Subcellular Localization of Calcium Ion within Cells of the Abscission Layer of Citrus Leaf Explants during Abscission

Abstract

Subcellular localization of calcium in the cells of the abscission layer and adjacent tissues was investigated electronmicroscopically by a Slocum and Roux's antimonate precipitation method using leaf explants of Calamondin (Citrus madurensis Lour.). Calcium localization, which was detected as electron-dense small particles, was determined by comparing the specimens which were fixed with fixatives with or without potassium antimonate. In fresh or IAA-treated explants only a few particles were present in the cells of the abscission layer along the plasmalemma and in the cytoplasm. In the explants which underwent some senescence, more particles were present along the plasmalemma and in the middle lamella of the cell wall, and a few in the cytoplasm and in the vacuole. In abscising explants, which were treated with trifluoperazine (TFP), abundant particles were present in the degenerated middle lamella. The role of calcium in senescence and abscission is discussed.