title: Localization of calcium in roots and microsomal membranes of corn by direct pyroantimonate precipitation.
abstract: Many cell membrane systems, including microsomal vesicles of corn, are able to regulate calcium levels both in vivo and in vitro, often in an ATP-dependent, calmodulin-stimulated fashion. The purpose of this study was to determine calcium distribution in meristematic cells of intact tissue and microsomal vesicles from corn roots using direct pyroantimonate-osmium fixation. In root cells, precipitates were localized in mitochondria, plastids, the nucleus, endoplasmic reticulum, Golgi apparatus, and along the plasma membrane. Plasma membrane-enriched microsomal vesicles isolated from corn roots incubated in media to permit calcium transport before pyroantimonate-osmium fixation show internal precipitates associated with the membrane and in the lumen of the vesicles. De-staining of the sections with 1 mM EDTA or EGTA removed precipitate from the sections, confirming the presence of calcium in the antimonate precipitates. These data support biochemical data that this same membrane preparation exhibited ATP-dependent calcium sequestration that was stimulated by calmodulin, as measured by retention of 45Ca. This provides evidence that these membranes are responsible for ATP-requiring, calmodulin-stimulated calcium transport in the intact cell.
mesh_terms: D000965:Antimony; D002118:Calcium / Q000032:analysis*; D006651:Histocytochemistry; D008854:Microscopy, Electron / Q000379:methods; D009992:Osmium; D017892:Osmium Compounds; D010944:Plants / Q000378:metabolism*; D003313:Zea mays
chemical_list: D017892:Osmium Compounds; C012017:pyroantimonate-osmium; D009992:Osmium; D000965:Antimony; D002118:Calcium