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Osmotic Homeostasis in Dictyostelium Discoideum : Excretion of Amino Acids and Ingested Solutes
Author(s) -
STECK THEODORE L.,
CHIARAVIGLIO LUCIUS,
MEREDITH STEPHEN
Publication year - 1997
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.1997.tb05731.x
Subject(s) - dictyostelium discoideum , amino acid , biology , biochemistry , contractile vacuole , glycine , vacuole , osmotic shock , endocytic cycle , cytosol , cytoplasm , excretion , osmoregulation , microbiology and biotechnology , endocytosis , enzyme , cell , ecology , salinity , gene
. The response to osmotic stress in axenically cultured Dictyostelium discoideum was examined. Hypoosmotic buffers elicited two changes in the large (‐50 mM) cytosolic pool of amino acids: a) the total size of the pool diminished, while b) about half of the initial pool was excreted. Hyperosmotic stress had the opposite effect. Among the predominant amino acids in the pool were glycine, alanine and proline. Putrescine, the major diamine, was neither excreted nor modulated. Recently ingested radioactive amino acids were excreded in preference to those in the cytoplasm, suggesting that the endocytic pathway might be involved in water excretion. Furthermore, hypoosmotic stresss strimulated the selective exretion of small, membrane‐impermeable fluorescent dyes which had been ingested into endocytic vacuoles. Caffeine inhibited the excretion of the fluorophores but not the amino acids. We conclude that the response of Dictyostelium to osmotic stress is complex and includes both modulation of the cytoplasmic amino acid pool and the excretion of amino acids and other small solutes from the endocytic pathway.