Role of calcium in abscission of citrus

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To study the role of calcium in abscission of citrus, 1) interaction of brassinolide (BR) and trifluoperazine (TFP), an. initiator of calamondin- calcium complex in abscission, 2) subcellular localization of calcium during senescence and abscission of leaf explants, were investigated. BR, a novel plant growth-regulating steroidal lactone, markedly retarded the abscission of leaf explants of Calamondin (Citrus maduretisis Lour.), when dissolved in itiator and fed through the petiole. BR was effective at concentrations as low as 0.021muM, and showed a stronger effect than IAA which also retarded abscission. TFP, an inhibitor of the calmodulin-calcium complex, accelerated abscission, and this acceleration could be counteracted by a simultaneous addition of IAA or BR, the effect of IAA being stronger. This suggests the mechanism of retardation of abscission by BR may be different from that of IAA. BR and IAA also markedly retarded and TFP accelerated the abscission of fruitlet explants of … More Calamondin.Subcellular localization of calcium in the cells of abscission layer and adjacent parencliyma tissue was investigated electronmicroscopically by Slocum and. Roux's antimonate precipitation method using leaf explants of Calamondin. By comparing the specimens which were fixed with fixatives with or without potassium antimonate, calcium was detected as electron-dense small particles and that was thought to be free calcium ion. In fresh or IAA-treated explants only a few particles were present in the cells of abscission layer maiixly along plasmalemma. In the explants which uiiderwetit some senescence, more particies were present in these cells along pasmalemma but also in, cytoplasm and middle lamella of tile cell wall. In abscising explants which were treated with trifluoperazine(TFP), abundant particles were present in the degenerated middle lamella. These results show that the amount, type and subcellular localization of calcium present in the cells of abscission layer closely related to the abscission. Less