Simultaneous visualization of callose deposition and plasma membrane for live-cell imaging in plants

Targeted and Long-Term Fluorescence Imaging of Plant Cytomembranes Using Main-Chain Charged Polyelectrolytes with Aggregation-Induced Emission

Fluorescent polyelectrolytes have attracted tremendous attention due to their unique properties and wide applications. However, current research objects of fluorescent polyelectrolytes mainly focus on side-chain charged polyelectrolytes, and the applications of polyelectrolytes in plant cytomembrane imaging with long time and high specificity still remain challenging. Herein, long-time and targeted fluorescence imaging of plant cytomembranes was achieved for the first time using main-chain charged polyelectrolytes (MCCPs) with aggregation-induced emission (AIE). A series of MCCPs were designed and synthesized, among which the red-emissive and AIE-active MCCP with a triphenylamine linker and a cyano group around the cationic ring-fused heterocyclic core showed the best fluorescence imaging performance of plant cells. Unlike other MCCPs and its neutral form of polymer, this cyano-substituted conjugated polyelectrolyte can specifically target the cytomembrane of plant cells within a short staining time with many advantages, including wash-free staining, high photostability and imaging integrity, excellent durability (at least 12 h), and low biotoxicity. In addition to onion epidermal cells, this AIE fluorescence probe also shows good imaging capabilities for other kinds of plant cells such as Glycine max and Vigna radiata. Such an AIE-active MCCP-based imaging system provides an effective design strategy to develop fluorescence probes with high specificity and long-term imaging ability toward plant plasma membranes.

Long-term spatiotemporal and highly specific imaging of the plasma membrane of diverse plant cells using a near-infrared AIE probe

Fluorescent probes are valuable tools to visualize plasma membranes intuitively and clearly and their related physiological processes in a spatiotemporal manner. However, most existing probes have only realized the specific staining of the plasma membranes of animal/human cells within a very short time period, while almost no fluorescent probes have been developed for the long-term imaging of the plasma membranes of plant cells. Herein, we designed an AIE-active probe with NIR emission to achieve four-dimensional spatiotemporal imaging of the plasma membranes of plant cells based on a collaboration approach involving multiple strategies, demonstrated long-term real-time monitoring of morphological changes of plasma membranes for the first time, and further proved its wide applicability to plant cells of different types and diverse plant species. In the design concept, three effective strategies including the similarity and intermiscibility principle, antipermeability strategy and strong electrostatic interactions were combined to allow the probe to specifically target and anchor the plasma membrane for an ultralong amount of time on the premise of guaranteeing its sufficiently high aqueous solubility. The designed APMem-1 can quickly penetrate cell walls to specifically stain the plasma membranes of all plant cells in a very short time with advanced features (ultrafast staining, wash-free, and desirable biocompatibility) and the probe shows excellent plasma membrane specificity without staining other areas of the cell in comparison to commercial FM dyes. The longest imaging time of APMem-1 can be up to 10 h with comparable performance in both imaging contrast and imaging integrity. The validation experiments on different types of plant cells and diverse plants convincingly proved the universality of APMem-1. The development of plasma membrane probes with four-dimensional spatial and ultralong-term imaging ability provides a valuable tool to monitor the dynamic processes of plasma membrane-related events in an intuitive and real-time manner.