Localization of Ca++-containing antimonate precipitates during mitosis

Area of Science:

• Plant cell biology
• Cellular and molecular biology
• Biochemistry

Background:

• Calcium ions (Ca++) play crucial roles in cellular processes, including cell division.
• Understanding the localization of intracellular calcium is vital for elucidating its regulatory functions.
• Previous studies have suggested calcium's involvement in mitosis and cytokinesis, but precise localization remains to be fully detailed.

Purpose of the Study:

• To localize intracellular bound calcium (Ca++) during mitosis and cytokinesis in plant cells.
• To investigate the association of calcium with specific organelles during cell division.
• To explore the potential role of calcium in regulating the mitotic apparatus.

Main Methods:

• In situ precipitation using potassium antimonate.
• Electron microscopy for visualization of antimonate deposits.
• Solubility tests (water, EDTA, EGTA) to identify the precipitated cation as Ca++.

Main Results:

• Antimonate deposits, indicating Ca++, were found in the endoplasmic reticulum (ER), vacuoles, euchromatin/nucleoplasm, and mitochondria in both Marsilea vestita and Hordeum vulgare.
• Mitochondria showed higher Ca++ density in Marsilea than in Hordeum.
• Smooth ER surrounding the mitotic spindle contained significant Ca++ deposits, suggesting a role in regulating the mitotic apparatus.

Conclusions:

• Intracellular calcium is localized in various organelles throughout mitosis and cytokinesis in the studied plant species.
• The endoplasmic reticulum (ER), especially the smooth ER associated with the mitotic spindle, is a significant site for calcium localization.
• The Ca++-binding capacity of the ER suggests its involvement in regulating free Ca++ levels critical for Ca++-sensitive processes during cell division.