Preparation of plants for developmental and cellular imaging by light-sheet microscopy

Advances in posterity of visualization in paradigm of nano‐level ultra‐structures for nano–bio interaction studies

The progression in contemporary scientific field is facilitated by a multitude of sophisticated and cutting‐edge methodologies that are employed for various research purposes. Among these methodologies, microscopy stands out as a fundamental and essential technique utilized in scientific investigations. Moreover, due to the continuous evolution and enhancement of microscopic methodologies, nanotechnology has reached a highly developed stage within modern scientific realm, particularly renowned for its wide‐ranging applications in the fields of biomedicine and environmental science. When it comes to conducting comprehensive and in‐depth experimental analyses to explore the nanotechnological aspects relevant to biological applications, the concept of nano–biological interaction emerges as the focal point of any research initiative. Nonetheless, this particular study necessitates a meticulous approach toward imaging and visualization at diverse magnification levels to ensure accurate observations and interpretations. It is widely acknowledged that modern microscopy has emerged as a sophisticated and invaluable instrument in this regard. This review aims to provide a comprehensive discussion on the progress made in microscopic techniques specifically tailored for visualizing the interactions between nanostructures and biological entities, thereby facilitating the exploration of the practical applications of nanotechnology in the realm of biological sciences.

EasyClick: an improved system for confocal microscopy of live roots with a user-optimized sample holder

MAIN CONCLUSION

We describe a user-optimized sample holder EasyClick for medium-sized plants that reduces root side movements and thus greatly extends the duration of live cell confocal microscopy. Preparation and mounting of the samples are key factors for successful live cell microscopy. To acquire biologically relevant data, it is necessary to minimize stress and avoid physical damage to plant tissues during the installation of the sample into the microscope. This is challenging, particularly when the whole plant is mounted as the living sample needs to be properly anchored in the microscopic system to obtain high-quality and high-resolution data. Here, we present a user-optimized sample holder EasyClick for live cell inverted confocal microscopic analysis of plant roots with diameters from 0.3 to 0.7 mm. The EasyClick holder was tested on an inverted confocal microscope using germinating plants of several cereals. Nevertheless, it can be directly used on other types of inverted microscopes from various producers and on different plant species. The EasyClick holder effectively restricts root lateral and vertical movements. This greatly improves the conditions for time-lapse microscopy of the samples of interest.

Cytoskeleton as a roadmap navigating rhizobia to establish symbiotic root nodulation in legumes

Legumes enter into symbiotic associations with soil nitrogen-fixing rhizobia, culminating in the creation of new organs, root nodules. This complex process relies on chemical and physical interaction between legumes and rhizobia, including early signalling events informing the host legume plant of a potentially beneficial microbe and triggering the nodulation program. The great significance of this plant-microbe interaction rests upon conversion of atmospheric dinitrogen not accessible to plants into a biologically active form of ammonia available to plants. The plant cytoskeleton consists in a highly dynamic network and undergoes rapid remodelling upon sensing various developmental and environmental cues, including response to attachment, internalization, and accommodation of rhizobia in plant root and nodule cells. This dynamic nature is governed by cytoskeleton-associated proteins that modulate cytoskeletal behaviour depending on signal perception and transduction. Precisely localized cytoskeletal rearrangements are therefore essential for the uptake of rhizobia, their targeted delivery, and establishing beneficial root nodule symbiosis. This review summarizes current knowledge about rhizobia-dependent rearrangements and functions of the cytoskeleton in legume roots and nodules. General patterns and nodule type-, nodule stage-, and species-specific aspects of actin filaments and microtubules remodelling are discussed. Moreover, emerging evidence is provided about fine-tuning the root nodulation process through cytoskeleton-associated proteins. We also consider future perspectives on dynamic localization studies of the cytoskeleton during early symbiosis utilizing state of the art molecular and advanced microscopy approaches. Based on acquired detailed knowledge of the mutualistic interactions with microbes, these approaches could contribute to broader biotechnological crop improvement.

TurboID-based proteomic profiling of meiotic chromosome axes in Arabidopsis thaliana

During meiotic prophase I, sister chromatids are arranged in a loop-base array along a proteinaceous structure, called the meiotic chromosome axis. This structure is essential for synapsis and meiotic recombination progression and hence formation of genetically diverse gametes. Proteomic studies in plants aiming to unravel the composition and regulation of meiotic axes are constrained by limited meiotic cells embedded in floral organs. Here we report TurboID (TbID)-based proximity labelling (PL) in meiotic cells of Arabidopsis thaliana. TbID fusion to the two meiotic chromosome axis proteins ASY1 and ASY3 enabled the identification of their proximate 'interactomes' based on affinity purification coupled with mass spectrometry. We identified 39 ASY1 and/or ASY3 proximate candidates covering most known chromosome axis-related proteins. Functional studies of selected candidates demonstrate that not only known meiotic candidates but also new meiotic proteins were uncovered. Hence, TbID-based PL in meiotic cells enables the identification of chromosome axis proximate proteins in A. thaliana.

Advanced microscopy resolves dynamic localization patterns of stress-induced mitogen-activated protein kinase SIMK during alfalfa root hair interactions with Ensifer meliloti

Leguminous plants have established a mutualistic endosymbiotic interaction with nitrogen-fixing rhizobia to secure nitrogen sources in new specialised organs called root nodules. Before nodule formation, the development of early symbiotic structures is essential for rhizobia docking, internalization, targeted delivery and intracellular accommodation. We have recently reported that overexpression of stress-induced mitogen-activated protein kinase (SIMK) in alfalfa affects root hair, nodule and shoot formation, which raised the questions how SIMK may modulate these processes. In particular, detailed subcellular spatial distribution, activation and developmental relocation of SIMK during the early stages of alfalfa nodulation remain unclear. Here, we qualitatively and quantitatively characterised SIMK distribution patterns in Ensifer meliloti-infected root hairs using live-cell imaging and immunolocalization, employing alfalfa stable transgenic lines with genetically manipulated SIMK abundance and kinase activity. In the SIMKK-RNAi line, showing downregulation of SIMKK and SIMK, we found considerably decreased accumulation of phosphorylated SIMK around infection pockets and infection threads. However, this was strongly increased in the GFP-SIMK line, constitutively overexpressing GFP-tagged SIMK. Thus, genetically manipulated SIMK modulates root hair capacity to form infection pockets and infection threads. Employment of advanced light-sheet fluorescence microscopy (LSFM) on intact plants allowed gentle and non-invasive imaging of spatiotemporal interactions between root hairs and symbiotic Ensifer meliloti, while immunofluorescence detection confirmed that SIMK was activated in these locations. Our results shed new light on SIMK spatiotemporal participation in early interactions between alfalfa and Ensifer meliloti, and its internalization into root hairs, showing that local accumulation of active SIMK indeed modulates early nodulation in alfalfa.

Spatial proteomics of vesicular trafficking: coupling mass spectrometry and imaging approaches in membrane biology

In plants, membrane compartmentalization requires vesicle trafficking for communication among distinct organelles. Membrane proteins involved in vesicle trafficking are highly dynamic and can respond rapidly to changes in the environment and to cellular signals. Capturing their localization and dynamics is thus essential for understanding the mechanisms underlying vesicular trafficking pathways. Quantitative mass spectrometry and imaging approaches allow a system-wide dissection of the vesicular proteome, the characterization of ligand-receptor pairs and the determination of secretory, endocytic, recycling and vacuolar trafficking pathways. In this review, we highlight major proteomics and imaging methods employed to determine the location, distribution and abundance of proteins within given trafficking routes. We focus in particular on methodologies for the elucidation of vesicle protein dynamics and interactions and their connections to downstream signalling outputs. Finally, we assess their biological applications in exploring different cellular and subcellular processes.

Application of Chemical Inhibitors in Live Cell Imaging of Plant Meiosis Using Light Sheet Fluorescence Microscopy

Live imaging combined with the application of chemical inhibitors is a powerful research tool that enables researchers to precisely time the inhibition of cellular processes and study the consequences of these perturbations. This approach is usually applied to in vitro cultivated cells that are easily accessible to chemical treatments and microscopic observations. Here we describe a method for live cell imaging of Arabidopsis meiocytes embedded within floral organs combined with the application of a chemical drug at desired timepoints during meiosis. We describe a customized solution for the Zeiss Z.1 light sheet microscope, including sample preparation and data processing, and demonstrate its utility for the analysis of meiotic progression upon spindle inhibition.

Leaf microscopy applications in photosynthesis research: identifying the gaps

Leaf imaging via microscopy has provided critical insights into research on photosynthesis at multiple junctures, from the early understanding of the role of stomata, through elucidating C4 photosynthesis via Kranz anatomy and chloroplast arrangement in single cells, to detailed explorations of diffusion pathways and light utilization gradients within leaves. In recent decades, the original two-dimensional (2D) explorations have begun to be visualized in three-dimensional (3D) space, revising our understanding of structure-function relationships between internal leaf anatomy and photosynthesis. In particular, advancing new technologies and analyses are providing fresh insight into the relationship between leaf cellular components and improving the ability to model net carbon fixation, water use efficiency, and metabolite turnover rate in leaves. While ground-breaking developments in imaging tools and techniques have expanded our knowledge of leaf 3D structure via high-resolution 3D and time-series images, there is a growing need for more in vivo imaging as well as metabolite imaging. However, these advances necessitate further improvement in microscopy sciences to overcome the unique challenges a green leaf poses. In this review, we discuss the available tools, techniques, challenges, and gaps for efficient in vivo leaf 3D imaging, as well as innovations to overcome these difficulties.

ROOT HAIR DEFECTIVE 2 vesicular delivery to the apical plasma membrane domain during Arabidopsis root hair development

Arabidopsis (Arabidopsis thaliana) root hairs develop as long tubular extensions from the rootward pole of trichoblasts and exert polarized tip growth. The establishment and maintenance of root hair polarity is a complex process involving the local apical production of reactive oxygen species generated by A. thaliana nicotinamide adenine dinucleotide phosphate (NADPH) oxidase respiratory burst oxidase homolog protein C/ROOT HAIR-DEFECTIVE 2 (AtRBOHC/RHD2). Loss-of-function root hair defective 2 (rhd2) mutants have short root hairs that are unable to elongate by tip growth, and this phenotype is fully complemented by GREEN FLUORESCENT PROTEIN (GFP)-RHD2 expressed under the RHD2 promoter. However, the spatiotemporal mechanism of AtRBOHC/RHD2 subcellular redistribution and delivery to the plasma membrane (PM) during root hair initiation and tip growth are still unclear. Here, we used advanced microscopy for detailed qualitative and quantitative analysis of vesicular compartments containing GFP-RHD2 and characterization of their movements in developing bulges and growing root hairs. These compartments, identified by an independent molecular marker mCherry-VTI12 as the trans-Golgi network (TGN), deliver GFP-RHD2 to the apical PM domain, the extent of which corresponds with the stage of root hair formation. Movements of TGN/early endosomes, but not late endosomes, were affected in the bulging domains of the rhd2-1 mutant. Finally, we revealed that structural sterols might be involved in the accumulation, docking, and incorporation of TGN compartments containing GFP-RHD2 to the apical PM of root hairs. These results help in clarifying the mechanism of polarized AtRBOHC/RHD2 targeting, maintenance, and recycling at the apical PM domain, coordinated with different developmental stages of root hair initiation and growth.

ACORBA: Automated workflow to measure Arabidopsis thaliana root tip angle dynamics

The ability of plants to sense and orient their root growth towards gravity is studied in many laboratories. It is known that manual analysis of image data is subjected to human bias. Several semi-automated tools are available for analysing images from flatbed scanners, but there is no solution to automatically measure root bending angle over time for vertical-stage microscopy images. To address these problems, we developed ACORBA, which is an automated software that can measure root bending angle over time from vertical-stage microscope and flatbed scanner images. ACORBA also has a semi-automated mode for camera or stereomicroscope images. It represents a flexible approach based on both traditional image processing and deep machine learning segmentation to measure root angle progression over time. As the software is automated, it limits human interactions and is reproducible. ACORBA will support the plant biologist community by reducing labour and increasing reproducibility of image analysis of root gravitropism.

A label-free, fast and high-specificity technique for plant cell wall imaging and composition analysis

BACKGROUND

New cell wall imaging tools permit direct visualization of the molecular architecture of cell walls and provide detailed chemical information on wall polymers, which will aid efforts to use these polymers in multiple applications; however, detailed imaging and quantification of the native composition and architecture in the cell wall remains challenging.

RESULTS

Here, we describe a label-free imaging technology, coherent Raman scattering (CRS) microscopy, including coherent anti-Stokes Raman scattering (CARS) microscopy and stimulated Raman scattering (SRS) microscopy, which can be used to visualize the major structures and chemical composition of plant cell walls. We outline the major steps of the procedure, including sample preparation, setting the mapping parameters, analysis of spectral data, and image generation. Applying this rapid approach will help researchers understand the highly heterogeneous structures and organization of plant cell walls.

CONCLUSIONS

This method can potentially be incorporated into label-free microanalyses of plant cell wall chemical composition based on the in situ vibrations of molecules.

Plant multiscale networks: charting plant connectivity by multi-level analysis and imaging techniques

In multicellular and even single-celled organisms, individual components are interconnected at multiscale levels to produce enormously complex biological networks that help these systems maintain homeostasis for development and environmental adaptation. Systems biology studies initially adopted network analysis to explore how relationships between individual components give rise to complex biological processes. Network analysis has been applied to dissect the complex connectivity of mammalian brains across different scales in time and space in The Human Brain Project. In plant science, network analysis has similarly been applied to study the connectivity of plant components at the molecular, subcellular, cellular, organic, and organism levels. Analysis of these multiscale networks contributes to our understanding of how genotype determines phenotype. In this review, we summarized the theoretical framework of plant multiscale networks and introduced studies investigating plant networks by various experimental and computational modalities. We next discussed the currently available analytic methodologies and multi-level imaging techniques used to map multiscale networks in plants. Finally, we highlighted some of the technical challenges and key questions remaining to be addressed in this emerging field.

Extended field of view of light-sheet fluorescence microscopy by scanning multiple focus-shifted Gaussian beam arrays

Light-sheet fluorescence microscopy (LSFM) facilitates high temporal-spatial resolution, low photobleaching and phototoxicity for long-term volumetric imaging. However, when a high axial resolution or optical sectioning capability is required, the field of view (FOV) is limited. Here, we propose to generate a large FOV of light-sheet by scanning multiple focus-shifted Gaussian beam arrays (MGBA) while keeping the high axial resolution. The positions of the beam waists of the multiple Gaussian beam arrays are shifted in both axial and lateral directions in an optimized arranged pattern, and then scanned along the direction perpendicular to the propagation axis to form an extended FOV of light-sheet. Complementary beam subtraction method is also adopted to further improve axial resolution. Compared with the single Gaussian light-sheet method, the proposed method extends the FOV from 12 μm to 200 μm while sustaining the axial resolution of 0.73 μm. Both numerical simulation and experiment on samples are performed to verify the effectiveness of the method.

In vivo light-sheet microscopy resolves localisation patterns of FSD1, a superoxide dismutase with function in root development and osmoprotection

Superoxide dismutases (SODs) are enzymes detoxifying superoxide to hydrogen peroxide while temporal developmental expression and subcellular localisation are linked to their functions. Therefore, we aimed here to reveal in vivo developmental expression, subcellular, tissue- and organ-specific localisation of iron superoxide dismutase 1 (FSD1) in Arabidopsis using light-sheet and Airyscan confocal microscopy. FSD1-GFP temporarily accumulated at the site of endosperm rupture during seed germination. In emerged roots, it showed the highest abundance in cells of the lateral root cap, columella, and endodermis/cortex initials. The largest subcellular pool of FSD1-GFP was localised in the plastid stroma, while it was also located in the nuclei and cytosol. The majority of the nuclear FSD1-GFP is immobile as revealed by fluorescence recovery after photobleaching. We found that fsd1 knockout mutants exhibit reduced lateral root number and this phenotype was reverted by genetic complementation. Mutant analysis also revealed a requirement for FSD1 in seed germination during salt stress. Salt stress tolerance was coupled with the accumulation of FSD1-GFP in Hechtian strands and superoxide removal. It is likely that the plastidic pool is required for acquiring oxidative stress tolerance in Arabidopsis. This study suggests new developmental and osmoprotective functions of SODs in plants.

Tissue culture, genetic transformation, interaction with beneficial microbes, and modern bio-imaging techniques in alfalfa research

Current research needs to be more focused on agronomical plants to effectively utilize the knowledge obtained from model plant species. Efforts to improve legumes have long employed common breeding tools. Recently, biotechnological approaches facilitated the development of improved legumes with new traits, allowing them to withstand climatic changes and biotic stress. Owing to its multiple uses and profits, alfalfa (Medicago sativa L.) has become a prominent forage crop worldwide. This review provides a comprehensive research summary of tissue culture-based genetic transformation methods, which could be exploited for the development of transgenic alfalfa with agronomically desirable traits. Moreover, advanced bio-imaging approaches, including cutting-edge microscopy and phenotyping, are outlined here. Finally, characterization and the employment of beneficial microbes should help to produce biotechnologically improved and sustainable alfalfa cultivars.

MAGIC: Live imaging of cellular division in plant seedlings using lightsheet microscopy

Imaging technologies have been used to understand plant genetic and developmental processes, from the dynamics of gene expression to tissue and organ morphogenesis. Although the field has advanced incredibly in recent years, gaps remain in identifying fine and dynamic spatiotemporal intervals of target processes, such as changes to gene expression in response to abiotic stresses. Lightsheet microscopy is a valuable tool for such studies due to its ability to perform long-term imaging at fine intervals of time and at low photo-toxicity of live vertically oriented seedlings. In this chapter, we describe a detailed method for preparing and imaging Arabidopsis thaliana seedlings for lightsheet microscopy via a Multi-Sample Imaging Growth Chamber (MAGIC), which allows simultaneous imaging of at least four samples. This method opens new avenues for acquiring imaging data at a high temporal resolution, which can be eventually probed to identify key regulatory time points and any spatial dependencies of target developmental processes.

High-throughput 3D imaging of single cells with light-sheet fluorescence microscopy on chip

Single-cell analysis techniques are fundamental to study the heterogeneity of cellular populations, which is the basis to understand several biomedical mechanisms. Light-sheet fluorescence microscopy is a powerful technique for obtaining high-resolution imaging of individual cells, but the complexity of the setup and the sample mounting procedures limit its overall throughput. In our work, we present an optofluidic microscope-on-chip with integrated microlenses for light-sheet shaping and with a fluidic microchannel that allows the automatic and continuous delivery of samples of a few tens of microns in size. The device is used to perform dual-color fluorescence analysis and 3D reconstruction of xenograft-derived mouse breast cancer cells.

Imaging flowers: a guide to current microscopy and tomography techniques to study flower development

Developmental biology relies heavily on our ability to generate three-dimensional images of live biological specimens through time, and to map gene expression and hormone response in these specimens as they undergo development. The last two decades have seen an explosion of new bioimaging technologies that have pushed the limits of spatial and temporal resolution and provided biologists with invaluable new tools. However, plant tissues are difficult to image, and no single technology fits all purposes; choosing between many bioimaging techniques is not trivial. Here, we review modern light microscopy and computed projection tomography methods, their capabilities and limitations, and we discuss their current and potential applications to the study of flower development and fertilization.

Novel Imaging Modalities Shedding Light on Plant Biology: Start Small and Grow Big

The acquisition of quantitative information on plant development across a range of temporal and spatial scales is essential to understand the mechanisms of plant growth. Recent years have shown the emergence of imaging methodologies that enable the capture and analysis of plant growth, from the dynamics of molecules within cells to the measurement of morphometricand physiological traits in field-grown plants. In some instances, these imaging methods can be parallelized across multiple samples to increase throughput. When high throughput is combined with high temporal and spatial resolution, the resulting image-derived data sets could be combined with molecular large-scale data sets to enable unprecedented systems-level computational modeling. Such image-driven functional genomics studies may be expected to appear at an accelerating rate in the near future given the early success of the foundational efforts reviewed here. We present new imaging modalities and review how they have enabled a better understanding of plant growth from the microscopic to the macroscopic scale.

Super-resolution imaging of microtubules in Medicago sativa

Study of microtubules on cellular and subcellular levels is compromised by limited resolution of conventional fluorescence microscopy. However, it is possible to improve Abbe's diffraction-limited resolution by employment of super-resolution microscopy methods. Two of them, described herein, are structured-illumination microscopy (SIM) and Airyscan laser scanning microscopy (AM). Both methods allow high-resolution imaging of cortical microtubules in plant cells, thus contributing to the current knowledge on plant morphogenesis, growth and development. Both SIM and AM provide certain advantages and characteristic features, which are described here. We present immunofluorescence localization methods for microtubules in fixed plant cells achieving high signal efficiency, superb sample stability and sub-diffraction resolution. These protocols were developed for whole-mount immunolabeling of root samples of legume crop species Medicago sativa. They also contain tips for optimal sample preparation of plants germinated from seeds as well as plantlets regenerated from somatic embryos in vitro. We describe in detail all steps of optimized protocols for sample preparation, microtubule immunolabeling and super-resolution imaging.

Auxin-induced actin cytoskeleton rearrangements require AUX1

The actin cytoskeleton is required for cell expansion and implicated in cellular responses to the phytohormone auxin. However, the mechanisms that coordinate auxin signaling, cytoskeletal remodeling and cell expansion are poorly understood. Previous studies examined long-term actin cytoskeleton responses to auxin, but plants respond to auxin within minutes. Before this work, an extracellular auxin receptor - rather than the auxin transporter AUXIN RESISTANT 1 (AUX1) - was considered to precede auxin-induced cytoskeleton reorganization. In order to correlate actin array organization and dynamics with degree of cell expansion, quantitative imaging tools established baseline actin organization and illuminated individual filament behaviors in root epidermal cells under control conditions and after indole-3-acetic acid (IAA) application. We evaluated aux1 mutant actin organization responses to IAA and the membrane-permeable auxin 1-naphthylacetic acid (NAA). Cell length predicted actin organization and dynamics in control roots; short-term IAA treatments stimulated denser and more parallel, longitudinal arrays by inducing filament unbundling within minutes. Although AUX1 is necessary for full actin rearrangements in response to auxin, cytoplasmic auxin (i.e. NAA) stimulated a lesser response. Actin filaments became more 'organized' after IAA stopped elongation, refuting the hypothesis that 'more organized' actin arrays universally correlate with rapid growth. Short-term actin cytoskeleton response to auxin requires AUX1 and/or cytoplasmic auxin.

Imaging plant germline differentiation within Arabidopsis flowers by light sheet microscopy

In higher plants, germline differentiation occurs during a relatively short period within developing flowers. Understanding of the mechanisms that govern germline differentiation lags behind other plant developmental processes. This is largely because the germline is restricted to relatively few cells buried deep within floral tissues, which makes them difficult to study. To overcome this limitation, we have developed a methodology for live imaging of the germ cell lineage within floral organs of Arabidopsis using light sheet fluorescence microscopy. We have established reporter lines, cultivation conditions, and imaging protocols for high-resolution microscopy of developing flowers continuously for up to several days. We used multiview imagining to reconstruct a three-dimensional model of a flower at subcellular resolution. We demonstrate the power of this approach by capturing male and female meiosis, asymmetric pollen division, movement of meiotic chromosomes, and unusual restitution mitosis in tapetum cells. This method will enable new avenues of research into plant sexual reproduction.

Imaging plant germline differentiation within Arabidopsis flowers by light sheet microscopy

In higher plants, germline differentiation occurs during a relatively short period within developing flowers. Understanding of the mechanisms that govern germline differentiation lags behind other plant developmental processes. This is largely because the germline is restricted to relatively few cells buried deep within floral tissues, which makes them difficult to study. To overcome this limitation, we have developed a methodology for live imaging of the germ cell lineage within floral organs of Arabidopsis using light sheet fluorescence microscopy. We have established reporter lines, cultivation conditions, and imaging protocols for high-resolution microscopy of developing flowers continuously for up to several days. We used multiview imagining to reconstruct a three-dimensional model of a flower at subcellular resolution. We demonstrate the power of this approach by capturing male and female meiosis, asymmetric pollen division, movement of meiotic chromosomes, and unusual restitution mitosis in tapetum cells. This method will enable new avenues of research into plant sexual reproduction.

Spatiotemporal Pattern of Ectopic Cell Divisions Contribute to Mis-Shaped Phenotype of Primary and Lateral Roots of katanin1 Mutant

Pattern formation, cell proliferation, and directional cell growth, are driving factors of plant organ shape, size, and overall vegetative development. The establishment of vegetative morphogenesis strongly depends on spatiotemporal control and synchronization of formative and proliferative cell division patterns. In this context, the progression of cell division and the regulation of cell division plane orientation are defined by molecular mechanisms converging to the proper positioning and temporal reorganization of microtubule arrays such as the preprophase microtubule band, the mitotic spindle and the cytokinetic phragmoplast. By focusing on the tractable example of primary root development and lateral root emergence in Arabidopsis thaliana, genetic studies have highlighted the importance of mechanisms underlying microtubule reorganization in the establishment of the root system. In this regard, severe alterations of root growth, and development found in extensively studied katanin1 mutants of A. thaliana (fra2, lue1, and ktn1-2), were previously attributed to defective rearrangements of cortical microtubules and aberrant cell division plane reorientation. How KATANIN1-mediated microtubule severing contributes to tissue patterning and organ morphogenesis, ultimately leading to anisotropy in microtubule organization is a trending topic under vigorous investigation. Here we addressed this issue during root development, using advanced light-sheet fluorescence microscopy (LSFM) and long-term imaging of ktn1-2 mutant expressing the GFP-TUA6 microtubule marker. This method allowed spatial and temporal monitoring of cell division patterns in growing roots. Analysis of acquired multidimensional data sets revealed the occurrence of ectopic cell divisions in various tissues including the calyptrogen and the protoxylem of the main root, as well as in lateral root primordia. Notably the ktn1-2 mutant exhibited excessive longitudinal cell divisions (parallel to the root axis) at ectopic positions. This suggested that changes in the cell division pattern and the occurrence of ectopic cell divisions contributed significantly to pleiotropic root phenotypes of ktn1-2 mutant. LSFM provided evidence that KATANIN1 is required for the spatiotemporal control of cell divisions and establishment of tissue patterns in living A. thaliana roots.

Advanced Microscopy Reveals Complex Developmental and Subcellular Localization Patterns of ANNEXIN 1 in Arabidopsis

Annexin 1 (ANN1) is the most abundant member of the evolutionary conserved multigene protein superfamily of annexins in plants. Generally, annexins participate in diverse cellular processes, such as cell growth, differentiation, vesicle trafficking, and stress responses. The expression of annexins is developmentally regulated, and it is sensitive to the external environment. ANN1 is expressed in almost all Arabidopsis tissues, while the most abundant is in the root, root hairs, and in the hypocotyl epidermal cells. Annexins were also occasionally proposed to associate with cytoskeleton and vesicles, but they were never developmentally localized at the subcellular level in diverse plant tissues and organs. Using advanced light-sheet fluorescence microscopy (LSFM), we followed the developmental and subcellular localization of GFP-tagged ANN1 in post-embryonic Arabidopsis organs. By contrast to conventional microscopy, LSFM allowed long-term imaging of ANN1-GFP in Arabidopsis plants at near-environmental conditions without affecting plant viability. We studied developmental regulation of ANN1-GFP expression and localization in growing Arabidopsis roots: strong accumulation was found in the root cap and epidermal cells (preferentially in elongating trichoblasts), but it was depleted in dividing cells localized in deeper layers of the root meristem. During root hair development, ANN1-GFP accumulated at the tips of emerging and growing root hairs, which was accompanied by decreased abundance in the trichoblasts. In aerial plant parts, ANN1-GFP was localized mainly in the cortical cytoplasm of trichomes and epidermal cells of hypocotyls, cotyledons, true leaves, and their petioles. At the subcellular level, ANN1-GFP was enriched at the plasma membrane (PM) and vesicles of non-dividing cells and in mitotic and cytokinetic microtubular arrays of dividing cells. Additionally, an independent immunolocalization method confirmed ANN1-GFP association with mitotic and cytokinetic microtubules (PPBs and phragmoplasts) in dividing cells of the lateral root cap. Lattice LSFM revealed subcellular accumulation of ANN1-GFP around the nuclear envelope of elongating trichoblasts. Massive relocation and accumulation of ANN1-GFP at the PM and in Hechtian strands and reticulum in plasmolyzed cells suggest a possible osmoprotective role of ANN1-GFP during plasmolysis/deplasmolysis cycle. This study shows complex developmental and subcellular localization patterns of ANN1 in living Arabidopsis plants.

Structural and functional imaging of large and opaque plant specimens

Three- and four-dimensional imaging techniques are a prerequisite for spatially resolving the form-structure-function relationships in plants. However, choosing the right imaging method is a difficult and time-consuming process as the imaging principles, advantages and limitations, as well as the appropriate fields of application first need to be compared. The present study aims to provide an overview of three imaging methods that allow for imaging opaque, large and thick (>5 mm, up to several centimeters), hierarchically organized plant samples that can have complex geometries. We compare light microscopy of serial thin sections followed by 3D reconstruction (LMTS3D) as an optical imaging technique, micro-computed tomography (µ-CT) based on ionizing radiation, and magnetic resonance imaging (MRI) which uses the natural magnetic properties of a sample for image acquisition. We discuss the most important imaging principles, advantages, and limitations, and suggest fields of application for each imaging technique (LMTS, µ-CT, and MRI) with regard to static (at a given time; 3D) and dynamic (at different time points; quasi 4D) structural and functional plant imaging.

Single-point ACT2 gene mutation in the Arabidopsis root hair mutant der1-3 affects overall actin organization, root growth and plant development

BACKGROUND AND AIMS

The actin cytoskeleton forms a dynamic network in plant cells. A single-point mutation in the DER1 (deformed root hairs1) locus located in the sequence of ACTIN2, a gene for major actin in vegetative tissues of Arabidopsis thaliana, leads to impaired root hair development (Ringli C, Baumberger N, Diet A, Frey B, Keller B. 2002. ACTIN2 is essential for bulge site selection and tip growth during root hair development of Arabidopsis. Plant Physiology129: 1464-1472). Only root hair phenotypes have been described so far in der1 mutants, but here we demonstrate obvious aberrations in the organization of the actin cytoskeleton and overall plant development.

METHODS

Organization of the actin cytoskeleton in epidermal cells of cotyledons, hypocotyls and roots was studied qualitatively and quantitatively by live-cell imaging of transgenic lines carrying the GFP-FABD2 fusion protein and in fixed cells after phalloidin labelling. Patterns of root growth were characterized by FM4-64 vital staining, light-sheet microscopy imaging and microtubule immunolabelling. Plant phenotyping included analyses of germination, root growth and plant biomass.

KEY RESULTS

Speed of germination, plant fresh weight and total leaf area were significantly reduced in the der1-3 mutant in comparison with the C24 wild-type. Actin filaments in root, hypocotyl and cotyledon epidermal cells of the der1-3 mutant were shorter, thinner and arranged in more random orientations, while actin bundles were shorter and had altered orientations. The wavy pattern of root growth in der1-3 mutant was connected with higher frequencies of shifted cell division planes (CDPs) in root cells, which was consistent with the shifted positioning of microtubule-based preprophase bands and phragmoplasts. The organization of cortical microtubules in the root cells of the der1-3 mutant, however, was not altered.

CONCLUSIONS

Root growth rate of the der1-3 mutant is not reduced, but changes in the actin cytoskeleton organization can induce a wavy root growth pattern through deregulation of CDP orientation. The results suggest that the der1-3 mutation in the ACT2 gene does not influence solely root hair formation process, but also has more general effects on the actin cytoskeleton, plant growth and development.

Multiscale imaging of plant development by light-sheet fluorescence microscopy

Light-sheet fluorescence microscopy (LSFM) methods collectively represent the major breakthrough in developmental bio-imaging of living multicellular organisms. They are becoming a mainstream approach through the development of both commercial and custom-made LSFM platforms that are adjusted to diverse biological applications. Based on high-speed acquisition rates under conditions of low light exposure and minimal photo-damage of the biological sample, these methods provide ideal means for long-term and in-depth data acquisition during organ imaging at single-cell resolution. The introduction of LSFM methods into biology extended our understanding of pattern formation and developmental progress of multicellular organisms from embryogenesis to adult body. Moreover, LSFM imaging allowed the dynamic visualization of biological processes under almost natural conditions. Here, we review the most important, recent biological applications of LSFM methods in developmental studies of established and emerging plant model species, together with up-to-date methods of data editing and evaluation for modelling of complex biological processes. Recent applications in animal models push LSFM into the forefront of current bio-imaging approaches. Since LSFM is now the single most effective method for fast imaging of multicellular organisms, allowing quantitative analyses of their long-term development, its broader use in plant developmental biology will likely bring new insights.

Recent Progress in Light Sheet Microscopy for Biological Applications

The introduction of light sheet fluorescence microscopy (LSFM) has overcome the challenges in conventional optical microscopy. Among the recent breakthroughs in fluorescence microscopy, LSFM had been proven to provide a high three-dimensional spatial resolution, high signal-to-noise ratio, fast imaging acquisition rate, and minuscule levels of phototoxic and photodamage effects. The aforementioned auspicious properties are crucial in the biomedical and clinical research fields, covering a broad range of applications: from the super-resolution imaging of intracellular dynamics in a single cell to the high spatiotemporal resolution imaging of developmental dynamics in an entirely large organism. In this review, we provided a systematic outline of the historical development of LSFM, detailed discussion on the variants and improvements of LSFM, and delineation on the most recent technological advancements of LSFM and its potential applications in single molecule/particle detection, single-molecule super-resolution imaging, imaging intracellular dynamics of a single cell, multicellular imaging: cell-cell and cell-matrix interactions, plant developmental biology, and brain imaging and developmental biology.

Technical Review: Microscopy and Image Processing Tools to Analyze Plant Chromatin: Practical Considerations

In situ nucleus and chromatin analyses rely on microscopy imaging that benefits from versatile, efficient fluorescent probes and proteins for static or live imaging. Yet the broad choice in imaging instruments offered to the user poses orientation problems. Which imaging instrument should be used for which purpose? What are the main caveats and what are the considerations to best exploit each instrument's ability to obtain informative and high-quality images? How to infer quantitative information on chromatin or nuclear organization from microscopy images? In this review, we present an overview of common, fluorescence-based microscopy systems and discuss recently developed super-resolution microscopy systems, which are able to bridge the resolution gap between common fluorescence microscopy and electron microscopy. We briefly present their basic principles and discuss their possible applications in the field, while providing experience-based recommendations to guide the user toward best-possible imaging. In addition to raw data acquisition methods, we discuss commercial and noncommercial processing tools required for optimal image presentation and signal evaluation in two and three dimensions.

Cell and Developmental Biology of Plant Mitogen-Activated Protein Kinases

Plant mitogen-activated protein kinases (MAPKs) constitute a network of signaling cascades responsible for transducing extracellular stimuli and decoding them to dedicated cellular and developmental responses that shape the plant body. Over the last decade, we have accumulated information about how MAPK modules control the development of reproductive tissues and gametes and the embryogenic and postembryonic development of vegetative organs such as roots, root nodules, shoots, and leaves. Of key importance to understanding how MAPKs participate in developmental and environmental signaling is the characterization of their subcellular localization, their interactions with upstream signal perception mechanisms, and the means by which they target their substrates. In this review, we summarize the roles of MAPK signaling in the regulation of key plant developmental processes, and we survey what is known about the mechanisms guiding the subcellular compartmentalization of MAPK modules.

Advanced microscopy methods for bioimaging of mitotic microtubules in plants

Mitotic cell division in plants is a dynamic process playing a key role in plant morphogenesis, growth, and development. Since progress of mitosis is highly sensitive to external stresses, documentation of mitotic cell division in living plants requires fast and gentle live-cell imaging microscopy methods and suitable sample preparation procedures. This chapter describes, both theoretically and practically, currently used advanced microscopy methods for the live-cell visualization of the entire process of plant mitosis. These methods include microscopy modalities based on spinning disk, Airyscan confocal laser scanning, structured illumination, and light-sheet bioimaging of tissues or whole plant organs with diverse spatiotemporal resolution. Examples are provided from studies of mitotic cell division using microtubule molecular markers in the model plant Arabidopsis thaliana, and from deep imaging of mitotic microtubules in robust plant samples, such as legume crop species Medicago sativa.

Technical implementations of light sheet microscopy

Fluorescence-based microscopy is among the most successful methods in biological studies. It played a critical role in the visualization of subcellular structures and in the analysis of complex cellular processes, and it is nowadays commonly employed in genetic and drug screenings. Among the fluorescence-based microscopy techniques, light sheet fluorescence microscopy (LSFM) has shown a quite interesting set of benefits. The technique combines the speed of epi-fluorescence acquisition with the optical sectioning capability typical of confocal microscopes. Its unique configuration allows the excitation of only a thin plane of the sample, thus fast, high resolution imaging deep inside tissues is nowadays achievable. The low peak intensity with which the sample is illuminated diminishes phototoxic effects and decreases photobleaching of fluorophores, ensuring data collection for days with minimal adverse consequences on the sample. It is no surprise that LSFM applications have raised in just few years and the technique has been applied to study a wide variety of samples, from whole organism, to tissues, to cell clusters, and single cells. As a consequence, in recent years numerous set-ups have been developed, each one optimized for the type of sample in use and the requirements of the question at hand. Hereby, we aim to review the most advanced LSFM implementations to assist new LSFM users in the choice of the LSFM set-up that suits their needs best. We also focus on new commercial microscopes and "do-it-yourself" strategies; likewise we review recent designs that allow a swift integration of LSFM on existing microscopes.

Light Sheet Fluorescence Microscopy Optimized for Long-Term Imaging of Arabidopsis Root Development

Light sheet fluorescence microscopy (LSFM) allows sustained and repeated optical sectioning of living specimens at high spatial and temporal resolution, with minimal photodamage. Here, we describe in detail both the hardware and the software elements of a live imaging method based on LSFM and optimized for tracking and 3D scanning of Arabidopsis root tips grown vertically in physiological conditions. The system is relatively inexpensive and with minimal footprint; hence it is well suited for laboratories of any size.

Gene Expression Pattern and Protein Localization of Arabidopsis Phospholipase D Alpha 1 Revealed by Advanced Light-Sheet and Super-Resolution Microscopy

Phospholipase D alpha 1 (PLDα1, At3g15730) and its product phosphatidic acid (PA) are involved in a variety of cellular and physiological processes, such as cytoskeletal remodeling, regulation of stomatal closure and opening, as well as biotic and abiotic stress signaling. Here we aimed to study developmental expression patterns and subcellular localization of PLDα1 in Arabidopsis using advanced microscopy methods such as light-sheet fluorescence microscopy (LSFM) and structured illumination microscopy (SIM). We complemented two knockout pldα1 mutants with a YFP-tagged PLDα1 expressed under the PLDα1 native promoter in order to study developmental expression pattern and subcellular localization of PLDα1 in Arabidopsis thaliana under natural conditions. Imaging of tissue-specific and developmentally-regulated localization of YFP-tagged PLDα1 by LSFM in roots of growing seedlings showed accumulation of PLDα1-YFP in the root cap and the rhizodermis. Expression of PLDα1-YFP in the rhizodermis was considerably higher in trichoblasts before and during root hair formation and growth. Thus, PLDα1-YFP accumulated in emerging root hairs and in the tips of growing root hairs. PLDα1-YFP showed cytoplasmic subcellular localization in root cap cells and in cells of the root transition zone. In aerial parts of plants PLDα1-YFP was also localized in the cytoplasm showing enhanced accumulation in the cortical cytoplasmic layer of epidermal non-dividing cells of hypocotyls, leaves, and leaf petioles. However, in dividing cells of root apical meristem and leaf petiole epidermis PLDα1-YFP was enriched in mitotic spindles and phragmoplasts, as revealed by co-visualization with microtubules. Finally, super-resolution SIM imaging revealed association of PLDα1-YFP with both microtubules and clathrin-coated vesicles (CCVs) and pits (CCPs). In conclusion, this study shows the developmentally-controlled expression and subcellular localization of PLDα1 in dividing and non-dividing Arabidopsis cells.

Phloem differentiation: an integrative model for cell specification

Plant vasculature consists of two major conductive cell types, xylem tracheary elements and phloem sieve elements (SEs). Both cell types undergo a highly specialized differentiation process. The root meristem of Arabidopsis displays a stereotypical anatomy in which the central vasculature is surrounded by concentric layers of outer tissues. Each cell file is derived from stem cells located in the root tip. A series of formative and proliferative divisions take place in the meristem; these are followed by cell expansion and differentiation. Protophloem differentiation is unique in being complete only 20-25 cells away from the first stem cell, and during the differentiation process the cells lose several organelles, including the nucleus, while the remaining organelles are rearranged. Defects in SE development have been shown to result in impaired auxin transport and response and therefore systemically affect root growth. Although a few genes have been demonstrated to function in phloem development, detailed analyses and a comprehensive understanding of sieve element development (i.e. how often the stem cells divide, how frequently enucleation takes place, and how SE development is coordinated between cell division and differentiation on a molecular level) are still lacking. Advanced live-imaging techniques which enable prolonged time-lapse captures of root tip growth as well as single-cell transcriptomic analysis of the 20-25 cells in the SE file could help resolve these questions. In addition, understanding the interplay between the PLETHORA (PLT) gradient, which is known to govern the root zonation, and phloem development within the root meristem could shed light on the rapidity of SE differentiation and its importance to the meristem.

What Has Been Seen Cannot Be Unseen-Detecting Auxin In Vivo

Auxins mediate various processes that are involved in plant growth and development in response to specific environmental conditions. Its proper spatio-temporal distribution that is driven by polar auxin transport machinery plays a crucial role in the wide range of auxins physiological effects. Numbers of approaches have been developed to either directly or indirectly monitor auxin distribution in vivo in order to elucidate the basis of its precise regulation. Herein, we provide an updated list of valuable techniques used for monitoring auxins in plants, with their utilities and limitations. Because the spatial and temporal resolutions of the presented approaches are different, their combination may provide a comprehensive outcome of auxin distribution in diverse developmental processes.

Quantitative Reflection Imaging for the Morphology and Dynamics of Live Aplysia californica Pedal Ganglion Neurons Cultured on Nanostructured Plasmonic Crystals

We describe a reflection imaging system that consists of a plasmonic crystal, a common laboratory microscope, and band-pass filters for use in the quantitative imaging and in situ monitoring of live cells and their substrate interactions. Surface plasmon resonance (SPR) provides a highly sensitive method to monitor changes in physicochemical properties occurring at metal-dielectric interfaces. Polyelectrolyte thin films deposited using the layer-by-layer (LBL) self-assembly method provide a reference system for calibrating the reflection contrast changes that occur when the polyelectrolyte film thickness changes and provide insight into the optical responses that originate from the multiple plasmonic features supported by this imaging system. Finite-difference time-domain (FDTD) simulations of the optical responses measured experimentally from the polyelectrolyte reference system are used to provide a calibration of the optical system for subsequent use in quantitative studies investigating live cell dynamics in cultures supported on a plasmonic crystal substrate. Live Aplysia californica pedal ganglion neurons cultured in artificial seawater were used as a model system through which to explore the utility of this plasmonic imaging technique. Here, the morphology of cellular peripheral structures ≲80 nm in thickness were quantitatively analyzed, and the dynamics of their trypsin-induced surface detachment were visualized. These results illustrate the capacities of this system for use in investigations of the dynamics of ultrathin cellular structures within complex bioanalytical environments.

Push-pull strategy in the regulation of postembryonic root development

Unlike animals, plants continue to grow throughout their lives. The stem cell niche, protected in meristems of shoots and roots, enables this process. In the root, stem cells produce precursors for highly organized cell types via asymmetric cell divisions. These precursors, which are "transit-amplifying cells," actively divide for several rounds before entering into differentiation programs. In this review, we highlight positive feedback regulation between shoot- and root-ward signals during the postembryonic root growth, which is reminiscent of a "push-pull strategy" in business parlance. This property of molecular networks underlies the regulation of stem cells and their organizer, the "quiescent center," as well as of the signaling between stem cell niche, transit-amplifying cells, and beyond.

Light Sheet Fluorescence Microscopy of Plant Roots Growing on the Surface of a Gel

One of the key questions in understanding plant development is how single cells behave in a larger context of the tissue. Therefore, it requires the observation of the whole organ with a high spatial- as well as temporal resolution over prolonged periods of time, which may cause photo-toxic effects. This protocol shows a plant sample preparation method for light-sheet microscopy, which is characterized by mounting the plant vertically on the surface of a gel. The plant is mounted in such a way that the roots are submerged in a liquid medium while the leaves remain in the air. In order to ensure photosynthetic activity of the plant, a custom-made lighting system illuminates the leaves. To keep the roots in darkness the water surface is covered with sheets of black plastic foil. This method allows long-term imaging of plant organ development in standardized conditions.

Alfalfa Root Growth Rate Correlates with Progression of Microtubules during Mitosis and Cytokinesis as Revealed by Environmental Light-Sheet Microscopy

Cell division and expansion are two fundamental biological processes supporting indeterminate root growth and development of plants. Quantitative evaluations of cell divisions related to root growth analyses have been performed in several model crop and non-crop plant species, but not in important legume plant Medicago sativa. Light-sheet fluorescence microscopy (LSFM) is an advanced imaging technique widely used in animal developmental biology, providing efficient fast optical sectioning under physiological conditions with considerably reduced phototoxicity and photobleaching. Long-term 4D imaging of living plants offers advantages for developmental cell biology not available in other microscopy approaches. Recently, LSFM was implemented in plant developmental biology studies, however, it is largely restricted to the model plant Arabidopsis thaliana. Cellular and subcellular events in crop species and robust plant samples have not been studied by this method yet. Therefore we performed LSFM long-term live imaging of growing root tips of transgenic alfalfa plants expressing the fluorescent molecular marker for the microtubule-binding domain (GFP-MBD), in order to study dynamic patterns of microtubule arrays during mitotic cell division. Quantitative evaluations of cell division progress in the two root tissues (epidermis and cortex) clearly indicate that root growth rate is correlated with duration of cell division in alfalfa roots. Our results favor non-invasive environmental LSFM as one of the most suitable methods for qualitative and quantitative cellular and developmental imaging of living transgenic legume crops.

Macro optical projection tomography for large scale 3D imaging of plant structures and gene activity

Optical projection tomography (OPT) is a well-established method for visualising gene activity in plants and animals. However, a limitation of conventional OPT is that the specimen upper size limit precludes its application to larger structures. To address this problem we constructed a macro version called Macro OPT (M-OPT). We apply M-OPT to 3D live imaging of gene activity in growing whole plants and to visualise structural morphology in large optically cleared plant and insect specimens up to 60 mm tall and 45 mm deep. We also show how M-OPT can be used to image gene expression domains in 3D within fixed tissue and to visualise gene activity in 3D in clones of growing young whole Arabidopsis plants. A further application of M-OPT is to visualise plant-insect interactions. Thus M-OPT provides an effective 3D imaging platform that allows the study of gene activity, internal plant structures and plant-insect interactions at a macroscopic scale.

Multi-sample Arabidopsis Growth and Imaging Chamber (MAGIC) for long term imaging in the ZEISS Lightsheet Z.1

Time-course imaging experiments on live organisms are critical for understanding the dynamics of growth and development. Light-sheet microscopy has advanced the field of long-term imaging of live specimens by significantly reducing photo-toxicity and allowing fast acquisition of three-dimensional data over time. However, current light-sheet technology does not allow the imaging of multiple plant specimens in parallel. To achieve higher throughput, we have developed a Multi-sample Arabidopsis Growth and Imaging Chamber (MAGIC) that provides near-physiological imaging conditions and allows high-throughput time-course imaging experiments in the ZEISS Lightsheet Z.1. Here, we illustrate MAGIC's imaging capabilities by following cell divisions, as an indicator of plant growth and development, over prolonged time periods. To automatically quantify the number of cell divisions in long-term experiments, we present a FIJI-based image processing pipeline. We demonstrate that plants imaged with our chamber undergo cell divisions for >16 times longer than those with the glass capillary system supplied by the ZEISS Z1.

Developmental Nuclear Localization and Quantification of GFP-Tagged EB1c in Arabidopsis Root Using Light-Sheet Microscopy

The development of the root apex is determined by progress of cells from the meristematic region to the successive post-mitotic developmental zones for transition, cell elongation and final cell differentiation. We addressed root development, tissue architecture and root developmental zonation by means of light-sheet microscopic imaging of Arabidopsis thaliana seedlings expressing END BINDING protein 1c (EB1c) fused to green fluorescent protein (GFP) under control of native EB1c promoter. Unlike the other two members of the EB1 family, plant-specific EB1c shows prominent nuclear localization in non-dividing cells in all developmental zones of the root apex. The nuclear localization of EB1c was previously mentioned solely in meristematic cells, but not further addressed. With the help of advanced light-sheet microscopy, we report quantitative evaluations of developmentally-regulated nuclear levels of the EB1c protein tagged with GFP relatively to the nuclear size in diverse root tissues (epidermis, cortex, and endodermis) and root developmental zones (meristem, transition, and elongation zones). Our results demonstrate a high potential of light-sheet microscopy for 4D live imaging of fluorescently-labeled nuclei in complex samples such as developing roots, showing capacity to quantify parameters at deeper cell layers (e.g., endodermis) with minimal aberrations. The data presented herein further signify the unique role of developmental cell reprogramming in the transition from cell proliferation to cell differentiation in developing root apex.

Super-resolution Microscopy in Plant Cell Imaging

Although the development of super-resolution microscopy methods dates back to 1994, relevant applications in plant cell imaging only started to emerge in 2010. Since then, the principal super-resolution methods, including structured-illumination microscopy (SIM), photoactivation localization microscopy (PALM), stochastic optical reconstruction microscopy (STORM), and stimulated emission depletion microscopy (STED), have been implemented in plant cell research. However, progress has been limited due to the challenging properties of plant material. Here we summarize the basic principles of existing super-resolution methods and provide examples of applications in plant science. The limitations imposed by the nature of plant material are reviewed and the potential for future applications in plant cell imaging is highlighted.