Investigating the microstructure of plant leaves in 3D with lab-based X-ray Computed Tomography

Background Leaf cellular architecture plays an important role in setting limits for carbon assimilation and, thus, photosynthetic performance. However, the low density, fine structure, and sensitivity to desiccation of plant tissue has presented challenges to its quantification. Classical methods of tissue fixation and embedding prior to 2D microscopy of sections is both laborious and susceptible to artefacts that can skew the values obtained. Here we report an image analysis pipeline that provides quantitative descriptors of plant leaf intercellular airspace using lab-based X-ray Computed Tomography (microCT). We demonstrate successful visualisation and quantification of differences in leaf intercellular airspace in 3D for a range of species (including both dicots and monocots) and provide a comparison with a standard 2D analysis of leaf sections. Results We used the microCT image pipeline to obtain estimates of leaf porosity and mesophyll exposed surface area (Smes) for three dicot species (Arabidopsis, tomato and pea) and three monocot grasses (barley, oat and rice). The imaging pipeline consisted of (1) a masking operation to remove the background airspace surrounding the leaf, (2) segmentation by an automated threshold in ImageJ and then (3) quantification of the extracted pores using the ImageJ ‘Analyze Particles’ tool. Arabidopsis had the highest porosity and lowest Smes for the dicot species whereas barley had the highest porosity and the highest Smes for the grass species. Comparison of porosity and Smes estimates from 3D microCT analysis and 2D analysis of sections indicates that both methods provide a comparable estimate of porosity but the 2D method may underestimate Smes by almost 50%. A deeper study of porosity revealed similarities and differences in the asymmetric distribution of airspace between the species analysed. Conclusions Our results demonstrate the utility of high resolution imaging of leaf intercellular airspace networks by lab-based microCT and provide quantitative data on descriptors of leaf cellular architecture. They indicate there is a range of porosity and Smes values in different species and that there is not a simple relationship between these parameters, suggesting the importance of cell size, shape and packing in the determination of cellular parameters proposed to influence leaf photosynthetic performance

Effectiveness of the Structured and Conventional Methods of Viva Examination in Medical Education: A Systematic Review and Meta-analysis

Introduction: Oral examination (viva voce) is one of the common assessment methods for medical students. Literature shows that Conventional Oral Examination (COE), is a widely adopted method and uses a consolidated scoring system. There came an alternative method, Structured Oral Examination (SOE) that uses the recommended rating scale (prevalidated questions and markings). The emergence of a new method raised the research question of whether the conventional or structured oral examination is effective in assessing medical students. Aim: To evaluate the effectiveness of traditional and structured viva voce examination across the specialties in medical education. Materials and Methods: A systematic review was conducted on 18 peer-reviewed articles about conventional and structured oral examination among medical students. Medical Education Research Study Quality Instrument (MERSQI) was used to assess the quality of evidence. Results: The level of evidence was moderate where the MERSQI score ranges from 7.5-15.5 for the 18 articles included in the review process. SOE overcomes COE by assessing students’ cognitive skills, communication skills, behaviour and attitude whereas COE principally assesses the recall knowledge. Analytical and reasoning power remains the predominant domain in SOE. With psychometric properties like good reliability, sensitivity and acceptability, SOE remains the best strategy for the evaluation of medical students. Pooled results in the forest plot showed no difference in the viva voce marks between COE and SOE with a mean difference of 0.46 (p=0.53). Conclusion: The review analysis revealed that there is no difference in the mean marks scored by COE and SOE. However, a SOE will allow examiners to assess the medical students’ learning achievement with no partiality, stress, and anxiety compared to COE

Comparative metatranscriptomics reveals kingdom level changes in the rhizosphere microbiome of plants

Plant–microbe interactions in the rhizosphere have important roles in biogeochemical cycling, and maintenance of plant health and productivity, yet remain poorly understood. Using RNA-based metatranscriptomics, the global active microbiomes were analysed in soil and rhizospheres of wheat, oat, pea and an oat mutant (sad1) deficient in production of anti-fungal avenacins. Rhizosphere microbiomes differed from bulk soil and between plant species. Pea (a legume) had a much stronger effect on the rhizosphere than wheat and oat (cereals), resulting in a dramatically different rhizosphere community. The relative abundance of eukaryotes in the oat and pea rhizospheres was more than fivefold higher than in the wheat rhizosphere or bulk soil. Nematodes and bacterivorous protozoa were enriched in all rhizospheres, whereas the pea rhizosphere was highly enriched for fungi. Metabolic capabilities for rhizosphere colonisation were selected, including cellulose degradation (cereals), H2 oxidation (pea) and methylotrophy (all plants). Avenacins had little effect on the prokaryotic community of oat, but the eukaryotic community was strongly altered in the sad1 mutant, suggesting that avenacins have a broader role than protecting from fungal pathogens. Profiling microbial communities with metatranscriptomics allows comparison of relative abundance, from multiple samples, across all domains of life, without polymerase chain reaction bias. This revealed profound differences in the rhizosphere microbiome, particularly at the kingdom level between plants