Localization of Ca++-containing antimonate precipitates during mitosis.

Abstract

Intracellular bound Ca" has been localized throughout mitosis and cytokinesis in two plant species by means of in situ precipitation with potassium antimonate and electron microscope visualization . Identification of Ca" as the major cation precipitated was made by comparing solubility properties in water, EDTA, and ECTA of the intracellular deposits with respect to those of K +-, Mg"-, and Ca"-antimonate standards. In spermatogenous cells of the water fern, Marsilea vestita, and stomatal complex cells of barley, Hordeum vulgare, antimonate deposits have been found associated with the endoplasmic reticulum (ER), vacuoles, euchromatin/nucleoplasm, and mitochondria . The last contain a much higher density of precipitates in Marsilea than in Hordeum . Dictyosomes and the nuclear envelope of Marsilea also contain antimonate deposits, as do the plasmalemma, cell wall, and phragmoplast vesicles of Hordeum . Microtubule-organizing centers such as kinetochores and the blepharoplast of Marsilea do not stain . In spite of differences in associated antimonate between certain organelles of the two species, the presence of antimonate along the ER throughout the cell cycle is common to both .Of particular interest are those precipitates seen along the tubules and cisternae of the extensive smooth ER that surrounds and invades the mitotic spindle in both species. The ability to bind divalent cations makes the mitotic apparatus (MA)-associated ER a likely candidate for regulation of free Ca" levels in the immediate vicinity of structural components and processes that are Ca'-sensitive and proposed to be Ca"-regulated.

Calcium: A Central Regulator of Plant Growth and Development

“…This general idea, which Barry Palevitz and I articulated in our review on the cytoskeleton (Hepler and Palevitz, 1974), guided research in my laboratory for several years thereafter. Spindle-associated endoplasmic reticulum was found to contain deposits of Ca 21 (Wick and Hepler, 1980;Wolniak et al, 1983), and spindle microtubules were shown to be sensitive to elevations in [Ca 21 ] i with depolymerization occurring when the concentration was raised to 1.0 mM or more (Zhang et al, 1992). Restriction of the [Ca 21 ] i was seen to affect progress through mitosis (Hepler, 1985), whereas stimulation of Ca 21 entry was found to promote bud initial formation in mosses (Saunders and Hepler, 1982) and red light-stimulated spore development in ferns (Wayne and Hepler, 1984).…”

Pollen tube tip growth

“…It is possible that the use of calcium-stabilizing buffers (e.g. Wick & Hepler, 1980;Watt et al, 1987) would have retained more calcium in the tube. Addition of CTC to the growth meclia prior to harvesting tor the analysis does lead to an increased level of calcium at the tube tips (Reiss et al, 1983).…”

Tansley Review No. 21 Plant ion channels: whole‐cell and single channel studies

“…Whole-cell free Ca^^ may rise during anaphase (Hepler & Callahan, 1987), which might be related to plasma membrane Ca"'ĉ hannel activity. The possibility of the control of mitotic spindle activity by localized Ca'^^ channels in the endoplasmic reticulum (ER) should also be considered further (Wick & Hepler, 1980). Measurements of current around developing plant tissues (Jaffe & Nuccitelli, 1977) may be niediated in part by ion channels, but active pumping of ions also appears to be involved (Schreurs & Harold, 1988).…”