Cubic plasma membrane domains stabilize and restrict zones for pH band formation in Chara internodal cells

ABSTRACT

Characean internodal cells display acid and alkaline regions along their surface when exposed to light. The acidification facilitates uptake of carbon required for photosynthesis. In the genus Chara, cubic plasma membrane domains, known as charasomes, were first described five decades ago. Their size and abundance varies along the cell surface and it has been conjectured that the charasome coverage correlates with the pH banding pattern. In this study, we used fluorescein isothiocyanate-dextran (FITC-dextran) and confocal laser scanning microscopy to map the pH profile at high spatial and temporal resolution. In parallel, we stained the charasomes with styryl dyes and investigated their distribution in relation to the fluorescence pattern of FITC-dextran. In both internodal cells of the branchlets and of the main axis, we found that charasomes were small and sparse at the alkaline bands but large and abundant at the acidic regions. Our findings confirm the existence of cell surface regions predisposed to generate either high or low pH zones. We provide evidence that areas with high charasome abundance stabilize and restrict the position of the acidic bands whereas regions with low charasome abundance allow the formation of either stable or unstable alkaline bands.

KEYWORDS:

• Charasomes
• FITC-dextran
• green alga
• pH banding
• plant
• plasma membrane domains

Acknowledgments

The authors would like to thank Prof. Mary Beilby (USW, Sydney, Australia) and Prof. Alexander Bulychev (Lomonosov University, Moscow, Russia) for critically reading the manuscript and Dr Christian Pritz (Hebrew University of Jerusalem, Israel) for help in obtaining false colour images by ratio imaging.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This research was funded by the Austrian Science Fund (FWF) project P27536-B16.

Notes on contributors

Marketa Absolonova

Marketa Absolonova has recently earned her PhD in biology at the University of Salzburg and works in the group of Prof. Ilse Foissner. She did research on plasma membrane domains and pH banding pattern in Chara australis. Contribution: performing the confocal laser scanning microscopy on Chara branchlet internodal cells, analysing the respective data, designing Figures 1–3, Figure 6 and Supplementary Figure 1 and discussion of the results.

Ilse Foissner

Ilse Foissner is a biologist and Associate Professor at the University of Salzburg. She has written over 50 articles and she is teaching plant cell biology and cell imaging methods. Her research focuses on the biology of characean green algae, and her interests encompass wound healing, cytoskeleton, endocytosis, pH banding, charasome formation and degradation. Contribution: creating the research project P27536-B16 “Plasma membrane domains in internodal cells of the characean green algae: photosynthesis, ion currents, membrane potential and proteomics” funded by the Austrian Science Fund (FWF), designing the research and writing the article.

Aniela Sommer

Aniela Sommer has a background in physical sciences and is Senior Research Technician at the University of Salzburg in the Group of Prof. Ilse Foissner. She specializes in live cell imaging and digital image processing. Contribution: performing the confocal laser scanning microscopy on Chara internodal cells of the main axis, analysing the data, creating Figures 4 and 5 and Supplementary Figure 2, and discussion of the results.