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Measuring Extracellular Proton and Anionic Fluxes in Arabidopsis Pollen Tubes.

ABSTRACT: The ion-selective vibrating probe has been used to detect and quantify the magnitude and direction of transmembrane fluxes of several ions in a wide range of biological systems. Inherently non-invasive, vibrating probes have been essential to access relevant electrophysiological parameters related to apical growth and morphogenesis in pollen tubes, a highly specialized cell where spatiotemporal tuning of ion dynamics is fundamental. Of relevance, crucial processes to the cell physiology of pollen tubes associated with protons and anions have been elucidated using vibrating probes, allowing the identification of diverse molecular players underlying and regulating their extracellular fluxes. The use of Arabidopsis thaliana as a genetic model system posed new challenges given their relatively small dimensions and difficult manipulation in vitro. Here, we describe protocol optimizations that made the use of the ion-selective vibrating probe in Arabidopsis pollen tubes feasible, ensuring consistent and reproducible data. Quantitative methods like this enabled characterizing phenotypes of ion transporter mutants, which are not directly detectable by evident morphological and reproductive defects, providing valuable insights into molecular and cellular mechanisms. The protocol for quantifying extracellular proton and anionic fluxes detailed here can be adjusted to other systems and species, while the sample preparation can be applied to correlated techniques, facilitating the research of pollen tube growth and development.

SUBMITTER: Portes MT

PROVIDER: S-EPMC7952931 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundThe pollen tube (PT) serves as a model system for investigating plant cell growth and morphogenesis. Ultrastructural studies are indispensable to complement data from physiological and genetic analyses, yet an effective method is lacking for PTs of the model plant Arabidopsis thaliana.MethodsHere, we present reliable approaches for ultrastructural studies of Arabidopsis PTs, as well as an efficient technique for immunogold detection of cell wall epitopes. Using different fixation and embedding strategies, we show the amount of PT ultrastructural details that can be obtained by the different methods.ResultsDozens of cross-sections can be obtained simultaneously by the approach, which facilitates and shortens the time for evaluation. In addition to in vitro-grown PTs, our study follows the route of PTs from germination, growth along the pistil, to the penetration of the dense stylar tissue, which requires considerable mechanical forces. To this end, PTs have different strategies from growing between cells but also between the protoplast and the cell wall and even within each other, where they share a partly common cell wall. The separation of PT cell walls in an outer and an inner layer reported for many plant species is less clear in Arabidopsis PTs, where these cell wall substructures are connected by a distinct transition zone.ConclusionsThe major advancement of this method is the effective production of a large number of longitudinal and cross-sections that permits obtaining a detailed and representative picture of pollen tube structures in an unprecedented way. This is particularly important when comparing PTs of wild type and mutants to identify even subtle alterations in cytoarchitecture. Arabidopsis is an excellent plant for genetic manipulation, yet the PTs, several-times smaller compared to tobacco or lily, represent a technical challenge. This study reveals a method to overcome this problem and make Arabidopsis PTs more amenable to a combination of genetic and ultrastructural analyses.

Project description:BACKGROUND: Arabinogalactan proteins (AGPs) are cell wall proteoglycans that have been shown to be important for pollen development. An Arabidopsis double null mutant for two pollen-specific AGPs (agp6 agp11) showed reduced pollen tube growth and compromised response to germination cues in vivo. A microarray experiment was performed on agp6 agp11 pollen tubes to search for genetic interactions in the context of pollen tube growth. A yeast two-hybrid experiment for AGP6 and AGP11 was also designed. RESULTS: The lack of two specific AGPs induced a meaningful shift in the gene expression profile. In fact, a high number of genes showed altered expression levels, strengthening the case that AGP6 and AGP11 are involved in complex phenomena. The expression levels of calcium- and signaling-related genes were found to be altered, supporting the known roles of the respective proteins in pollen tube growth. Although the precise nature of the proposed interactions needs further investigation, the putative involvement of AGPs in signaling cascades through calmodulin and protein degradation via ubiquitin was indicated. The expression of stress-, as well as signaling- related, genes was also changed; a correlation that may result from the recognized similarities between signaling pathways in both defense and pollen tube growth.The results of yeast two-hybrid experiments lent further support to these signaling pathways and revealed putative AGP6 and AGP11 interactors implicated in recycling of cell membrane components via endocytosis, through clathrin-mediated endosomes and multivesicular bodies. CONCLUSIONS: The data presented suggest the involvement of AGP6 and AGP11 in multiple signaling pathways, in particular those involved in developmental processes such as endocytosis-mediated plasma membrane remodeling during Arabidopsis pollen development. This highlights the importance of endosomal trafficking pathways which are rapidly emerging as fundamental regulators of the wall physiology.

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Measuring Extracellular Proton and Anionic Fluxes in Arabidopsis Pollen Tubes.

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