Plant cell electrophysiology: Applications in growth enhancement, somatic hybridisation and gene transfer

Integrated flow cytometric and proteomics analyses reveal the regulatory network underlying sugarcane protoplast responses to fusion

BACKGROUND

Somatic cell fusion is a process that transfers cytoplasmic and nuclear genes to create new germplasm resources. But our limited understanding of the physiological and molecular mechanisms that shape protoplast responses to fusion.

METHOD

We employed flow cytometry, cytology, proteomics, and gene expression analysis to examine the sugarcane (Saccharum spp.) protoplast fusion.

RESULTS

Flow cytometry analysis revealed the fusion rate of protoplasts was 1.95%, the FSC value and SSC of heterozygous cells was 1.17-1.47 times higher than that of protoplasts. The protoplasts viability decreased and the MDA increased after fusion. During fusion, the cell membranes were perforated to different degrees, nuclear activity was weakened, while microtubules depolymerized and formed several short rod like structures in the protoplasts. The most abundant proteins during fusion were mainly involved in RNA processing and modification, cell cycle control, cell division, chromosome partition, nuclear structure, extracellular structures, and nucleotide transport and metabolism. Moreover, the expression of key regeneration genes, such as WUS, GAUT, CESA, PSK, Aux/IAA, Cdc2, Cyclin D3, Cyclin A, and Cyclin B, was significantly altered following fusion.

PURPOSE AND SIGNIFICANCE

Overall, our findings provide a theoretical basis that increases our knowledge of the mechanisms underlying protoplast fusion.

Passive Recording of Bioelectrical Signals from Non-Excitable Cells by Fluorescent Mirroring

Bioelectrical variations trigger different cell responses, including migration, mitosis, and mutation. At the tissue level, these actions result in phenomena such as wound healing, proliferation, and pathogenesis. Monitoring these mechanisms dynamically is highly desirable in diagnostics and drug testing. However, existing technologies are invasive: either they require physical access to the intracellular compartments, or they imply direct contact with the cellular medium. Here, we present a novel approach for the passive recording of electrical signals from non-excitable cells adhering to 3D microelectrodes, based on optical mirroring. Preliminary results yielded a fluorescence intensity output increase of the 5,8% in the presence of a HEK-293 cell on the electrode compared to bare microelectrodes. At present, this technology may be employed to evaluate cell-substrate adhesion and monitor cell proliferation. Further refinements could allow extrapolating quantitative data on surface charges and resting potential to investigate the electrical phenomena involved in cell migration and cancer progression.

Real-time detection of somatic hybrid cells during electrofusion of carrot protoplasts with stably labelled mitochondria

Somatic hybridisation in the carrot, as in other plant species, enables the development of novel plants with unique characteristics. This process can be induced by the application of electric current to isolated protoplasts, but such electrofusion requires an effective hybrid cell identification method. This paper describes the non-toxic fluorescent protein (FP) tagging of protoplasts which allows discrimination of fusion components and identification of hybrids in real-time during electrofusion. One of four FPs: cyan (eCFP), green (sGFP), yellow (eYFP) or the mCherry variant of red FP (RFP), with a fused mitochondrial targeting sequence, was introduced to carrot cell lines of three varieties using Agrobacterium-mediated transformation. After selection, a set of carrot callus lines with either GFP, YFP or RFP-labelled mitochondria that showed stable fluorescence served as protoplast sources. Various combinations of direct current (DC) parameters on protoplast integrity and their ability to form hybrid cells were assessed during electrofusion. The protoplast response and hybrid cell formation depended on DC voltage and pulse time, and varied among protoplast sources. Heterofusants (GFP + RFP or YFP + RFP) were identified by detection of a dual-colour fluorescence. This approach enabled, for the first time, a comprehensive assessment of the carrot protoplast response to the applied electric field conditions as well as identification of the DC parameters suitable for hybrid formation, and an estimation of the electrofusion success rate by performing real-time observations of protoplast fluorescence.

From Stress to Embryos: Some of the Problems for Induction and Maturation of Somatic Embryos

Although somatic embryogenesis has been successfully achieved in numerous plant species, little is known about the mechanism(s) underlying this process. Changes in the balance of growth regulators of the culture medium, osmolarity, or amino acids as well as the genotype and developmental stage of the tissue used as initial explant may have a pivotal influence on the induction of somatic embryogenic cultures. Moreover, different stress agents (ethylene, activated charcoal, cold or heat or electrical shocks), as well as abscisic acid, can also foster the induction or further development of somatic embryos. In the process, cells first return to a stem cell-like status and then either enter their new program or dye when the stress level exceeds cell tolerance. Recalcitrance to differentiation of somatic cells into embryos is frequently observed, and problems such as secondary or recurrent embryogenesis, embryo growth arrest (at the globular stage or during the transition from torpedo to cotyledonary stage), and development of only the aerial part of somatic embryos can appear, interfering with normal germination and conversion of embryos to plants. Some solutions to solve these problems associated to embryogenesis are proposed and two very efficient somatic embryogenesis protocols for two model plant species are detailed.

Role of early signalling events in plant-insect interactions

The response of plants to the stress caused by herbivores involves several different defence mechanisms. These responses begin at the plant cell plasma membrane, where insect herbivores interact physically by causing mechanical damage and chemically by introducing elicitors or by triggering plant-derived signalling molecules. The earliest plant responses to herbivore contact are represented by ion flux unbalances generated in the plant cell plasma membrane at the damaged site. Differences in the charge distribution generate plasma transmembrane potential (V m) variation, the first event, which eventually leads to the initiation of signal transduction pathways and gene expression. Calcium signalling and the generation of reactive oxygen and nitrogen species are early events closely related to V m variations. This review provides an update on recent developments and advances in plant early signalling in response to herbivory, with particular emphasis on the electrophysiological variations of the plasma membrane potential, calcium signalling, cation channel activity, production of reactive oxygen and nitrogen species, and formation of a systemically moving signal from wounded tissues. The roles of calcium-dependent protein kinases and calcineurin signalling are also discussed.