title: Regulation of anaphase chromosome motion in Tradescantia stamen hair cells by calcium and related signaling agents.
abstract: Several lines of evidence support the idea that increases in the intracellular free calcium concentration [( Ca2+]i) regulate chromosome motion. To directly test this we have iontophoretically injected Ca2+ or related signaling agents into Tradescantia stamen hair cells during anaphase and measured their effect on chromosome motion and on the Ca2+ levels. Ca2+ at (+)1 nA for 10 s (approximately 1 microM) causes a transient (20 s) twofold increase in the rate of chromosome motion, while at higher levels it slows or completely stops motion. Ca2+ buffers, EGTA, and 5,5'-dibromo-1,2- bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, which transiently suppress the ion level, also momentarily stop motion. Injection of K+, Cl-, or Mg2+, as controls, have no effect on motion. The injection of GTP gamma S, and to a lesser extent GTP, enhances motion similarly to a low level of Ca2+. However, inositol 1,4,5-trisphosphate, ATP gamma S, ATP, and GDP beta S have no effect. Measurement of the [Ca2+]i with indo-1 reveals that the direct injections of Ca2+ produce the expected increases. GTP gamma S, on the other hand, causes only a small [Ca2+]i rise, which by itself is insufficient to increase the rate of chromosome motion. Further studies reveal that any negative ion injection, presumably through hyperpolarization of the membrane potential, generates a similar small pulse of Ca2+, yet these agents have no effect on motion. Two major conclusions from these studies are as follows. (a) Increased [Ca2+]i can enhance the rate of motion, if administered in a narrow physiological window around 1 microM; concentrations above 1 microM or below the physiological resting level will slow or stop chromosomes. (b) GTP gamma S enhances motion by a mechanism that does not cause a sustained uniform rise of [Ca2+]i in the spindle; this effect may be mediated through very localized [Ca2+]i changes or Ca2(+)-independent effectors.
authors.affiliation: Department of Botany, University of Massachusetts, Amherst 01003.
authors.forename: D H
authors.initials: DH
authors.lastname: Zhang
authors.forename: D A
authors.initials: DA
authors.lastname: Callaham
authors.forename: P K
authors.initials: PK
authors.lastname: Hepler
mesh_terms: D000227:Adenine Nucleotides / Q000494:pharmacology; D000705:Anaphase; D002118:Calcium / Q000502:physiology*; D002875:Chromosomes / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D004533:Egtazic Acid / Q000494:pharmacology / Q000031:analogs & derivatives; D006150:Guanine Nucleotides / Q000494:pharmacology; D007700:Kinetics; D008856:Microscopy, Fluorescence / Q000295:instrumentation / Q000379:methods; D059828:Plant Cells; D018521:Plant Physiological Phenomena; D010944:Plants / Q000648:ultrastructure
chemical_list: D000227:Adenine Nucleotides; D006150:Guanine Nucleotides; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium