Raman imaging of Micrasterias: new insights into shape formation

Abstract

The algae Micrasterias with its star-shaped cell pattern is a perfect unicellular model system to study morphogenesis. How the indentations are formed in the primary cell wall at exactly defined areas puzzled scientists for decades, and they searched for chemical differences in the primary wall of the extending tips compared to the resting indents. We now tackled the question by Raman imaging and scanned in situ Micrasterias cells at different stages of development. Thousands of Raman spectra were acquired from the mother cell and the developing semicell to calculate chemical images based on an algorithm finding the most different Raman spectra. Each of those spectra had characteristic Raman bands, which were assigned to molecular vibrations of BaSO4, proteins, lipids, starch, and plant cell wall carbohydrates. Visualizing the cell wall carbohydrates revealed a cell wall thickening at the indentations of the primary cell wall of the growing semicell and uniplanar orientation of the cellulose microfibrils to the cell surface in the secondary cell wall. Crystalline cellulose dominated in the secondary cell wall spectra, while in the primary cell wall spectra, also xyloglucan and pectin were reflected. Spectral differences between the indent and tip region of the primary cell wall were scarce, but a spectral mixing approach pointed to more cellulose fibrils deposited in the indent region. Therefore, we suggest that cell wall thickening together with a denser network of cellulose microfibrils stiffens the cell wall at the indent and induces different cell wall extensibility to shape the lobes.

Interplay between the microalgae Micrasterias radians and its symbiont Dyadobacter sp. HH091

“…Furthermore, ROS, such as superoxide (O 2 − ), hydrogen peroxide (H 2 O 2 ), and hydroxyl radical (•OH), are thought to be produced as antibacterial agents and involved in oxidation or reduction of necessary or toxic metals ( Palenik et al, 1987 ). Former investigation of microalga Micrasterias spp., demonstrated that ROS are constantly generated as by-products of general metabolic cellular pathways and can be over-produced in response to stress ( Darehshouri and Lütz-Meindl, 2010 ; Lütz-Meindl, 2016 ; Felhofer et al, 2021 ). Our results indicate, that Dyadobacter sp.…”

Broad Specific Xyloglucan:Xyloglucosyl Transferases Are Formidable Players in the Re-Modelling of Plant Cell Wall Structures

“…On the other hand, Raman spectroscopy and surface-enhanced Raman spectroscopic chemical imaging allowed investigating the mutual distribution and co-localisation of CW polysaccharides, such as pectin and XGs in, for example, onion cells [108]. Further, Felhofer and co-workers [109] described how CW thickening indentations were formed in primary CWs in algae at exactly defined areas, specifically where pectins and XGs co-localised, while in the secondary CWs, crystalline cellulose dominated in thickening areas. These observations allowed concluding that a denser network of cellulose micro-fibrils stiffened CWs at the indent and modified the CW extensibility.…”

Ultrastructure of plant cells

“…1, see also cover illustration of this issue). Felhofer et al (2021) nicely illustrate the cellular components and most interestingly differences in cellulose deposition in the young semi cells with a possible implication for cell shape formation. Again, this research was started by Ursula Lütz-Meindl in collaboration with Notburga Gierlinger from the University of Natural Resource and Life Sciences in Vienna, but fate did not allow the completion of this study during her lifetime.…”

“…As this issue emphasizes plant cells, several publications highlight the structure and function of cell walls and their adhesives (e.g. Holzinger et al 2021;Felhofer et al 2021;Domozych et al 2021;Medwed et al 2021). Moreover, Driouich al.…”