Subcellular localization of Ca2+ in the stigmatic surface of developing olive pistils. (A) Stigmatic surface of the pistil enclosed in a green flower bud (stage 1). No electron-dense precipitates can be found in the stigma surface or in the papillae cells. (B) Stigmatic papillae at the beginning of flower opening (stage 2): a few Ca/Sb precipitates are localized on the outer surface of the papilla cell walls (arrowheads). (C) Stigmatic papillae of a completely open flower with turgid anthers (stage 3): thick layer of exudate that has plentiful electron-dense precipitates is present on the outer stigmatic surface. (D) Magnified area of a rich exudate layer (inset, area marked with the dashed line) present on the stigmatic surface at the time of anther dehiscence (stage 4). Numerous, small Ca/Sb precipitates are located exclusively over the electron-dense matrix of the exudates (arrowheads). (E) In the stigma of a flower without petals and anthers (stage 5), Ca/Sb deposits are less abundant and present mainly on the surface of degenerating papillae cells and pollen grains (arrowheads); PG - pollen grain, PP - papillae cell, EX - exudate. Bar = 1 μm.