FLUORESCENCE MICROSCOPY OF LIVING PLANT 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.

Light Sheet Fluorescence Microscopy Quantifies Calcium Oscillations in Root Hairs of Arabidopsis thaliana

Calcium oscillations play a role in the regulation of the development of tip-growing plant cells. Using optical microscopy, calcium oscillations have been observed in a few systems (e.g. pollen tubes, fungal hyphae and algal rhizoids). High-resolution, non-phototoxic and rapid imaging methods are required to study the calcium oscillation in root hairs. We show that light sheet fluorescence microscopy is optimal to image growing root hairs of Arabidopsis thaliana and to follow their oscillatory tip-focused calcium gradient. We describe a protocol for performing live imaging of root hairs in seedlings expressing the cytosol-localized ratiometric calcium indicator Yellow Cameleon 3.6. Using this protocol, we measured the calcium gradient in a large number of root hairs. We characterized their calcium oscillations and correlated them with the rate of hair growth. The method was then used to screen the effect of auxin on the properties of the growing root hairs.

Calcium improves apoplastic-cytosolic ion homeostasis in salt-stressed Vicia faba leaves

Salinity disturbs both apoplastic and cytosolic Ca2+ and pH ([Ca2+]apo, [Ca2+]cyt, pHapo and pHcyt) homeostasis, and decreases plant growth. Seedlings of Vicia faba L. cv. Fuego were cultivated in hydroponics for 7 days under control, salinity (S), extra Ca (Ca) or salinity with extra Ca (S+Ca) conditions. The [Ca2+]apo, and pHapo in the leaves were then recorded in parallel by a pseudoratiometric method, described here for the first time. Lower [Ca2+]apo and higher pHapo were obtained under salinity, whereas extra Ca supply increased the [Ca2+]apo and acidified the pHapo. Moreover, the ratiometric imaging recorded that [Ca2+]cyt and pHcyt were highest in S+Ca plants and lowest in control plants. After all pretreatments, direct addition of NaC6H11O7 to leaves induced a decrease in [Ca2+]apo in control and S+Ca plants, but not in S and Ca plants, and only slightly affected pHapo. Addition of NaCl increased [Ca2+]cyt in protoplasts from all plants but only transiently in protoplasts from S+Ca plants. Addition of NaCl decreased pHcyt in protoplasts from Ca-pretreated plants. We conclude that Ca supply improves both apoplastic and cytosolic ion homeostasis. In addition, NaC6H11O7 probably causes transport of Ca from the apoplast into the cytosol, thereby leading to a higher resting [Ca2+]cyt.

Microtubules in Plant Cells: Strategies and Methods for Immunofluorescence, Transmission Electron Microscopy, and Live Cell Imaging

Microtubules (MTs) are required throughout plant development for a wide variety of processes, and different strategies have evolved to visualize and analyze them. This chapter provides specific methods that can be used to analyze microtubule organization and dynamic properties in plant systems and summarizes the advantages and limitations for each technique. We outline basic methods for preparing samples for immunofluorescence labeling, including an enzyme-based permeabilization method, and a freeze-shattering method, which generates microfractures in the cell wall to provide antibodies access to cells in cuticle-laden aerial organs such as leaves. We discuss current options for live cell imaging of MTs with fluorescently tagged proteins (FPs), and provide chemical fixation, high-pressure freezing/freeze substitution, and post-fixation staining protocols for preserving MTs for transmission electron microscopy and tomography.

Bacterially produced Pt-GFP as ratiometric dual-excitation sensor for in planta mapping of leaf apoplastic pH in intact Avena sativa and Vicia faba

BACKGROUND

Ratiometric analysis with H(+)-sensitive fluorescent sensors is a suitable approach for monitoring apoplastic pH dynamics. For the acidic range, the acidotropic dual-excitation dye Oregon Green 488 is an excellent pH sensor. Long lasting (hours) recordings of apoplastic pH in the near neutral range, however, are more problematic because suitable pH indicators that combine a good pH responsiveness at a near neutral pH with a high photostability are lacking. The fluorescent pH reporter protein from Ptilosarcus gurneyi (Pt-GFP) comprises both properties. But, as a genetically encoded indicator and expressed by the plant itself, it can be used almost exclusively in readily transformed plants. In this study we present a novel approach and use purified recombinant indicators for measuring ion concentrations in the apoplast of crop plants such as Vicia faba L. and Avena sativa L.

RESULTS

Pt-GFP was purified using a bacterial expression system and subsequently loaded through stomata into the leaf apoplast of intact plants. Imaging verified the apoplastic localization of Pt-GFP and excluded its presence in the symplast. The pH-dependent emission signal stood out clearly from the background. PtGFP is highly photostable, allowing ratiometric measurements over hours. By using this approach, a chloride-induced alkalinizations of the apoplast was demonstrated for the first in oat.

CONCLUSIONS

Pt-GFP appears to be an excellent sensor for the quantification of leaf apoplastic pH in the neutral range. The presented approach encourages to also use other genetically encoded biosensors for spatiotemporal mapping of apoplastic ion dynamics.

Multiphoton imaging of freezing and heating effects in plant leaves

Thermally-induced changes in Arabidopsis thaliana leaves were investigated with a novel cryo microscope by multiphoton, fluorescence lifetime and spectral imaging as well as micro spectroscopy. Samples were excited with fs pulses in the near-infrared range and cooled/heated in a cryogenic chamber. The results show morphological changes in the chloroplast distribution as well as a shift from chlorophyll to cell-wall fluorescence with decreasing temperature. At temperatures below -40 °C, also second harmonic generation was observed. The measurements illustrate the suitability of multiphoton imaging to investigate thermally-induced changes at temperatures used for cryopreservation as well as for basic investigations of thermal effects on plant tissue in general.

High-resolution imaging of Ca2+ , redox status, ROS and pH using GFP biosensors

Many plant response systems are linked to complex dynamics in signaling molecules such as Ca(2+) and reactive oxygen species (ROS) and to pH. Regulatory changes in these molecules can occur in the timeframe of seconds and are often limited to specific subcellular locales. Thus, to understand how Ca(2+) , ROS and pH form part of plants' regulatory networks, it is essential to capture their rapid dynamics with resolutions that span the whole plant to subcellular dimensions. Defining the spatio-temporal signaling 'signatures' of these regulators at high resolution has now been greatly facilitated by the generation of plants expressing a range of GFP-based bioprobes. For Ca(2+) and pH, probes such as the yellow cameleon Ca(2+) sensors (principally YC2.1 and 3.6) or the pHluorin and H148D pH sensors provide a robust suite of tools to image changes in these ions. For ROS, the tools are much more limited, with the GFP-based H(2) O(2) sensor Hyper representing a significant advance for the field. However, with this probe, its marked pH sensitivity provides a key challenge to interpretation without using appropriate controls to test for potentially coupled pH-dependent changes. Most of these Ca(2+) -, ROS- and pH-imaging biosensors are compatible with the standard configurations of confocal microscopes available to many researchers. These probes therefore represent a readily accessible toolkit to monitor cellular signaling. Their use does require appreciation of a minimal set of controls but these are largely related to ensuring that neither the probe itself nor the imaging conditions used perturb the biology of the plant under study.

Transient alkalinization in the leaf apoplast of Vicia faba L. depends on NaCl stress intensity: an in situ ratio imaging study

The apoplast is suggested to be involved not only in the response, but also in the perception and transduction of various environmental signals. In this context, apoplastic alkalinization has previously been discussed as a general stress factor caused by abiotic and biotic stress events. In this study, an ion-sensitive fluorescence probe in combination with inverted fluorescence microscopy has been used for in planta monitoring of apoplastic shoot pH during challenging of Vicia faba L. plants by NaCl stress encountered at the roots. We demonstrate that transient increases in leaf apoplastic pH are dependent on the NaCl stress intensity. Moreover, we have visualized spatial pH gradients within the leaf apoplast. Our results indicate that these pH responses are propagated from root to leaf and that this occurs along the apoplast.

Real-Time Imaging of Leaf Apoplastic pH Dynamics in Response to NaCl Stress

Knowledge concerning apoplastic ion concentrations is important for the understanding of many processes in plant physiology. Ion-sensitive fluorescent probes in combination with quantitative imaging techniques offer opportunities to localize, visualize, and quantify apoplastic ion dynamics in situ. The application of this technique to the leaf apoplast is complicated because of problems associated with dye loading. We demonstrate a more sophisticated dye loading procedure that enables the mapping of spatial apoplastic ion gradients over a period of 3 h. The new technique has been used for the real-time monitoring of pH dynamics within the leaf apoplast in response to NaCl stress encountered by the roots.

Strategies for imaging microtubules in plant cells

Microtubules are required throughout plant development for a wide variety of processes, and different strategies have been evolved to visualize them. This chapter summarizes the most effective of these methods and points out potential problems and pitfalls. We outline the freeze-shattering method for immunolabeling microtubules in aerial organs such as leaves that require mechanical permeabilization, discuss current options for live cell imaging of MTs with fluorescently tagged proteins (FPs), and provide different fixation protocols for preserving MTs for transmission electron microscopy including chemical fixation, high pressure freezing/freeze substitution, and post-fixation staining procedures for transmission electron microscopy.

Optical microscopy in photosynthesis

Emerging as well as the most frequently used optical microscopy techniques are reviewed and image contrast generation methods in a microscope are presented, focusing on the nonlinear contrasts such as harmonic generation and multiphoton excitation fluorescence. Nonlinear microscopy presents numerous advantages over linear microscopy techniques including improved deep tissue imaging, optical sectioning, and imaging of live unstained samples. Nonetheless, with the exception of multiphoton excitation fluorescence, nonlinear microscopy is in its infancy, lacking protocols, users and applications; hence, this review focuses on the potential of nonlinear microscopy for studying photosynthetic organisms. Examples of nonlinear microscopic imaging are presented including isolated light-harvesting antenna complexes from higher plants, starch granules, chloroplasts, unicellular alga Chlamydomonas reinhardtii, and cyanobacteria Leptolyngbya sp. and Anabaena sp. While focusing on nonlinear microscopy techniques, second and third harmonic generation and multiphoton excitation fluorescence microscopy, other emerging nonlinear imaging modalities are described and several linear optical microscopy techniques are reviewed in order to clearly describe their capabilities and to highlight the advantages of nonlinear microscopy.

Stringent control of cytoplasmic Ca2+ in guard cells of intact plants compared to their counterparts in epidermal strips or guard cell protoplasts

Cytoplasmic calcium elevations, transients, and oscillations are thought to encode information that triggers a variety of physiological responses in plant cells. Yet Ca(2+) signals induced by a single stimulus vary, depending on the physiological state of the cell and experimental conditions. We compared Ca(2+) homeostasis and stimulus-induced Ca(2+) signals in guard cells of intact plants, epidermal strips, and isolated protoplasts. Single-cell ratiometric imaging with the Ca(2+)-sensitive dye Fura 2 was applied in combination with electrophysiological recordings. Guard cell protoplasts were loaded with Fura 2 via a patch pipette, revealing a cytoplasmic free Ca(2+) concentration of around 80 nM at -47 mV. Upon hyperpolarization of the plasma membrane to -107 mV, the Ca(2+) concentration increased to levels exceeding 400 nM. Intact guard cells were able to maintain much lower cytoplasmic free Ca(2+) concentrations at hyperpolarized potentials, the average concentration at -100 mV was 183 and 90 nM in epidermal strips and intact plants, respectively. Further hyperpolarization of the plasma membrane to -160 mV induced a sustained rise of the guard cell cytoplasmic Ca(2+) concentration, which slowly returned to the prestimulus level in intact plants but not in epidermal strips. Our results show that cytoplasmic Ca(2+) concentrations are stringently controlled in guard cells of intact plants but become increasingly more sensitive to changes in the plasma membrane potential in epidermal strips and isolated protoplasts.

Variability and application of the chlorophyll fluorescence emission ratio red/far-red of leaves

Various approaches to understand and make use of the variable chlorophyll (Chl) fluorescence emission spectrum and fluorescence ratio are reviewed. The Chl fluorescence of leaves consists of two maxima in the red (near 685-690 nm), and far-red region (near 730-740 nm). The intensity and shape of the Chl fluorescence emission spectrum of leaves at room temperature are primarily dependent on the concentration of the fluorophore Chl a, and to a lower degree also on the leaf structure, the photosynthetic activity, and the leaf's optical properties. The latter determine the penetration of excitation light into the leaf as well as the emission of Chl fluorescence from different depths of the leaf. Due to the re-absorption mainly of the red Chl fluorescence band emitted inside the leaf, the ratio between the red and the far-red Chl fluorescence maxima (near 690 and 730-740 nm, respectively), e.g., as F690/F735, decreases with increasing Chl content in a curvilinear relationship and is a good inverse indicator of the Chl content of the leaf tissue, e.g., before and after stress events. The Chl fluorescence ratio of leaves can be applied for Chl determinations in basic photosynthesis research, agriculture, horticulture, and forestry. It can be used to assess changes of the photosynthetic apparatus, developmental processes of leaves, state of health, stress events, stress tolerance, and also to detect diseases or N-deficiency of plants.

Imaging the live plant cell

Observing a biological event as it unfolds in the living cell provides unique insight into the nature of the phenomenon under study. Capturing live cell data differs from imaging fixed preparations because living plants respond to the intense light used in the imaging process. In addition, live plant cells are inherently thick specimens containing colored and fluorescent molecules often removed when the plant is fixed and sectioned. For fixed cells, the straightforward goal is to maximize contrast and resolution. For live cell imaging, maximizing contrast and resolution will probably damage the specimen or rapidly bleach the probe. Therefore, the goals are different. Live cell imaging seeks a balance between image quality and the information content that comes with increasing contrast and resolution. That "lousy" live cell image may contain all the information needed to answer the question being posed--provided the investigator properly framed the question and imaged the cells appropriately. Successful data collection from live cells requires developing a specimen-mounting protocol, careful selection and alignment of microscope components, and a clear understanding of how the microscope system generates contrast and resolution. This paper discusses general aspects of modern live cell imaging and the special considerations for imaging live plant specimens.

Europium uptake and partitioning in oat (Avena sativa) roots as studied by laser-induced fluorescence spectroscopy and confocal microscopy profiling technique

The uptake of Eu3+ by elongating oat roots was studied by fluorescence spectroscopy, fluorescence lifetime measurement, and a laser excitation time-resolved confocal fluorescence profiling technique. The results of this work indicated that initial uptake of Eu3+ was highest within the undifferentiated cells of the root tip just behind the root cap, a region of maximal cell growth and differentiation and with incomplete formation of the Casparian strip around the central vascular cylinder. Distribution of assimilated Eu3+ within the root's differentiation and elongation zone was nonuniform. Higher concentrations of Eu3+ were observed within the vascular cylinder, specifically in the phloem and developing xylem parenchyma. Elevated levels of the metal were also observed in the root hairs of the mature root zone. Fluorescence spectroscopic characteristics of the assimilated Eu3+ suggested that the Eu3+ exists as inner-sphere mononuclear complexes inside the root. This work also demonstrated the effectiveness of a time-resolved Eu3+ fluorescence spectroscopy and confocal fluorescence profiling techniques for the in vivo, real-time study of metal [Eu3+] accumulation by a functioning intact plant root. This approach can prove valuable for basic and applied studies in plant nutrition and environmental uptake of actinide radionuclides.

Role of dynamics of intracellular calcium in aluminium-toxicity syndrome

This review is concentrating on the role of aluminium (Al)-calcium (Ca) interactions in Al toxicity syndrome in plants. Disruption of cytoplasmic Ca²⁺ homeostasis has been suggested as a primary trigger of Al toxicity. Aluminium causes an increase in cytosolic Ca²⁺ activity, potentially disrupting numerous biochemical and physiological processes, including those involved in the root growth. The source of Ca²⁺ for the increase in cytosolic Ca²⁺ activity under Al exposure is partly extracellular (likely to be due to the Al-resistant portion of the flux through depolarization-activated Ca²⁺ channels and fluxes through Ca²⁺ -permeable nonselective cation channels in the plasma membrane) as well as intracellular (increased cytosolic Ca²⁺ activity enhances the activity of Ca²⁺ release channels in the tonoplast and the endoplasmic reticulum membrane). The effect on increased cytosolic Ca²⁺ activity of possible Al-related inhibition of the plasma membrane and endo-membrane Ca²⁺ -ATPases and Ca²⁺ exchangers (CaX) that sequester Ca²⁺ out of the cytosol is insufficiently documented at present. The relationship between Al toxicity, cytoplasmic Ca²⁺ homeostasis and cytoplasmic pH needs to be elucidated. Technical improvements that would allow measurements of cytosolic Ca²⁺ activity within the short time after exposure to Al (seconds or shorter) are eagerly awaited. Contents I. Introduction 296 II. Symptoms of aluminium toxicity 296 III. Calcium - aluminium interactions 297 IV. The role of electrical properties of the plasma membrane in calcium-aluminium interactions 306 V. Oxidative stress 307 VI. Callose 308 VII. Cytoskeleton 308 VIII. Conclusions 309 Acknowledgements 309 References 309.

Preparation and applications of Arabidopsis thaliana guard cell protoplasts

•  Guard cells play an important role in the physiology and development of plants. The genetic resources available for Arabidopsis thaliana make it the most favorable plant species for the study of guard cell processes, but it is not easy to isolate highly purified preparations of large numbers of guard cells from this species. Here, we describe methods for isolation of both guard cell and mesophyll cell protoplasts from A. thaliana and their use in the study of unique biochemical and cellular properties of these cell types. •  Protocols developed for large- and small-scale preparation of guard cell protoplasts and mesophyll cell protoplasts are described, followed by specific examples of their use in electrophysiological, biochemical and molecular approaches such as patch clamping, enzyme assays, and reverse-transcription polymerase chain reaction. •  The protocols described yield millions of highly purified, viable guard cell protoplasts and mesophyll cell protoplasts from A. thaliana. These protoplasts have been used successfully in the study of ion channel properties, assay of ABA activation in phospholipase D activity and comparisons of gene and protein expression levels. •  These techniques make it possible to elucidate electrophysiological, biochemical and molecular genetic pathways of guard cell function.

Seeing is believing: imaging techniques to monitor plant health

Historically, early stress-induced changes in plants have been mainly detected after destructive sampling followed by biochemical and molecular determinations. Imaging techniques that allow immediate detection of stress-situations, before visual symptoms appear and adverse effects become established, are emerging as promising tools for crop yield management. Such monitoring approaches can also be applied to screen plant populations for mutants with increased stress tolerance. At the laboratory scale, different imaging methods can be tested and one or a combination best suited for crop surveillance chosen. The system of choice can be applied under controlled laboratory conditions to guide selective sampling for the molecular characterisation of rapid stress-induced changes. Such an approach permits to isolate presymptomatically induced genes, or to obtain a panoramic view of early gene expression using gene-arrays when plants undergo physiological changes undetected by the human eye. Using this knowledge, plants can be engineered to be more stress resistant, and tested for field performance by the same methodologies. In ongoing efforts of genome characterisation, genes of unknown function are revealed at an ever-accelerating pace. By monitoring changes in phenotypic characteristics of transgenic plants expressing those genes, imaging techniques could help to identify their function.

Advances in Imaging the Cell Biology of Plant-Microbe Interactions

All plant-microbe interactions are initiated at the level of the cell. Recently, the light microscope has increased in popularity as an investigative tool in plant cell biology, in part because of the parallel developments of confocal laser scanning and video microscopy, computerized image processing, and an ever-increasing array of fluorescent probes that can be applied to living cells. In addition, transgenic plants and cells can be generated in which specific components are fluorescently labeled without any invasive experimental manipulation. The application of such techniques to plant-microbe interactions has revealed microbe-induced changes in cytosolic calcium levels, the visualization of reactive oxygen species generation, cytoskeleton rearrangements, DNA cleavage, and the detailed resolution of intercellular and intracellular trafficking of viral components. These techniques, integrated with electron microscopy, molecular genetics, and other types of investigations, are likely to play an increasingly important role in future studies of plant responses to microbial pathogens or mutualists.

Aluminum accumulation at nuclei of cells in the root tip. Fluorescence detection using lumogallion and confocal laser scanning microscopy

The mechanistic basis for Al toxicity effects on root growth is still a matter of speculation, but it almost certainly involves decreased cell division at the root apex. In this series of experiments, we attempt to determine whether Al enters meristematic cells and binds to nuclei when roots are exposed to a low Al(3+) activity in solution. The methodology involved the use of the Al-sensitive stain lumogallion (3-[2,4 dihydroxyphenylazo]-2-hydroxy-5-chlorobenzene sulfonic acid), the DNA stain 4',6-diamino-phenylindole, and confocal laser scanning microscopy. Soybean (Glycine max L. Merr.) cv Young (Al-sensitive) and PI 416937 (Al-tolerant) genotypes were exposed to 1.45 microM Al(3+) for periods ranging from 30 min to 72 h, and then washed with 10 mM citrate to remove apoplastic Al. Fluorescence images show that within 30 min Al entered cells of the sensitive genotype and accumulated at nuclei in the meristematic region of the root tip. Substantial Al also was present at the cell periphery. The images indicated that the Al-tolerant genotype accumulated lower amounts of Al in meristematic and differentiating cells of the root tip and their cell walls. Collectively, the results support an important role for exclusion in Al tolerance.

Confocal laser scanning microscopy of calcium dynamics in living cells

Confocal laser scanning microscopy (CLSM) is widely used to monitor intracellular calcium levels in living cells loaded with calcium-sensitive fluorophores. This review examines the basic advantages and limitations of CLSM in in vivo imaging analyses of calcium dynamics. The benefits of utilizing ratioed images and dextran-conjugated fluorophores are addressed, and practical aspects of handling confocal datasets are outlined. After considering some relatively new microscopical methods that can be used in conjunction with conventional CLSM, possible future applications of confocal techniques in analyses of intracellular calcium dynamics are discussed.

Advances in cell separation: recent developments in counterflow centrifugal elutriation and continuous flow cell separation

Cell separation by counterflow centrifugal elutriation (CCE) or free flow electrophoresis (FFE) is performed at lower frequency than cell cloning and antibody-dependent, magnetic or fluorescence-activated cell sorting. Nevertheless, numerous recent publications confirmed that these physical cell separation methods that do not include cell labeling or cell transformation steps, may be most useful for some applications. CCE and FFE have proved to be valuable tools, if homogeneous populations of normal healthy untransformed cells are required for answering scientific questions or for clinical transplantation and cells cannot be labeled by antibodies, because suitable antibodies are not available or because antibody binding to a cell surface would induce the cell reaction which should be investigated on purified cells or because antibodies bound to the surface hamper the use of the isolated cells. In addition, the methods are helpful for studying the biological reasons for, or effects of, changes in cell size and cellular negative surface charge density. Although the value of the methods was confirmed in recent years by a considerable number of important scientific results, activities to further develop and improve the instruments have, unfortunately, declined.

Mitochondrial contribution to the anoxic Ca2+ signal in maize suspension-cultured cells

Anoxia induces a rapid elevation of the cytosolic Ca2+ concentration ([Ca2+]cyt) in maize (Zea mays L.) cells, which is caused by the release of the ion from intracellular stores. This anoxic Ca2+ release is important for gene activation and survival in O2-deprived maize seedlings and cells. In this study we examined the contribution of mitochondrial Ca2+ to the anoxic [Ca2+]cyt elevation in maize cells. Imaging of intramitochondrial Ca2+ levels showed that a majority of mitochondria released their Ca2+ in response to anoxia and took up Ca2+ upon reoxygenation. We also investigated whether the mitochondrial Ca2+ release contributed to the increase in [Ca2+]cyt under anoxia. Analysis of the spatial association between anoxic [Ca2+]cyt changes and the distribution of mitochondrial and other intracellular Ca2+ stores revealed that the largest [Ca2+]cyt increases occurred close to mitochondria and away from the tonoplast. In addition, carbonylcyanide p-trifluoromethoxyphenyl hydrazone treatment depolarized mitochondria and caused a mild elevation of [Ca2+]cyt under aerobic conditions but prevented a [Ca2+]cyt increase in response to a subsequent anoxic pulse. These results suggest that mitochondria play an important role in the anoxic elevation of [Ca2+]cyt and participate in the signaling of O2 deprivation.

Calcium imaging: a primer for mycologists

This article aims to encourage more fungal biologists to consider the imaging of cytoplasmic Ca2+ fluxes. Compared to other organisms, for fungi there have been remarkably few attempts to characterize the role of Ca2+ fluxes in signal transduction and general cellular activities, even though other approaches indicate that fungal growth and development are highly dependent upon Ca2+. The methodologies for imaging Ca2+ fluxes continue to develop rapidly. These methodologies are explained here in a style that should be accessible to a newcomer to the field, hopefully forming a bridge to the more complex methodological literature.