ISSN:
1615-6102
Keywords:
Cell cycle
;
Microtubule
;
Macrotubule
;
Mitosis
;
Physarum
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary Mitotically synchronous plasmodia of the slime moldPhysarum polycephalum were subjected to brief exposures of either pure atmospheres of carbon dioxide or nitrogen gases or to pulsetreatments with respiratory poisons (sodium azide, sodium arsenate, or 2,4-dinitrophenol, DNP) at many different phases of the mitotic cycle to assess their effects on the mechanism(s) controlling the timing of mitosis. Plasmodia were fully viable after a pulse of CO2 lasting up to 90 minutes or after a N2-pulse of 30 minutes in duration. Upon return to normal aeration, all treated plasmodia entered a fully synchronous mitosis with a variable excess mitotic delay, which was dependent on the duration of the pulse and time of application in the mitotic cycle. Likewise, plasmodia exposed to 15-minute-pulses of a sublethal dose of sodium arsenate (0.1 mM), sodium azide 0.05 mM) and 2,4-DNP (0.2 mM) yield characteristic patterns of excess mitotic delay upon returnal to normal culture conditions. Two different types of phase response curves (PRC) were generated by these treatments. This suggests that at least two distinct respiratory-linked physiological mechanisms are involved in control of mitosis onset and regulation of mitotic timing inPhysarum. Electron microscope observations of CO2-treated plasmodia reveal the induction of intranuclear 40–60 nm diameter macrotubules at all stages of the G2 phase up to and including prometaphase. Both anoxia and sodium azide treatments are effective in macrotubule induction, and both reversibly disrupt the normal tubular cristae organization of mitochondria. In early G2, macrotubules polymerize in association with both the inner membrane of the nuclear envelope and the nucleolus, while the tubule-organizer region, TOR, serves as the only nucleating site for macrotubules in late G2 nuclei, coincident with the onset of mitosis and TOR formation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01279223
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