NCBI Taxonomy ID 131210


Apical Vacuoles

Found at both ends. Barium sulfate crystals in constant movement. Long thought to be calcium sulfate. Movement not brownian. Barium sulfate is insoluble in water. Perhaps used as statolith (gravity sensor).

This guy likes to move around:


The Biology of Desmids, A.J.Brook 1981.

Selectivity in biomineralization of barium and strontium.

Krejci MR, Wasserman B, Finney L, McNulty I, Legnini D, Vogt S, Joester D.

Department of Materials Science and Engineering, Northwestern University, 2220
Campus Drive, Evanston, IL 60208, USA; X-ray Science Division, Argonne National
Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA.

The desmid green alga Closterium moniliferum belongs to a small number of
organisms that form barite (BaSO(4)) or celestite (SrSO(4)) biominerals. The
ability to sequester Sr in the presence of an excess of Ca is of considerable
interest for the remediation of (90)Sr from the environment and nuclear waste.
While most cells dynamically regulate the concentration of the second messenger
Ca(2+) in the cytosol and various organelles, transport proteins rarely
discriminate strongly between Ca, Sr, and Ba. Herein, we investigate how these
ions are trafficked in C. moniliferum and how precipitation of (Ba,Sr)SO(4)
crystals occurs in the terminal vacuoles. Towards this goal, we simultaneously
visualize intracellular dynamics of multiple elements using X-ray fluorescence
microscopy (XFM) of cryo-fixed/freeze-dried samples. We correlate the resulting
elemental maps with ultrastructural information gleaned from freeze-fracture
cryo-SEM of frozen-hydrated cells and use micro X-ray absorption near edge
structure (micro-XANES) to determine sulfur speciation. We find that the kinetics
of Sr uptake and efflux depend on external Ca concentrations, and Sr, Ba, and Ca 
show similar intracellular localization. A highly ion-selective cross-membrane
transport step is not evident. Based on elevated levels of sulfate detected in
the terminal vacuoles, we propose a "sulfate trap" model, where the presence of
dissolved barium leads to preferential precipitation of (Ba,Sr)SO(4) due to its
low solubility relative to SrSO(4) and CaSO(4). Engineering the sulfate
concentration in the vacuole may thus be the most direct way to increase the Sr
sequestered per cell, an important consideration in using desmids for
phytoremediation of (90)Sr.



... RuBisCo ...
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