubule-associated protein 2 (MAP2) and NEFM mature neuron markers, even without neuronal induction. Three-days pretreatment of VPA increased acetylation of histone H3 of ASCs as revealed by immunofluorescence staining. Chromatin immunoprecipitation assay also showed that the status of histone acetylation at H3K9 correlated with the gene expression of TUBB3 in ASCs by VPA. These results indicate that VPA significantly promotes the differentiation of rat ASCs into neuron-like cells through acetylation of histone H3, which suggests that VPA may serve as a useful tool for producing transplantable cells for future applications in clinical treatments.

Pitching performance and longevity after revision ulnar collateral ligament reconstruction in Major League Baseball pitchers.

BACKGROUND: Medial ulnar collateral ligament (UCL) reconstruction is a common procedure performed on professional pitchers in Major League Baseball (MLB). Although a great deal is known about primary reconstruction, much less is known about revision reconstruction. PURPOSE/HYPOTHESIS: The purpose of this study was to evaluate statistical performance, return to play, and career longevity in MLB pitchers after revision UCL surgery, with the hypothesis that pitching performance and career longevity will decline after revision surgery. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: A total of 33 MLB pitchers who underwent revision UCL reconstruction surgery (UCL-R group) were identified and compared with 33 age- and position-matched controls (CTL group). Return to play, total years played, and statistical performance were evaluated and compared with controls. RESULTS: After revision surgery, 65.5% of UCL-R pitchers returned to the MLB level. On average, the UCL-R pitchers played 0.8 years less in the majors (P<.01) than did the control pitchers. The UCL-R pitchers who returned to the MLB level had a similar earned run average (UCL-R: 4.88, CTL: 4.76, P=.82) and walks/hits per innings pitched (UCL-R: 1.58, CTL: 1.44, P=.22) compared with the control pitchers. There were significant declines, however, in terms of innings pitched (UCL-R: 36.95, CTL: 75.00, P<.01), walks per 9 innings (UCL-R: 4.75, CTL: 3.49, P<.01), and wins (UCL-R: 1.88, CTL: 4.10, P<.01) as well as nonsignificant declines in wins above replacement (UCL-R: 0.25, CTL: 0.62, P=.06) and runs above replacement (UCL-R: 3.26, CTL: 6.91, P=.07). CONCLUSION: MLB pitchers who undergo UCL-R have a low rate of return to MLB play and have shortened careers after return. Pitchers who returned to the MLB level maintained performance in several statistics such as earned run average and walks/hits per innings pitched; however, pitchers returned with a significantly decreased workload.

Booster effect of canine distemper, canine parvovirus infection and infectious canine hepatitis combination vaccine in domesticated adult dogs.

Domesticated adult dogs with antibody titer classified as below 'high' to one or more of canine distemper virus (CDV), canine parvovirus type-2 (CPV-2) and canine adenovirus type-1 (CAdV-1) were then given an additional inoculation, and the effectiveness of this booster evaluated 2 months later. Consequently, CDV and CAdV-1 antibody titer experienced a significant increase, but the same effect was not observed in the antibody titer of CPV-2. These findings suggest that with additional inoculation, a booster effect may be expected in increasing antibody titers for CDV and CAdV-1, but it is unlikely to give an increase in CPV-2 antibody titer.

Effects of body weight on antibody titers against canine parvovirus type 2, canine distemper virus, and canine adenovirus type 1 in vaccinated domestic adult dogs.

The objective of this study was to determine whether post-vaccination antibody titers vary according to body weight in adult dogs. Antibody titers against canine parvovirus type 2 (CPV-2), canine distemper virus (CDV), and canine adenovirus type 1 (CAdV-1) were measured for 978 domestic adult dogs from 2 to 6 y of age. The dogs had been vaccinated approximately 12 mo earlier with a commercial combination vaccine. The dogs were divided into groups according to their weight. It was found that mean antibody titers in all weight groups were sufficient to prevent infection. Intergroup comparison, however, revealed that CPV-2 antibody titers were significantly higher in the Super Light (< 5 kg) group than in the Medium (10 to 19.9 kg) and Heavy (> 20 kg) groups and were also significantly higher in the Light (5 to 9.9 kg) group than in the Heavy group. Antibody titers against CDV were significantly higher in the Super Light, Light, and Medium groups than in the Heavy group. There were no significant differences among the groups for the CAdV-1 antibody titers.

Pour vérifier que les taux d'anticorps chez des chiens vaccinés changeaient en fonction de leur poids après la vaccination par un vaccin commercial combiné, on a mesuré les anticorps antivirus de la parvovirose canine (CPV-2), de la maladie de Carré (CDV) et de l'encéphalite de Rubarth ­ type-1 (CAdV-1) chez 978 chiens de compagnie agés de 2 à 6 ans, un an après leur vaccination. Par nos mesures, nous observons dans tous les groupes un taux satisfaisant d' immunisation moyen des animaux. Mais en comparant les groupes de poids, on s'aperçoit que pour la parvovirose canine CPV-2, le groupe des super-légers (< 5 kg) est significativement plus protégé en anticorps que les groupes de poids moyen (de 10 à 19,9 kg) et de poids le plus lourd (> 20 kg). De même les poids légers (de 5 à 9,9 kg) sont significativement mieux protégés que les poids lourds. Pour la maladie de Carré (CDV), les super-légers, les poids légers ou les groupes de poids moyen ont un taux d'anticorps significativement plus élevé que les plus lourds. Par contre pour l'Encéphalite de Rubarth (CAdV-1) aucune différence des taux d'anticorps dans les groupes de poids n'a été observée.(Traduit par les auteurs).

Antibody titers for canine parvovirus type-2, canine distemper virus, and canine adenovirus type-1 in adult household dogs.

Serum antibody titers for canine parvovirus type-2 (CPV-2), canine distemper virus (CDV) and canine adenovirus type-1 (CAV-1) were investigated in 1031 healthy adult household dogs (2 to 18 years old) given an annual inoculation in the previous 11 to 13 months. The number of dogs retaining significant titers of antibodies against CPV-2, CDV, and CAV-1 were 888 (86%), 744 (72%), and 732 (71%), respectively. There were no differences between males and females in antibody titers against the 3 viruses. Antibody titer for CPV-2 was significantly higher in younger dogs than in older dogs, CDV antibody was significantly higher in older dogs than in younger dogs, and CAV titer was not associated with age.

Ethylene insensitivity impedes a subset of responses to phosphorus deficiency in tomato and petunia.

The role of ethylene in growth and developmental responses to low phosphorus stress was evaluated using ethylene-insensitive 'Never-ripe' (Nr) tomato and etr1 petunia plants. Low phosphorus increased adventitious root formation in 'Pearson' (wild-type) tomato plants, but not in Nr, supporting a role for ethylene in adventitious root development and showing that ethylene is important for this aspect of phosphorus response. Low phosphorus reduced ethylene production by adventitious roots of both genotypes, suggesting that ethylene perception--not production--regulates carbon allocation to adventitious roots at the expense of other roots under low phosphorus stress. With the exception of its effect on adventitious rooting, Nr had positive effects on growth and biomass accumulation in tomato whereas etr1 tended to have negative effects on petunia. This was particularly evident during the recovery from transplanting, when the effective quantum yield of photosystem II of etr1 petunia grown with low phosphorus was significantly lower than 'Mitchell Diploid', suggesting that etr1 petunia plants may undergo more severe post-transplant stress at low phosphorus availability. Our results demonstrate that ethylene mediates adventitious root formation in response to phosphorus stress and plays an important role for quick recovery of plants exposed to multiple environmental stresses, i.e. transplanting and low phosphorus.

Ethylene modulates genetic, positional, and nutritional regulation of root plagiogravitropism.

Plagiogravitropic growth of roots strongly affects root architecture and topsoil exploration, which are important for the acquisition of water and nutrients. Here we show that basal roots of Phaseolus vulgaris L. develop from 2-3 definable whorls at the root-shoot interface and exhibit position-dependent plagiogravitropic growth. The whorl closest to the shoot produces the shallowest roots, and lower whorls produce deeper roots. Genotypes vary in both the average growth angles of roots within whorls and the range of growth angles, i.e. the difference between the shallowest and deepest basal roots within a root system. Since ethylene has been implicated in both gravitropic and edaphic stress responses, we studied the role of ethylene and its interaction with phosphorus availability in regulating growth angles of genotypes with shallow or deep basal roots. There was a weak correlation between growth angle and ethylene production in the basal rooting zone, but ethylene sensitivity was strongly correlated with growth angle. Basal roots emerging from the uppermost whorl were more responsive to ethylene treatment than the lower-most whorl, displaying shallower angles and inhibition of growth. Ethylene sensitivity is greater for shallow than for deep genotypes and for plants grown with low phosphorus compared with those supplied with high phosphorus. Ethylene exposure increased the range of angles, although deep genotypes grown in low phosphorus were less affected. Our results identify basal root whorl number as a novel architectural trait, and show that ethylene mediates regulation of growth angle by position of origin, genotype and phosphorus availability.

Assessment of inequality of root hair density in Arabidopsis thaliana using the Gini coefficient: a close look at the effect of phosphorus and its interaction with ethylene.

BACKGROUND AND AIMS: Root hair density (i.e. the number of root hairs per unit root length) in Arabidopsis thaliana varies among individual plants in response to different nutrient stresses. The degree of such variation, defined as inequality, serves as a unique indicator of the uniformity of response within a plant population to nutrient availability. METHODS: Using the Gini coefficient (G) as an inequality index, the inequality of root hair density in Arabidopsis thaliana 'Columbia' was evaluated under conditions of nutrient stresses; in particular the effect of phosphorus and its interaction with ethylene. KEY RESULTS: With decreasing phosphorus concentration, root hair density increased while inequality decreased logarithmically. The addition of the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC) under high phosphorus increased root hair density and decreased inequality by 7-fold. Inhibition of ethylene action with 1-methylcyclopropene (MCP) and silver thiosulphate (STS) under low phosphorus decreased root hair density, and increased inequality by 9-fold and 4-fold, respectively. The ethylene action inhibitors had little effect on root hair density under high phosphorus, but inequality increased 3-fold in the presence of MCP and decreased 2-fold in the presence of STS. Compared with the control, deficiencies in S, N and K increased inequality of root hair density, whereas deficiencies in P, Ca, B, Mn, Fe, Zn, Cu and Mg decreased inequality. In particular, the inequality of root hair density increased by over 2-fold under deficiencies of N or K, but decreased 14-fold under phosphorus deficiency. CONCLUSIONS: The inequality analysis indicates a strong correlation between prevalent signals from the environment (i.e. phosphorus stress) and the response of the plant, and the role of ethylene in this response. As the environmental signals become stronger, an increasing proportion of individuals respond, resulting in a decrease in variation in responsiveness among individual plants as indicated by reduced inequality.

Ethylene and phosphorus availability have interacting yet distinct effects on root hair development.

The hypothesis that ethylene participates in the regulation of root hair development by phosphorus availability in Arabidopsis thaliana was tested by chemically manipulating ethylene synthesis and response and with ethylene-insensitive mutants. Low phosphorus-induced root hair development could be mimicked by adding the ethylene precursor, 1-aminocyclopropane-1-carboxylate (ACC), to high phosphorus media, and inhibited by adding ethylene inhibitors to low phosphorus media. Ethylene-insensitive mutants showed a reduced response to low phosphorus, indicating ethylene involvement in root hair responses to phosphorus deficiency. To dissect the nature of this involvement, the morphological and anatomical changes associated with increased root hair density were investigated. Growth in low phosphorus resulted in smaller, more numerous cortical cells, resulting in a larger number of root hair-bearing epidermal cell files. Cortical cell number was not affected by ethylene inhibitors, ACC, or mutations reducing ethylene sensitivity in roots grown with low phosphorus, indicating that ethylene does not participate in this response. The exception was the eir1 mutation, which strongly reduced this change in radial anatomy, supporting a role for polar auxin transport in this process. Trichoblast cell length was reduced by low phosphorus availability in all genotypes, but even more so for ein2-1 and ein4. The proportion of epidermal cells forming hairs and root hair length were reduced in ethylene-insensitive mutants, especially in the presence of low phosphorus. These results demonstrate multiple effects of low phosphorus from the earliest stages of root hair development, and cross-talk between ethylene and phosphorus in the control of a subset of the low phosphorus effects, concentrating on those later in development.