Gene Stacking and Stoichiometric Expression of ER-Targeted Constructs Using "2A" Self-Cleaving Peptides

Simultaneous stoichiometric expression of multiple genes plays a major part in modern research and biotechnology. Traditional methods for incorporating multiple transgenes (or "gene stacking") have drawbacks such as long time frames, uneven gene expression, gene silencing, and segregation derived from the use of multiple promoters. 2A self-cleaving peptides have emerged over the last two decades as a functional gene stacking method and have been used in plants for the co-expression of multiple genes under a single promoter. Here we describe design features of multicistronic polyproteins using 2A peptides for co-expression in plant cells and targeting to the endoplasmic reticulum (ER). We designed up to quad-cistronic vectors that could target proteins in tandem to the ER. We also exemplify the incorporation of self-excising intein domains within 2A polypeptides, to remove residue additions. These features could aid in the design of stoichiometric protein co-expression strategies in plants in combination with targeting to different subcellular compartments.

Quantitation of ER Morphology and Dynamics

The plant endoplasmic reticulum forms a network of tubules connected by three-way junctions or sheet-like cisternae. Although the network is three-dimensional, in many plant cells, it is constrained to thin volume sandwiched between the vacuole and plasma membrane, effectively restricting it to a 2-D planar network. The structure of the network, and the morphology of the tubules and cisternae can be automatically extracted following intensity-independent edge-enhancement and various segmentation techniques to give an initial pixel-based skeleton, which is then converted to a graph representation. ER dynamics can be determined using optical flow techniques from computer vision or persistency analysis. Collectively, this approach yields a wealth of quantitative metrics for ER structure and can be used to describe the effects of pharmacological treatments or genetic manipulation. The software is publicly available.

A five-gene qPCR signature can classify type 2 asthma comparably to microscopy of induced sputum from severe asthma patients

Asthma is a heterogenous disease characterized by airway inflammation and variable expiratory airflow limitation resulting in variable respiratory symptoms. Characterization of airway inflammation is important to choose the optimal treatment for severe asthma patients eligible for biological treatment. However, counting cells in induced sputum samples are a time-consuming process, highly dependent on personal skills. Replacing eosinophil and neutrophil cell counting with qPCR for transcripts of selected mast cell, and basophil genes may provide more reproducible results.

Aims

The objective of this study was to compare qPCR with microscopy in asthma endotyping.

Methods

A qPCR method measuring five mast cell/basophil genes was applied on induced sputum samples from 30 severe asthma patients and compared with microscopy. Target gene Ct-values (CPA3, GATA2, HDC, MS4A2, TPSAB1/TPSB2) were referenced to household β-actin Ct values as a measure of relative mRNA abundance of the target in each sample. Target/β-actin-ratios in eosinophilic and non-eosinophilic groups determined by microscopy with an eosinophil threshold of 3% in 400 cells were compared using Mann-Whitney U Test. Spearman´s correlations were used to test for correlation between targets vs. FENO and targets vs. blood eosinophil counts.

Results

The study demonstrated a statistical difference in relative mRNA abundance for four mast cell/basophil specific genes. CPA3, GATA2, HDC and MS4A2 were elevated in eosinophilic asthma versus non-eosinophilic asthma patients. The study found that GATA2, CPA3, MS4A2 and TPSAB1/TPSB2 transcripts are positively correlated with FENO. Neither the five mast cell genes nor the five-gene signature correlated with blood eosinophils. The five-gene signature with a target/β-actin-ratio cut-off ≥2 generated sensitivity = 87%, specificity = 94%, NPV = 88% and PPV = 92% compared to microscopy.

Conclusion

This study confirms the contribution of mast cells in the pathogenesis of EA and suggests that mast cell mRNA markers could be one of the biomarkers used to identify EA.

Dynamic calcium-mediated stress response and recovery signatures in the fungal pathogen, Candida albicans

IMPORTANCE

Intracellular calcium signaling plays an important role in the resistance and adaptation to stresses encountered by fungal pathogens within the host. This study reports the optimization of the GCaMP fluorescent calcium reporter for live-cell imaging of dynamic calcium responses in single cells of the pathogen, Candida albicans, for the first time. Exposure to membrane, osmotic or oxidative stress generated both specific changes in single cell intracellular calcium spiking and longer calcium transients across the population. Repeated treatments showed that calcium dynamics become unaffected by some stresses but not others, consistent with known cell adaptation mechanisms. By expressing GCaMP in mutant strains and tracking the viability of individual cells over time, the relative contributions of key signaling pathways to calcium flux, stress adaptation, and cell death were demonstrated. This reporter, therefore, permits the study of calcium dynamics, homeostasis, and signaling in C. albicans at a previously unattainable level of detail.

Recombinant expression and subcellular targeting of the particulate methane monooxygenase (pMMO) protein components in plants

Methane is a potent greenhouse gas, which has contributed to approximately a fifth of global warming since pre-industrial times. The agricultural sector produces significant methane emissions, especially from livestock, waste management and rice cultivation. Rice fields alone generate around 9% of total anthropogenic emissions. Methane is produced in waterlogged paddy fields by methanogenic archaea, and transported to the atmosphere through the aerenchyma tissue of rice plants. Thus, bioengineering rice with catalysts to detoxify methane en route could contribute to an efficient emission mitigation strategy. Particulate methane monooxygenase (pMMO) is the predominant methane catalyst found in nature, and is an enzyme complex expressed by methanotrophic bacteria. Recombinant expression of pMMO has been challenging, potentially due to its membrane localization, multimeric structure, and polycistronic operon. Here we show the first steps towards the engineering of plants for methane detoxification with the three pMMO subunits expressed in the model systems tobacco and Arabidopsis. Membrane topology and protein-protein interactions were consistent with correct folding and assembly of the pMMO subunits on the plant ER. Moreover, a synthetic self-cleaving polypeptide resulted in simultaneous expression of all three subunits, although low expression levels precluded more detailed structural investigation. The work presents plant cells as a novel heterologous system for pMMO allowing for protein expression and modification.

Spatial and temporal control of mitochondrial H2 O2 release in intact human cells

Hydrogen peroxide (H₂O₂) has key signaling roles at physiological levels, while causing molecular damage at elevated concentrations. H₂O₂ production by mitochondria is implicated in regulating processes inside and outside these organelles. However, it remains unclear whether and how mitochondria in intact cells release H₂O₂. Here, we employed a genetically encoded high‐affinity H₂O₂ sensor, HyPer7, in mammalian tissue culture cells to investigate different modes of mitochondrial H₂O₂ release. We found substantial heterogeneity of HyPer7 dynamics between individual cells. We further observed mitochondria‐released H₂O₂ directly at the surface of the organelle and in the bulk cytosol, but not in the nucleus or at the plasma membrane, pointing to steep gradients emanating from mitochondria. Gradient formation is controlled by cytosolic peroxiredoxins, which act redundantly and with a substantial reserve capacity. Dynamic adaptation of cytosolic thioredoxin reductase levels during metabolic changes results in improved H₂O₂ handling and explains previously observed differences between cell types. Our data suggest that H₂O₂‐mediated signaling is initiated only in close proximity to mitochondria and under specific metabolic conditions.

Comparative Effectiveness Analyses of Salvage Prostatectomy and Salvage Radiotherapy Outcomes Following Focal or Whole-Gland Ablative Therapy (High-Intensity Focused Ultrasound, Cryotherapy or Electroporation) for Localised Prostate Cancer

AIMS

Ablative therapy, such as focal therapy, cryotherapy or electroporation, aims to treat clinically significant prostate cancer with reduced treatment-related toxicity. Up to a third of patients may require further local salvage treatment after ablative therapy failure. Limited descriptive, but no comparative, evidence exists between different salvage treatment outcomes. The aim of this study was to compare oncological and functional outcomes after salvage robot-assisted radical prostatectomy (SRARP) and salvage radiotherapy (SRT).

MATERIALS AND METHODS

Data were collected prospectively and retrospectively on 100 consecutive SRARP cases and 100 consecutive SRT cases after ablative therapy failure in a high-volume tertiary centre.

RESULTS

High-risk patients were over-represented in the SRARP group (66.0%) compared with the SRT group (48.0%) (P = 0.013). The median (interquartile range) follow-up after SRARP was 16.5 (10.0-30.0) months and 37.0 (18.5-64.0) months after SRT. SRT appeared to confer greater biochemical recurrence-free survival at 1, 2 and 3 years compared with SRARP in high-risk patients (year 3: 86.3% versus 66.0%), but biochemical recurrence-free survival was similar for intermediate-risk patients (year 3: 90.0% versus 75.6%). There was no statistical difference in pad-free continence at 12 and 24 months between SRARP (77.2 and 84.7%) and SRT (75.0 and 74.0%) (P = 0.724, 0.114). Erectile function was more likely to be preserved in men who underwent SRT. After SRT, cumulative bowel and urinary Radiation Therapy Oncology Group toxicity grade I were 25.0 and 45.0%, grade II were 11.0 and 11.0% and grade III or IV complications were 4.0 and 5.0%, respectively.

CONCLUSION

We report the first comparative analyses of salvage prostatectomy and radiotherapy following ablative therapy. Men with high-risk disease appear to have superior oncological outcomes after SRT; however, treatment allocation does not appear to influence oncological outcomes for men with intermediate-risk disease. Treatment allocation was associated with a different spectrum of toxicity profile. Our data may inform shared decision-making when considering salvage treatment following focal or whole-gland ablative therapy.

734 Evaluation of A Webinar Based Surgical Teaching Course (EDUCATE) - A Prospective Cohort Study

Aim

Anecdotal evidence suggests Foundation Year (FY) doctors start surgical rotations with less confidence than medical rotations. The study aimed to determine the effect of a national webinar-based surgical teaching course on participants’ confidence, and to assess attitudes surrounding undergraduate surgical education.

Method

This prospective cohort study is reported with reference to STROBE guidelines and received ethical approval. A series of 15 free-access webinars was developed based on the Royal College of Surgeons Undergraduate Curriculum. An expert-validated questionnaire was used to collect data before and after the course. Inclusion criteria were UK-based medical students and FY doctors who attended at least one webinar. The primary outcome was confidence in completing common tasks during surgical rotations.

Results

Completed pre-course (484) and post-course (352) questionnaires yielded 92 paired samples (63% female). 85% were medical students, representing 29 UK universities, and 15% FY doctors. Mean confidence in assessing, investigating, and implementing initial management of surgical conditions was greater after the intervention (p ≤ 0.001). Mean confidence in managing on-call tasks and starting a surgical FY job was also higher post-course greater (p ≤ 0.001). These improvements correlated with webinar attendance (p ≤ 0.05). 27.1% of participants were satisfied with the quality of undergraduate surgical education. 22.9% agreed that surgical placements prepared them well to manage surgical tasks.

Conclusions

Medical students and FY doctors report low confidence and feel unprepared in managing surgical tasks. Additionally, they report poor satisfaction with undergraduate surgical education. This shortfall may be improved through delivery of a national, accessible, targeted online webinar series and curriculum.

141 New Guidelines to Reduce Unnecessary Blood Tests, Delayed Discharge and Costs Following Robot Assisted Radical Prostatectomy

Objectives

Routine postoperative blood tests (POBT) following robot assisted radical prostatectomy (RARP) are used to evaluate the impact of surgery on pre-existing co-morbidities and to detect early complications. This practice dates back to an era of open surgery, when blood loss and complication rates were higher. We propose new guidelines to improve the specificity of POBT.

Method

The cases of 1040 consecutive patients who underwent a primary or salvage RARP at two large tertiary urology centres in the United Kingdom were retrospectively reviewed to form new guidelines. The new guidelines were prospectively validated in a sample of 300 patients.

Results

Derivation Dataset: 3% and 5% had intra- and post-operative Clavien-Dindo complications, respectively. 15% had clinical concerns postoperatively. 0.9% required perioperative transfusion. 78% had routine blood tests without clinical concerns, none of whom developed a complication. 98% of complications were suspected by clinical judgement. 6% of patients had a discharge delay of ≥ 1 day due to delayed or incomplete blood tests. Validation Dataset: No significant difference existed in complication, clinical concern or transfusion rates between the derivation and validation datasets. Number of POBT requested reduced by 73% (p < 0.001). The new guidelines improved POBT sensitivity for complications from 98% to 100% and specificity from 0% to 74%. Discharge delays reduced from 6% to 0% (p = 0.008). Cost savings were £178 per patient.

Conclusions

Postoperative complications and transfusion following RARP are rare. Routine POBT without clinical indication are unnecessary and inefficient. A guideline-based approach to POBT can reduce costs and optimise discharge without compromising patient safety or care.

283 Salvage Versus Primary Robot-Assisted Radical Prostatectomy: A Propensity-Matched Comparative Effectiveness Study from A High-Volume Tertiary Centre

Aim

Salvage Robot-Assisted Radical Prostatectomy (sRARP) is a potential treatment option for locally recurrent Prostate Cancer after non-surgical primary treatment. There are minimal data comparing outcomes between propensity-matched salvage and primary Robot-Assisted Radical Prostatectomy (RARP). We compare perioperative, oncological, and functional outcomes of sRARP with primary RARP and between sRARP post-whole and focal gland therapy.

Method

1:1 propensity-matched comparison of 146 sRARP with primary RARP from a cohort of 3,852 consecutive patients from a high-volume tertiary centre.

Results

There were no significant differences in patient characteristics between the salvage and primary RARP groups. Grade III-V Clavien-Dindo complication rates were 1.3% and 0% in the salvage and primary groups, respectively (p = 0.310). Median (IQR) follow-up was 16 (10,30) and 21 (13,33) months in the salvage and primary groups, respectively. BCR rates were 30.8% and 13.7% in the salvage and primary groups, respectively (p < 0.001). Pad-free continence rates were 79.1% and 85.4% at two years in the salvage and primary groups, respectively (p = 0.160). ED rates were 95.2% and 77.4% in the salvage and primary groups, respectively (p < 0.001). Comparing the whole gland and focal gland groups, BCR rates were 33.3% and 29.1%, respectively (p = 0.687), pad-free continence rates were 66% and 89.3%, respectively (p = 0.001), and ED rates were 98.3% and 93%, respectively (p = 0.145).

Conclusions

SRARP has similar perioperative but inferior oncological outcomes to primary RARP. Continence rates are similar to primary RARP, but potency is worse. Perioperative and oncological outcomes of sRARP after focal gland therapy are similar but continence outcomes are superior compared to sRARP after whole gland therapy.

81 VIRTUAL: Virtual Interactive Surgical Skills Classroom – An Ongoing Randomized Controlled Trial

Introduction

High costs and inaccessibility are significant barriers to face-to-face basic surgical skills (BSS) training. Virtual classrooms enable the combination of computer-based learning with interactive expert instruction. They may optimise resources and increase accessibility, facilitating larger-scale training with a similar educational benefit. We aim to evaluate the efficacy of virtual BSS classroom training compared to both non-interactive video and face-to-face teaching.

Method

72 medical students will be randomly assigned to three equal intervention groups based on year group and surgical skill confidence. Interventions will be implemented following an instructional video. Group A will practice independently, Group B will receive face-to-face training, and Group C will attend a virtual classroom. Participants will be recorded placing three interrupted sutures with hand tied knots pre- and post-intervention, and Objective Structured Assessment of Technical Skills (OSATS) will be blind marked by two experts. Change in confidence, time to completion and a granular performance score will also be measured. Each intervention’s feasibility and accessibility will be assessed.

Results

Data collection will be completed in January 2021. Significant improvement in OSATS within groups will be indicative of intervention quality. Difference in improvement between groups will determine the relative performance of the interventions.

Conclusions

To our knowledge, this will be the largest randomised control trial investigating virtual BSS classroom training. It will serve as a comprehensive appraisal of the virtual classroom’s suitability as an alternative to face-to-face training. The findings will assist the development and implementation of further resource-efficient training programs during the COVID-19 pandemic and in the future.

1420 ViRtual prOficiency Based prOgression for Robotic Training (VROBOT): A Prospective Cohort Study Protocol

Introduction

Robotic surgery is an evolving field that requires specialist training. Historically, robotic surgery training has lacked standardisation. Recently, training centres have introduced proficiency-based modules and curriculums to certify and progress the skills of novice robotic surgeons. However, training tends to be self-directed and non-interactive. Limited interactive teaching does exist but can be inaccessible and expensive. We aim to validate the effectiveness of the current Fundamentals of Robotic Surgery (FRS) training curriculum with the addition of interactive virtual classroom teaching.

Method

16 novice surgical trainees will be assigned to two training groups. The interventions will be implemented following a one-week robotic skills induction. Both groups will receive access to the FRS curriculum for one week. The intervention group will additionally receive virtual classroom robotic skills training. The primary outcome will be the objective performance scores after training using a synthetic model based on task errors, time taken and contact pressure. In week 3, each group will receive the alternate intervention and objective performance scores will be measured to determine the trajectory of scores.

Results

Significant objective performance improvement following the intervention will be indicative of intervention quality.

Conclusions

This will be the first feasibility study evaluating the efficacy of interactive virtual robotic surgery training. It will determine the effect size of virtual classroom training on the development of basic robotic surgical skills in addition to the proficiency-based FRS curriculum. The findings will assist the development and implementation of further resource-efficient virtual robotic surgical skills training programs.

O43 Virtual: virtual interactive surgical skills classroom: a randomized controlled trial (protocol)

Introduction

High costs and inaccessibility are significant barriers to face-to-face basic surgical skills (BSS) training. Virtual classrooms enable the combination of computer-based learning with interactive expert instruction. They may optimise resources and increase accessibility, facilitating larger-scale training with a similar educational benefit. We aim to evaluate the efficacy of virtual BSS classroom training compared to both non-interactive video and face-to-face teaching.

Method

72 medical students will be randomly assigned to three equal intervention groups based on surgical skills experience and confidence. Interventions will be implemented following an instructional video. Group A will practice independently, Group B will receive face-to-face training, and Group C will attend a virtual classroom. Participants will be recorded placing three interrupted sutures with hand tied knots pre- and post-intervention. Objective Structured Assessment of Technical Skills (OSATS) will be blind marked by two experts.

Result

Change in confidence, time to completion and a novel granular performance score will also be measured. Each intervention’s feasibility and accessibility will be assessed. Significant improvement in OSATS within groups will be indicative of intervention quality. Difference in improvement between groups will determine the relative performance of the interventions.

Conclusion

This will be the largest randomised control trial investigating virtual BSS classroom training. It will serve as a comprehensive appraisal of the suitability of virtual classrooms as an alternative to face-to-face training. The findings will assist the development and implementation of further resource-efficient training programs during the COVID-19 pandemic and beyond.

Take-home Message

This is the first RCT assessing virtual basic surgical skill classroom training and serves as a comprehensive appraisal of the suitability of virtual classrooms as an alternative to face-to-face training. The findings will assist the development and implementation of further resource-efficient training programs during the COVID-19 pandemic and in the future.

O50 New guidelines to reduce unnecessary blood tests, delayed discharge and costs following robot assisted radical prostatectomy

Introduction

Routine postoperative blood tests (POBT) are used to evaluate the impact of surgery on pre-existing co-morbidities and to detect early complications. This practice dates back to an era of open surgery, when blood loss and complication rates were higher. We propose new guidelines to improve the specificity of POBT.

Method

The cases of 1040 consecutive patients who underwent a primary or salvage RARP at two large tertiary urology centres in the United Kingdom were retrospectively reviewed, and new guidelines were designed. The guidelines were prospectively validated in a cohort of 300 patients.

Result

Derivation Dataset 3% and 5% had intra- and post-operative Clavien-Dindo complications, respectively. 15% had clinical concerns postoperatively. 0.9% required perioperative transfusion. 78% had routine blood tests without clinical concerns, none of whom developed a complication. 98% of complications were suspected by clinical judgement. 6% of patients had a discharge delay of ≥ 1 days due to delayed or incomplete blood tests.

Validation Dataset No significant difference existed in complication, clinical concern or transfusion rates between the derivation and validation datasets. New guidelines improved sensitivity for complications from 98% to 100% and specificity from 0% to 74%. The number of blood tests requested reduced by 73% (P < 0.001). Discharge delays reduced from 6% to 0% (P = 0.008). Cost savings were £178 per patient.

Conclusion

Postoperative complications and transfusion following RARP are rare. Routine POBT without clinical indication are unnecessary and inefficient. A guideline-based approach to POBT can reduce costs and optimise discharge without compromising patient safety or care.

Take-home Message

Routine postoperative blood tests following robot assisted radical prostatectomy are often unnecessary. A guideline-based approach can reduce costs and optimise patient care.

429 National Evaluation of Confidence and Preparedness for Surgical Rotations in Medical Students and Foundation Year Doctors

Introduction

Limited published and anecdotal evidence suggests foundation year (FY) doctors start their surgical rotations with lower confidence than medical rotations. This may be due to insufficient undergraduate practical teaching related to common surgical rotations. This study aimed to evaluate the confidence and preparedness for surgical rotations of medical students and FY doctors.

Method

An expert-validated questionnaire was distributed nationally to UK medical students and FY doctors. The primary outcome was confidence in completing common tasks during surgical rotations.

Results

491 participants (84% medical students, 16% FYs) were recruited from 36 UK medical schools. 80% were likely to pursue a career in surgery however only 7% felt confident about starting a surgical FY job. 66% felt neutral or unsatisfied about the quality of medical school surgical teaching, and 80% indicated that placements did not prepare them well to manage common FY surgical tasks. The internal reliability of the questionnaire was high (=0.939).

Conclusions

Medical students and FY doctors lack confidence and preparation for surgical jobs. High-quality, practically grounded educational courses such as the National Surgical Teaching Society (NSTS) webinar curriculum could improve confidence and preparedness for surgical rotations. Further research evaluating the benefits of such courses is warranted.

Automated and accurate segmentation of leaf venation networks via deep learning

Leaf vein network geometry can predict levels of resource transport, defence and mechanical support that operate at different spatial scales. However, it is challenging to quantify network architecture across scales due to the difficulties both in segmenting networks from images and in extracting multiscale statistics from subsequent network graph representations. Here we developed deep learning algorithms using convolutional neural networks (CNNs) to automatically segment leaf vein networks. Thirty-eight CNNs were trained on subsets of manually defined ground-truth regions from >700 leaves representing 50 southeast Asian plant families. Ensembles of six independently trained CNNs were used to segment networks from larger leaf regions (c. 100 mm² ). Segmented networks were analysed using hierarchical loop decomposition to extract a range of statistics describing scale transitions in vein and areole geometry. The CNN approach gave a precision-recall harmonic mean of 94.5% ± 6%, outperforming other current network extraction methods, and accurately described the widths, angles and connectivity of veins. Multiscale statistics then enabled the identification of previously undescribed variation in network architecture across species. We provide a LeafVeinCNN software package to enable multiscale quantification of leaf vein networks, facilitating the comparison across species and the exploration of the functional significance of different leaf vein architectures.

Linking functional traits to multiscale statistics of leaf venation networks

Leaf venation networks evolved along several functional axes, including resource transport, damage resistance, mechanical strength, and construction cost. Because functions may depend on architectural features at different scales, network architecture may vary across spatial scales to satisfy functional tradeoffs. We develop a framework for quantifying network architecture with multiscale statistics describing elongation ratios, circularity ratios, vein density, and minimum spanning tree ratios. We quantify vein networks for leaves of 260 southeast Asian tree species in samples of up to 2 cm² , pairing multiscale statistics with traits representing axes of resource transport, damage resistance, mechanical strength, and cost. We show that these multiscale statistics clearly differentiate species' architecture and delineate a phenotype space that shifts at larger scales; functional linkages vary with scale and are weak, with vein density, minimum spanning tree ratio, and circularity ratio linked to mechanical strength (measured by force to punch) and elongation ratio and circularity ratio linked to damage resistance (measured by tannins); and phylogenetic conservatism of network architecture is low but scale-dependent. This work provides tools to quantify the function and evolution of venation networks. Future studies including primary and secondary veins may uncover additional insights.

Quantitative analysis of plant ER architecture and dynamics

The endoplasmic reticulum (ER) is a highly dynamic polygonal membrane network composed of interconnected tubules and sheets (cisternae) that forms the first compartment in the secretory pathway involved in protein translocation, folding, glycosylation, quality control, lipid synthesis, calcium signalling, and metabolon formation. Despite its central role in this plethora of biosynthetic, metabolic and physiological processes, there is little quantitative information on ER structure, morphology or dynamics. Here we describe a software package (AnalyzER) to automatically extract ER tubules and cisternae from multi-dimensional fluorescence images of plant ER. The structure, topology, protein-localisation patterns, and dynamics are automatically quantified using spatial, intensity and graph-theoretic metrics. We validate the method against manually-traced ground-truth networks, and calibrate the sub-resolution width estimates against ER profiles identified in serial block-face SEM images. We apply the approach to quantify the effects on ER morphology of drug treatments, abiotic stress and over-expression of ER tubule-shaping and cisternal-modifying proteins.

MSL1 is a mechanosensitive ion channel that dissipates mitochondrial membrane potential and maintains redox homeostasis in mitochondria during abiotic stress

Mitochondria must maintain tight control over the electrochemical gradient across their inner membrane to allow ATP synthesis while maintaining a redox-balanced electron transport chain and avoiding excessive reactive oxygen species production. However, there is a scarcity of knowledge about the ion transporters in the inner mitochondrial membrane that contribute to control of membrane potential. We show that loss of MSL1, a member of a family of mechanosensitive ion channels related to the bacterial channel MscS, leads to increased membrane potential of Arabidopsis mitochondria under specific bioenergetic states. We demonstrate that MSL1 localises to the inner mitochondrial membrane. When expressed in Escherichia coli, MSL1 forms a stretch-activated ion channel with a slight preference for anions and provides protection against hypo-osmotic shock. In contrast, loss of MSL1 in Arabidopsis did not prevent swelling of isolated mitochondria in hypo-osmotic conditions. Instead, our data suggest that ion transport by MSL1 leads to dissipation of mitochondrial membrane potential when it becomes too high. The importance of MSL1 function was demonstrated by the observation of a higher oxidation state of the mitochondrial glutathione pool in msl1-1 mutants under moderate heat- and heavy-metal-stress. Furthermore, we show that MSL1 function is not directly implicated in mitochondrial membrane potential pulsing, but is complementary and appears to be important under similar conditions.

The Specification of Geometric Edges by a Plant Rab GTPase Is an Essential Cell-Patterning Principle During Organogenesis in Arabidopsis

Plant organogenesis requires control over division planes and anisotropic cell wall growth, which each require spatial patterning of cells. Polyhedral plant cells can display complex patterning in which individual faces are established as biochemically distinct domains by endomembrane trafficking. We now show that, during organogenesis, the Arabidopsis endomembrane system specifies an important additional cellular spatial domain: the geometric edges. Previously unidentified membrane vesicles lying immediately beneath the plasma membrane at cell edges were revealed through localization of RAB-A5c, a plant GTPase of the Rab family of membrane-trafficking regulators. Specific inhibition of RAB-A5c activity grossly perturbed cell geometry in developing lateral organs by interfering independently with growth anisotropy and cytokinesis without disrupting default membrane trafficking. The initial loss of normal cell geometry can be explained by a failure to maintain wall stiffness specifically at geometric edges. RAB-A5c thus meets a requirement to specify this cellular spatial domain during organogenesis.

Nitric oxide generated by the rice blast fungus Magnaporthe oryzae drives plant infection

Plant-derived nitric oxide (NO) triggers defence, priming the onset of the hypersensitive response and restricting pathogen ingress during incompatibility. However, little is known about the role of pathogen-produced NO during pre-infection development and infection. We sought evidence for NO production by the rice blast fungus during early infection. NO production was measured using fluorescence of DAR-4M and the role of NO assessed using NO scavengers. The synthesis of NO was investigated by targeted knockout of genes potentially involved in NO synthesis, including nitric oxide synthase-like genes (NOL2 and NOL3) and nitrate (NIA1) and nitrite reductase (NII1), generating single and double Δnia1Δnii1, Δnia1Δnol3, and Δnol2Δnol3 mutants. We demonstrate that Magnaporthe oryzae generates NO during germination and in early development. Removal of NO delays germling development and reduces disease lesion numbers. NO is not generated by the candidate proteins tested, nor by other arginine-dependent NO systems, by polyamine oxidase activity or non-enzymatically by low pH. Furthermore, we show that, while NIA1 and NII1 are essential for nitrate assimilation, NIA1, NII1, NOL2 and NOL3 are all dispensable for pathogenicity. Development of M. oryzae and initiation of infection are critically dependent on fungal NO synthesis, but its mode of generation remains obscure.

Physiological significance of network organization in fungi

The evolution of multicellularity has occurred in diverse lineages and in multiple ways among eukaryotic species. For plants and fungi, multicellular forms are derived from ancestors that failed to separate following cell division, thus retaining cytoplasmic continuity between the daughter cells. In networked organisms, such as filamentous fungi, cytoplasmic continuity facilitates the long-distance transport of resources without the elaboration of a separate vascular system. Nutrient translocation in fungi is essential for nutrient cycling in ecosystems, mycorrhizal symbioses, virulence, and substrate utilization. It has been proposed that an interconnected mycelial network influences resource translocation, but the theory has not been empirically tested. Here we show, by using mutants that disrupt network formation in Neurospora crassa (Δso mutant, no fusion; ΔPrm-1 mutant, ∼50% fusion), that the translocation of labeled nutrients is adversely affected in homogeneous environments and is even more severely impacted in heterogeneous environments. We also show that the ability to share resources and genetic exchange between colonies (via hyphal fusion) is very limited in mature colonies, in contrast to in young colonies and germlings that readily share nutrients and genetic resources. The differences in genetic/resource sharing between young and mature colonies were associated with variations in colony architecture (hyphal differentiation/diameters, branching patterns, and angles). Thus, the ability to share resources and genetic material between colonies is developmentally regulated and is a function of the age of a colony. This study highlights the necessity of hyphal fusion for efficient nutrient translocation within an N. crassa colony but also shows that established N. crassa colonies do not share resources in a significant manner.

Contrast-independent curvilinear structure detection in biomedical images

Many biomedical applications require detection of curvilinear structures in images and would benefit from automatic or semiautomatic segmentation to allow high-throughput measurements. Here, we propose a contrast-independent approach to identify curvilinear structures based on oriented phase congruency, i.e., the phase congruency tensor (PCT). We show that the proposed method is largely insensitive to intensity variations along the curve and provides successful detection within noisy regions. The performance of the PCT is evaluated by comparing it with state-of-the-art intensity-based approaches on both synthetic and real biological images.

An increase in serum tryptase even below 11.4 ng/mL may indicate a mast cell-mediated hypersensitivity reaction: a prospective study in Hymenoptera venom allergic patients

BACKGROUND

During a systemic hypersensitivity reaction (SR), an increase in serum tryptase compared to the baseline value is an indicator of mast cell activation, most often due to an IgE-mediated mechanism.

OBJECTIVE

To study the relevance of an increase in serum tryptase below the upper normal value of 11.4 ng/mL.

METHODS

Serum tryptase levels were measured in 35 patients with Hymenoptera venom hypersensitivity before and during venom exposure. Of these, 20 developed SR to stings or following venom injections during immunotherapy (reactors), while 15 tolerated reexposure to stings or venom injections during immunotherapy without SR (non-reactors). Serum tryptase was estimated at 2, 5 and 24 h after exposure and was compared to a baseline value obtained before or at least 72 h after exposure.

RESULTS

Considering circadian variation of serum tryptase, a relative increase to ≥135% of the baseline value (relative delta bound) was defined to indicate mast cell activation. Such an increase was observed in 17 of 20 reactors (85%), but none of 15 non-reactors. A serum tryptase of ≥11.4 ng/mL following venom exposure was observed in eight of the 20 reactors (40%) and 2 (13.3%) of the 15 non-reactors. Both these non-reactors also had an elevated baseline serum tryptase.

CONCLUSIONS AND CLINICAL RELEVANCE

Serum tryptase values obtained during a suspected hypersensitivity reaction must always be compared to a baseline value. A relative tryptase increase to ≥135% of the baseline value during a suspected hypersensitivity reaction indicates mast cell activation even below 11.4 ng/mL.

Prevalence of emetic Bacillus cereus in different ice creams in Bavaria

In this study, 809 samples of ice cream from different sources were investigated by using cultural methods for the presence of presumptive Bacillus cereus. Isolates from culture-positive samples were examined with a real-time PCR assay targeting a region of the cereulide synthetase gene (ces) that is highly specific for emetic B. cereus strains. The samples were collected from ice cream parlors and restaurants that produced their own ice cream and from international commercial ice cream companies in different regions of Bavaria during the summer of 2008. Presumptive B. cereus was found in 508 (62.7%) ice cream samples investigated, and 24 (4.7%) of the isolates had the genetic background for cereulide toxin production. The level of emetic B. cereus in the positive samples ranged from 0.1 to 20 CFU/g of ice cream.

Imaging of long-distance alpha-aminoisobutyric acid translocation dynamics during resource capture by Serpula lacrymans

alpha-Aminoisobutyric acid (AIB) is a nonmetabolized amino acid analogue of alanine, which at low (muM) concentrations acts as a tracer for amino acid movements. At high concentrations (mM), it competitively inhibits membrane transport and metabolism of protein amino acids and acts as a systemic translocated inhibitor of mycelial extension in fungi. AIB can control mycelial spread of the basidiomycete Serpula lacrymans, the cause of brown rot of wood in buildings. However, it is not known how effectively the inhibitor is distributed throughout the mycelium. Realistically heterogeneous microcosms, in which the fungus grew across nutritionally inert sand to colonize discrete wood resources, were used to investigate patterns of inhibition and translocation following local application of AIB. At a 0.1 M concentration, locally applied AIB caused immediate arrest of extension throughout the whole mycelium, maintained for a 6-week experimental period. The dynamics of translocation of subtoxic amounts of [1-(14)C]AIB ([(14)C]AIB) were mapped by photon-counting scintillation imaging in conjunction with destructive harvest to establish the velocity, direction, and rate of translocation and the extent of [(14)C]AIB reallocation accompanying the invasion of fresh wood. Locally applied [(14)C]AIB was distributed throughout complex mycelial networks within 2 h of application, becoming localized in growing margins by 12 h. Encounter with a fresh wood resource triggered a widespread response, causing withdrawal of [(14)C]AIB from throughout the network, accompanied by accumulation in the newly colonized wood and associated mycelium. The results are discussed in the context of nutrient dynamics in wood decomposer fungi and the mechanism of the amino acid reallocation response.

A novel therapeutic option in Cogan diseases? TNF-alpha blockers

Cogan's syndrome is characterized by noninfectious, interstitial keratitis combined with a vestibulo-auditory deficit. Despite therapy with corticosteroids in combination with immunosuppressive agents, relapses occurred in two subjects and the clinical course suggested a progression of the disease. Treatment with anti-TNF-alpha was started leading to a rapid and sustained clinical remission for over 2 respectively 3 years.

Ratiometric fluorescence-imaging assays of plant membrane traffic using polyproteins

Fluorescent protein markers are widely used to report plant membrane traffic; however, effective protocols to quantify fluorescence or marker expression are lacking. Here the 20 residue self-cleaving 2A peptide from Foot and Mouth Disease Virus was used to construct polyproteins that expressed a trafficked marker in fixed stoichiometry with a reference protein in a different cellular compartment. Various pairs of compartments were simultaneously targeted. Together with a bespoke image analysis tool, these constructs allowed biosynthetic membrane traffic to be assayed with markedly improved sensitivity, dynamic range and statistical significance using protocols compatible with the common plant transfection and transgenic systems. As marker and effector expression could be monitored in populations or individual cells, saturation phenomena could be avoided and stochastic or epigenetic influences could be controlled. Surprisingly, mutational analysis of the ratiometric assay constructs revealed that the 2A peptide was dispensable for efficient cleavage of polyproteins carrying a single internal signal peptide, whereas the signal peptide was essential. In contrast, a construct bearing two signal peptide/anchors required 2A for efficient separation and stability, but 2A caused the amino-terminal moiety of such fusions to be mis-sorted to the vacuole. A model to account for the behaviour of 2A in these and other studies in plants is proposed.

Interplay between function and structure in complex networks

We show that abrupt structural transitions can arise in functionally optimal networks, driven by small changes in the level of transport congestion. Our results offer an explanation as to why so many diverse species of network structure arise in nature (e.g., fungal systems) under essentially the same environmental conditions. Our findings are based on an exactly solvable model system which mimics a variety of biological and social networks. We then extend our analysis by introducing a renormalization scheme involving cost motifs, to describe analytically the average shortest path across multiple-ring-and-hub networks. As a consequence, we uncover a "skin effect" whereby the structure of the inner multi-ring core can cease to play any role in terms of determining the average shortest path across the network.

Quantitative fluorescence microscopy: from art to science

A substantial number of elegant experimental approaches have been developed to image the distribution and dynamics of DNA, mRNA, proteins, organelles, metabolites, and ions in living plant cells. Although the human brain can rapidly assimilate visual information, particularly when presented as animations and movies, it is much more challenging to condense the phenomenal amount of data present in three-, four-, or even five-dimensional images into statistically useful measurements. This review explores a range of in vivo fluorescence imaging applications in plants, with particular emphasis on where quantitative techniques are beginning to emerge.

[Emergency due to allergy: the therapy--adrenaline for physicians and patients]

Emergency due to allergy may proceed within minutes to life-threatening respiratory and circulatory problems. Therefore, after diagnosis prompt and correct therapy might be vital. Because of its effect on alpha-, beta1-, and beta2-receptors, adrenaline is the treatment of choice in emergency due to allergy. For fear of cardiovascular side effects, often adrenaline is withheld even in case of anaphylaxis. If given properly such as an intramuscular injection the danger of undesirable side effects, however, is small. After a systemic, allergic reaction each patient needs to be equipped with rescue medications. If an adrenaline-containing device is prescribed--nowadays with EpiPen and the metered-dose inhaler Primatene Mist 2 systems are available--, the patient must get a correct instruction in its use. In case of a severe allergic reaction, antihistamines and corticosteroids are given in second line. Following any systemic allergy, an allergological work-up should be required. Only through exact diagnosis and profound patient's education, recurrences can be avoided, and in some cases, specific immunotherapy is indicated.

Quantitative in vivo measurement of glutathione in Arabidopsis cells

A new, non-destructive assay is described to quantify cytoplasmic glutathione (GSH) levels in vivo in single cells or populations of cells from Arabidopsis suspension cultures. Cytoplasmic GSH was labelled with monochlorobimane (MCB) in situ to give a fluorescent GSH-bimane (GSB) conjugate. At low (10-100 microM) concentrations of MCB, labelling was mediated by a glutathione S-transferase, which confers specificity for GSH. HPLC analysis of MCB-labelled low molecular-weight thiols showed that the assay measures the total GSH pool, including the oxidized glutathione. The progress curve for the labelling could be described using Michaelis-Menten kinetics with an apparent KM of 40 microM and Vmax of 470 micromol lcyt -1 min-1. There was no evidence for de novo synthesis of GSH during the labelling period of 2 h, suggesting that control of GSH synthesis is not mediated by feedback control of gamma-glutamylcysteine synthetase in this system. The total cellular level of GSH was calculated from the plateau value of the progress curve, after appropriate calibration, as 830-942 nmol g-1 FW. The volume fraction of cytoplasm was measured from serial optical sections of bimane-labelled cells collected by confocal laser scanning microscopy (CLSM) with excitation 442 nm, or two-photon laser scanning microscopy (TPLSM) with excitation 770 nm. A value of 42 +/- 3% cytoplasm was determined by manual segmentation, and a value of 37 +/- 2% using stereological techniques. Using these figures, values for cytoplasmic [GSH] were estimated to be between 2.7 +/- 0.3 and 3.2 +/- 0.3 mM for cell populations. In addition, measurement of GSH levels in individual cells using CLSM and TPLSM gave values of 3.0 +/- 0.5 and 3.5 +/- 0.7 mM, respectively.

Glutathione biosynthesis in Arabidopsis trichome cells

In Arabidopsis thaliana, trichome cells are specialized unicellular structures with uncertain functions. Based on earlier observations that one of the genes involved in cysteine biosynthesis (Atcys-3A) is highly expressed in trichomes, we have extended our studies in trichome cells to determine their capacity for glutathione (GSH) biosynthesis. First, we have analyzed by in situ hybridization the tissue-specific expression of the genes Atcys-3A and sat5, which encode O-acetylserine(thio)lyase (OASTL) and serine acetyltransferase (SAT), respectively, as well as gsh1 and gsh2, which encode gamma-glutamylcysteine synthetase and glutathione synthetase, respectively. The four genes are highly expressed in leaf trichomes of Arabidopsis, and their mRNA accumulate to high levels. Second, we have directly measured cytoplasmic GSH concentration in intact cells by laser-scanning microscopy after labeling with monochlorobimane as a GSH-specific probe. From these measurements, cytosolic GSH concentrations of 238+/-25, 80+/-2, and 144+/-19 microM were estimated for trichome, basement, and epidermal cells, respectively. Taking into account the volume of the cells measured using stereological techniques, the trichomes have a total GSH content more than 300-fold higher than the basement and epidermal cells. Third, after NaCl treatment, GSH biosynthesis is markedly decreased in trichomes. Atcys-3A, sat5, gsh1, and gsh2 mRNA levels show a decrease in transcript abundance, and [GSH](cyt) is reduced to 47+/-5 microM. These results suggest the important physiological significance of trichome cells related to GSH biosynthesis and their possible role as a sink during detoxification processes.

The role of calcium in blue-light-dependent chloroplast movement in lemna trisulca L

Chloroplast movements are a normal physiological response to changes in light intensity and provide a good model system to analyse the signal transduction pathways following light perception. Blue-light-dependent chloroplast movements were observed in Lemna trisulca using confocal optical sectioning and 3-D reconstruction or photometric measurements of leaf transmission. Chloroplasts moved away from strong blue light (SBL) towards the anticlinal walls (profile position), and towards the periclinal walls (face position) under weak blue light (WBL) over about 20-40 min. Cytoplasmic calcium ([Ca2 + ]cyt) forms part of the signalling system in response to SBL as movements were associated with small increases in [Ca2 + ]cyt and were blocked by antagonists of calcium homeostasis, including EGTA, nifedipine, verapamil, caffeine, thapsigargin, TFP (trifluoperazine), W7 and compound 48/80. Treatments predicted to affect internal Ca2 + stores gave the most rapid and pronounced effects. In addition, artificially increasing [Ca2 + ]cyt in darkness using the Ca2 + ionophore A23187 and high external Ca2 + (or Sr2 + ), triggered partial movement of chloroplasts to profile position analogous to a SBL response. These data are all consistent with [Ca2 + ]cyt acting as a signal in SBL responses; however, the situation is more complex given that both WBL and SBL responses were inhibited to a similar extent by all the Ca2 + -signalling antagonists used. As the direction of chloroplast movement in WBL is exactly opposite to that in SBL, we conclude that, whilst proper regulation of [Ca2 + ]cyt homeostasis is critical for both SBL and WBL responses, additional factors may be required to specify the direction of chloroplast movement.

Light perception and the role of the xanthophyll cycle in blue-light-dependent chloroplast movements in lemna trisulca L

In most higher plants, chloroplasts move towards the periclinal cell walls in weak blue light (WBL) to increase light harvesting for photosynthesis, and towards the anticlinal walls as an escape reaction, thus avoiding photo-damage in strong blue light (SBL). The photo- receptor(s) triggering these responses have not yet been identified. In this study, the role of zeaxanthin as a blue-light photoreceptor in chloroplast movements was investigated. Time-lapse 3D confocal imaging in Lemna trisulca showed that individual chloroplasts responded to local illumination when one half of the cell was treated with light of different intensity or spectral quality to that received by the other half, or was maintained in darkness. Thus the complete signal perception, transduction and effector system has a high degree of spatial resolution and is consistent with localization of part of the transduction chain in the chloroplasts. Turnover of xanthophylls was determined using HPLC, and a parallel increase was observed between zeaxanthin and chloroplast movements in SBL. Ascorbate stimulated both a transient increase in zeaxanthin levels and chloroplast movement to profile in physiological darkness. Conversely, dithiothreitol blocked zeaxanthin production and responses to SBL and, to a lesser extent, WBL. Norflurazon preferentially inhibited SBL-dependent chloroplast movements. Increases in zeaxanthin were also observed in strong red light (SRL) when no directional chloroplast movements occurred. Thus it appears that a combination of zeaxanthin and blue light is required to trigger responses. Blue light can cause cis-trans isomerization of xanthophylls, thus photo-isomerization may be a critical link in the signal transduction pathway.

Successful immunotherapy with T-cell epitope peptides of bee venom phospholipase A2 induces specific T-cell anergy in patients allergic to bee venom

BACKGROUND

Specific immunotherapy with honeybee venom (BV) is highly effective, but allergic side effects can occur during treatment. Immunotherapy with peptides containing major T-cell epitopes of the relevant allergen or allergens provides an alternative strategy without these problems.

OBJECTIVE

The study investigates the immunologic mechanisms and clinical effects of immunotherapy with T-cell epitope peptides of the major BV allergen, the phospholipase A2 (PLA).

METHODS

Five patients with IgE-mediated systemic allergic reactions to bee stings were treated with a mixture of three T-cell epitope peptides of PLA. Ten patients allergic to BV receiving whole BV immunotherapy served as control subjects. Increasing doses of the peptide mixture, up to a maintenance dose of 100 microg, were administered subcutaneously within 2 months. The patients were then challenged with PLA and 1 week later with a bee sting. The cellular and humoral immune response was measured in vitro.

RESULTS

No allergic side effects were caused by the peptide immunotherapy, and all patients tolerated the challenge with PLA without systemic allergic symptoms. Two patients developed mild systemic allergic reactions after the bee sting challenge. After peptide immunotherapy, specific proliferative responses to PLA and the peptides in peripheral blood mononuclear cells were decreased in successfully treated patients. The production of TH2 and TH1 cytokines was inhibited, and B cells were not affected in their capacity to produce specific IgE and IgG4 antibodies. Their levels increased after allergen challenge in favor of IgG4.

CONCLUSIONS

Immunotherapy of BV allergy with short T-cell peptides of PLA induces epitope-specific anergy in peripheral T cells and changes the specific isotype ratio in a fashion similar to that of conventional immunotherapy in successfully treated patients.

Increased specificity of diagnostic tests with recombinant major bee venom allergen phospholipase A2

BACKGROUND

In diagnosis of type I allergy recombinant allergens have potential advantages over conventional allergenic extracts, both regarding specificity and reproducibility.

OBJECTIVES

We therefore decided to study honey bee venom (BV) and its major allergen phospholipase A2 (PLA) in native and recombinant form for diagnosis of bee sting allergy.

METHOD

We investigated 85 patients with a history of a recent systemic allergic bee sting reaction and positive intracutaneous skin test to BV, and 21 controls with no history of allergic bee sting reaction and negative skin test to BV. Intracutaneous skin tests and determination of specific IgE by ImmunoCAP(R) to BV, native PLA (nPLA) and recombinant PLA (rPLA) were done in all patients and controls.

RESULTS

In skin testing 84 (99%) of the 85 patients reacted to nPLA and 81 (95%) to rPLA, while none of the 21 controls was positive with nPLA or rPLA. Specific serum IgE to BV could be detected in 82 of the patients (96%), to nPLA in 73 (86%) and to rPLA in 66 (78%). Four (19%) of the controls had a positive CAP to BV, one (4.8%) to nPLA and none to rPLA. Analysis of discordant results in CAP showed, that most patients with specific IgE to BV, but not to nPLA and rPLA, had positive skin tests to both PLA preparations and low levels of BV specific IgE. Patients with specific IgE to nPLA but not to rPLA were usually sensitized to minor allergens of BV which contaminated the commercial nPLA.

CONCLUSIONS

PLA is the major allergen in BV. While diagnostic tests with BV are more sensitive, the specificity of tests with PLA, especially rPLA is clearly increased as compared with BV.

Hymenoptera sting anaphylaxis and urticaria pigmentosa: clinical findings and results of venom immunotherapy in ten patients

BACKGROUND

Occasional patients with urticaria pigmentosa and anaphylaxis after Hymenoptera stings have been described. In this situation the question arises: Is anaphylaxis IgE-mediated or induced by pharmacologic mediator release from mast cells?

METHODS

We investigated 10 patients with histologically confirmed urticaria pigmentosa and a history of anaphylaxis after honeybee or Vespula stings before and during immunotherapy with the respective venom.

RESULTS

In eight of 10 patients, an elevated serum tryptase level was found. In two of 10 patients, no venom-specific IgE could be detected by either skin tests or RAST. Five patients had no detectable venom-specific serum IgE, and in the remaining patients the level was low (<1 Phadebas RAST unit). Venom immunotherapy was well tolerated and caused only one mild systemic reaction in a patient during the dose increase phase. Six patients were re-stung while receiving venom immunotherapy: only one had a mild systemic reaction (angioedema) after a Vespula sting.

CONCLUSION

Anaphylactic symptoms after Hymenoptera stings in patients with urticaria pigmentosa are most often IgE-mediated but can occasionally be observed in the absence of IgE sensitization to venom allergens. Venom immunotherapy can be safely and successfully used in patients with urticaria pigmentosa and sting anaphylaxis.

Cell proliferation and hair tip growth in the Arabidopsis root are under mechanistically different forms of redox control

We provide evidence that the tripeptide thiol glutathione (GSH) participates in the regulation of cell division in the apical meristem of Arabidopsis roots. Exogenous application of micromolar concentrations of GSH raised the number of meristematic cells undergoing mitosis, while depletion of GSH had the opposite effect. A role for endogenous GSH in the control of cell proliferation is also provided by mapping of GSH levels in the root meristem using the GSH-specific dye monochlorobimane and confocal laser scanning microscopy. High levels of GSH were associated with the epidermal and cortical initials and markedly lower levels in the quiescent center. The mechanisms controlling cell division could also be triggered by other reducing agents: ascorbic acid and dithiothreitol. Our data also reveal significant plasticity in the relationship between the trichoblast cell length and the hair it subtends in response to alterations in intracellular redox homeostasis. While mechanisms that control trichoblast elongation are influenced by nonspecific redox couples, root hair tip growth has a more specific requirement for sulfhydryl groups. The responses we describe here may represent the extremes of redox control of root plasticity and would allow the root to maintain exploration of the soil under adverse conditions with minimal cell divisions and root hair production or capitalize on a favorable environment by production of numerous long hairs. Redox sensing of the environment and subsequent redox-dependent modulation of growth and development may be crucial components in the strategies plants have evolved for survival in a fluctuating environment.