title: Plasma membrane domains participate in pH banding of Chara internodal cells.
abstract: We investigated the identity and distribution of cortical domains, stained by the endocytic marker FM 1-43, in branchlet internodal cells of the characean green algae Chara corallina and Chara braunii. Co-labeling with NBD C(6)-sphingomyelin, a plasma membrane dye, which is not internalized, confirmed their location in the plasma membrane, and co-labelling with the fluorescent pH indicator Lysotracker red indicated an acidic environment. The plasma membrane domains co-localized with the distribution of an antibody against a proton-translocating ATPase, and electron microscopic data confirmed their identity with elaborate plasma membrane invaginations known as charasomes. The average size and the distribution pattern of charasomes correlated with the pH banding pattern of the cell. Charasomes were larger and more frequent at the acidic regions than at the alkaline bands, indicating that they are involved in outward-directed proton transport. Inhibition of photosynthesis by DCMU prevented charasome formation, and incubation in pH buffers resulted in smaller, homogenously distributed charasomes irrespective of whether the pH was clamped at 5.5 or 8.5. These data indicate that the differential size and distribution of charasomes is not due to differences in external pH but reflects active, photosynthesis-dependent pH banding. The fact that pH banding recovered within several minutes in unbuffered medium, however, confirms that pH banding is also possible in cells with evenly distributed charasomes or without charasomes. Cortical mitochondria were also larger and more abundant at the acid bands, and their intimate association with charasomes and chloroplasts suggests an involvement in carbon uptake and photorespiration.
authors.affiliation: Department of Cell Biology, Division of Plant Physiology, University of Salzburg, 5020 Austria.
authors.forename: Patric M
authors.initials: PM
authors.lastname: Schmölzer
authors.forename: Margit
authors.initials: M
authors.lastname: Höftberger
authors.forename: Ilse
authors.initials: I
authors.lastname: Foissner
mesh_terms: D002021:Buffers; D044784:Chara / Q000166:cytology* / Q000378:metabolism* / Q000648:ultrastructure; D004237:Diuron / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D010788:Photosynthesis / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D017494:Proton Pumps / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism
chemical_list: D002021:Buffers; C073804:FM1 43; D017494:Proton Pumps; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D004237:Diuron; D006180:Proton-Translocating ATPases