Cellular Calcium Distribution Modulates the Growth of Callus and Protoplasts of Halophyte Mangrove Plant, Avicennia Alba - an X-ray Microanalysis

Abstract

Two cultured cell lines were developed from cotyledons of a halophyte mangrove, Avicennia alba . In the high-Ca callus line , which was sub-cultured in a modified amino acid medium containing 3 mM CaCl 2 , growth of calluses and their protoplasts were both inhibited by low concentrations of CaCl 2 in the culture medium. Removal of Ca 2+ from the culture medium stimulated callus growth and the calluses could be sub-cultured without CaCl 2 (low-Ca callus line) . The intra- (cytoplasmic matrix and vacuole) and extra - (cell wall) cellular concentrations of elements, i.e., [ Ca], [K], [Cl], [Na], [Mg], [P] and [S] were investigated using quantitative X-ray microanalysis of cryosections of calluses from both cell lines . [Ca] was high in the cytoplasmic matrix and cell wall of the high-Ca line . [Ca] was lowered in the low-Ca line in all cell compartments , though still detected. Ca-containing electron-dense precipitates were accumulated in the middle lamella of cell walls in resin-embedded sections of the high-Ca line . CaCl 2 in the medium stimulated protoplast growth only in the low-Ca line . These results suggested that a low cellular [Ca] is needed for protoplasts growth of A. alba. The im portance of cellular [Ca] for the growth of halophilic mangrove plant cells was discussed.