Ultrastructural Studies on the Ca²⁺ Localization in the Dividing Cells of the Maize Root Tip

Abstract

The distribution of Ca²⁺ in dividing cells of the maize root tip was examined by potassium pyroantimonate precipitation and EGTA treatment methods. Ca²⁺ was found in most of the cell organelles, such as the matrix of the mitochondria, the thylakoid membrane of the proplastid and the Golgi vesicles, and on the plasma membrane. Ca²⁺ was also distributed throughout the cytoplasmic ground matrix and attractoplasm, inside the vacuoles, in the granular zone of the nucleolus in the interphasic nucleus and in the regenerated nucleolus in the telophasic nucleus. The amounts of Ca²⁺ distributed in the cytoplasmic ground matrix, the vacuole and the nucleolus varied during nuclear division. From the results of the present experiment, the following considerations on the role of Ca²⁺ and the regulation site of Ca²⁺ in dividing plant cells were drawn: 1) Ca²⁺ may play a role in the construction of the granular form of the ribosome. 2) Ca²⁺ may be an essential ion in the regeneration of nucleolus. 3) Vacuoles may act as the regulatory site of the Ca²⁺ concentration in the cytoplasm and attractoplasm in plant cells. Spindle microtubules and phragmo-microtubules are probably surrounded by other ions, such as Mg²⁺.