Localization Of Calcium In Cells Research Articles

Sub‐cellular Localization of Calcium in Azolla‐Anabaena Symbiosis by Chlortetracycline, ESI and EELS

AbstractThe subcellular localization of calcium in cells of symbiotic partners located within leaf cavities of Azolla was investigated by using chlorotetracycline, ESI and EELS analysis. Loosely membrane‐bound calcium was evidenced by using CTC or EGTA and CTC, in cytoplasmic regions of Azolla hair cells and in cytoplasm of the cyanobiont. Tightly membrane‐bound calcium revealed by CTC, and ESI and EELS analysis, was observed in cyanophycin granules and carboxysomes of the cyanobiont. A third calcium type, revealed by ESI and EELS analysis, was localized at the level of cell walls of simple and branched Azolla hairs, in the envelope of heterocysts, and in the cell walls of the cyanobiont.

Ultrastructural localization of calcium in the chick chorioallantoic membrane as revealed by cytochemistry and X-ray microanalysis.

The chorioallantoic membrane (CAM) of the chick embryo actively transports calcium from the egg shell into the embryonic circulation. To investigate the intracellular pathway of calcium transport across the CAM, ultrastructural localization of intracellular calcium in cells of the chorionic ectoderm (CE) was determined using cytochemical methods and X-ray microanalysis. Treatment of the CE with potassium oxalate, potassium ferricyanide or potassium pyroantimonate revealed large numbers of electron-dense granules (EDGs) in the ectodermal cells. These measure 30-40 nm in diameter, and are not membrane-bound. These granules were seen in all three cell types of the CE. The presence of calcium in the EDG was directly confirmed by X-ray microanalysis. When strontium or barium ions were applied to the shell membrane side of the CAM, the cells of the CE incorporated these divalent cations and sequestered them in granules (25-40 nm in diameter) in cytoplasm and mitochondria. This study indicates that calcium enters the CE cells by means other than endocytosis, as the EDGs are not membrane-bound, that all three types of the CE cells appear to function in transport of calcium from shell to embryo during embryogenesis, and that the EDG plays important roles in intracellular accumulation of calcium during the process of calcium transport across the chorioallantoic membrane.

HOW ROOTS PERCEIVE AND RESPOND TO GRAVITY

Graviperception by plant roots is believed to occur via the sedimentation of amyloplasts in columella cells of the root cap. This physical stimulus results in an accumulation of calcium on the lower side of the cap, which in turn induces gravicurvature. In this paper we present a model for root gravitropism integrating gravity-induced changes in electrical potential, cytochemical localization of calcium in cells of gravistimulated roots, and the interdependence of calcium and auxin movement. Key features of the model are that 1) gravity-induced redistribution of calcium is an early event in the transduction mechanism, and 2) apoplastic movement of calcium through the root-cap mucilage may be an important component of the pathway for calcium movement.