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1.
F. CROUTE D. DUPOUY J. P. CHARLEY J. P. SOLEILHAVOUP H. PLANEL 《The Journal of eukaryotic microbiology》1980,27(1):132-135
SYNOPSIS Catalase activity of Paramecium tetraurelia decreased during autogamy and recovered to normal 5 days later. Autogamy also caused changes in the ciliate's sensitivity to natural ionizing radiations—the decrease in cell growth rate previously described in shielded cultures did not occur when autogamous cells were used. Maximum effect of shielding was observed in 11-day-old postautogamous cells. the role of the catalase in the mechanism of natural irradiation effect is discussed. 相似文献
2.
SYNOPSIS. The effect of temperature on the behavior of swimming cells of Paramecium caudatum has been investigated by photographic analyses of their tracks in uniform temperature, in temperature gradient, or in temperature changing with time. When the cells were placed in the temperature gradient, the frequency of discontinuous directional changes of cells swimming toward the optimal temperature, the temperature of the culture, was much lower than that of the cells swimming in the opposite direction. This difference in the frequency of directional changes explained the observed accumulation of the cells at - the optimal temperature. When the temperature was suddenly changed toward the optimum, a transient decrease of the frequency of directional changes was observed and when the temperature was changed in the reverse direction, a transient increase of the frequency was noted. This transient response to the temperature change was the origin of the dependence of the frequency of directional changes on the swimming direction in the temperature gradient. Finally, the relation between the magnitude of the transient response and the rate of the temperature change was derived. 相似文献
3.
Codon Usage in Tetrahymena and Other Ciliates 总被引:6,自引:0,他引:6
DUANE W. MARTINDALE 《The Journal of eukaryotic microbiology》1989,36(1):29-34
Codon usage in ciliates was examined by analyzing the coding regions of 22 ciliate genes corresponding to a total of 26, 142 nucleotides (8, 714 codons). It was found that Tetrahymena, Paramecium and the hypotrichs ( Oxytricha and Stylonychia ) differed in which synonymous codons were used most frequently by their genes. In fact, the codon choices in highly expressed Tetrahymena genes were more similar to those of yeast genes than those of Paramecium genes. The ciliates do not appear to have unusually strong biases in codon usage frequency when compared to other protists such as yeast. The analysis of the Tetrahymena genes indicated that genes which are highly expressed during normal cell growth have a stronger bias towards using the "preferred" codons than those expressed at lower levels during growth or for brief periods during processes such as conjugation. This conforms to what is found in other protists. 相似文献
4.
K. Oami 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1996,178(3):307-316
Membrane potential responses of a ciliate protozoan Paramecium caudatum to the external application of quinine were investigated in relation to its motile activities. Wild-type specimens swimming in the reference solution did not enter into a quinine-containing (0.5 mM) test solution due to avoiding responses exhibited at the border between the two solutions, and therefore stayed in the reference solution (chemodispersal). Squirting of a quinine-containing test solution over a wild-type specimen evoked a train of action potentials superimposed on a depolarizing chemoreceptor potential. Squirting of a quinine-containing test solution over a CNR-mutant specimen defective in voltage-gated Ca2+ channel evoked only chemoreceptor potentials, which consisted of an initial transient depolarization, a following transient hyperpolarization and a sustained depolarization. A current-evoked action potential became larger in its amplitude and longer in its duration with the external application of quinine. Under the voltage-clamp condition, the fast inward current did not change whereas the delayed outward current decreased with the external application of quinine. It is concluded that quinine is a potent repellent for Paramecium because it produces a depolarizing chemoreceptor potential which evokes action potentials and prolongs the duration of the action potential. 相似文献
5.
Paramecium tetraurelia wild-type (7S) cells respond to 2.5 mm veratridine by immediate trichocyst exocytosis, provided [Ca2+]
o
(extracellular Ca2+ concentration) is between about 10–4 to 10–3
m as in the culture medium. Exocytosis was analyzed by light scattering, light and electron microscopy following quenched-flow/ freeze-fracture analysis. Defined time-dependent stages occurred, i.e., from focal (10 nm) membrane fusion to resealing, all within 1 sec.Veratridine triggers exocytosis also with deciliated 7S cells and with pawn mutants (without functional ciliary Ca channels). Both chelation of Ca2+
o
or increasing [Ca2+]
o
to 10–2
m inhibit exocytotic membrane fusion. Veratridine does not release Ca2+ from isolated storage compartments and it is inefficient when microinjected. Substitution of Na+
o
for N-methylglucamine does not inhibit the trigger effect of veratridine which also cannot be mimicked by aconitine or batrachotoxin. We conclude that, in Paramecium cells, veratridine activates Ca channels (sensitive to high [Ca2+]
o
) in the somatic, i.e., nonciliary cell membrane and that a Ca2+ influx triggers exocytotic membrane fusion. The type of Ca channels involved remains to be established.We thank Dr. C. Kung (Madison, WI) for providing the pawn mutant, Drs. G. Lehle and R. Waldschütz-Schüppel (Konstanz, Germany) for their help with light scattering experiments, and Ms. E. Dassler and D. Bliestle for continuous help during the extensive photographic documentation. This work has been supported by Deutsche Forschungsgemeinschaft, Schwerpunkt Neue mikroskopische Techniken für Biologie und Medizin (grant P178/11) and SFB156/B4. 相似文献
6.
7.
Regio- and stereo-specific nitrile hydrolysis by the nitrile hydratase from Rhodococcus AJ270 总被引:1,自引:0,他引:1
Alan J.Blakey JohnColby EdwinWilliams CatherineO'Reilly 《FEMS microbiology letters》1995,129(1):57-61
Abstract Acid phosphatase activity was measured in individual cells by determining their optical densities through a scanning confocal laser microscope. The naphthol AS-TR (3-hydroxy-2-naphtoic acid 4'-chloro-2'-methylanilide) phosphate-hexazotized para-rosanilin method was used to visualise the acid phosphatase content in the light microscope. Evidence was obtained that the amount of enzyme varied in exponential growth phase cells as the fission age increased. By comparing the acid phosphatase activity with the rate of food vacuole formation, it appeared that the amount of enzyme inside the cells decreased in early clonal life, whereas the rate of food uptake increased. It was assumed that the reduction of acid phosphatase content could lead to a more extended life of vacuoles and to a decreased membrane recycling rate. In turn, the reduced supply of membrane available for food vacuole formation could partly be responsible for the decrease of the food uptake rate observed after the initial increase. 相似文献
8.
Mating type determination in Tetrahymena thermophila involves developmentally programmed, heritable alterations of the macronucleus, localized to the mtd locus. This determination can be predictably controlled by the environmental conditions during macronuclear development, eg, temperature and time of refeeding. In this article we have further characterized the effects of delayed refeeding on mating type determination, as revealed by the frequency of mating types among the progeny of a cross. Our results show that 1) the magnitude of this starvation effect decreases with temperature of conjugation and becomes undetectable at 18°C; 2) starvation during the interval 14 to 22 hr (after conjugation is induced at 30°C) is a necessary and sufficient condition for the induction of starvation effects; 3) relative mating type frequencies vary monotonically with nutrient concentration present during this critical period; and 4) sister macronuclei, developing under starvation conditions in the same cytoplasm, differentiate majority mating types characteristic of early or late refeeding; sister macronuclei show no apparent correlation with each other. On the basis of our observations on early and late refed cells, we propose that the composition of the newly developed macronucleus is the outcome of two key events: 1) mating type determination at the mtd locus and 2) differential molecular cloning of generally one or two autonomously replicating fragments (ARFs) of the macronuclear DNA bearing the mtd locus. 相似文献
9.
SYNOPSIS Triplet conjugants of Paramecium caudatum which appeared naturally in mating mixtures and those of Paramecium multimicronucleatum which were produced by conjugation-inducing chemicals were isolated. Triplet conjugants lasting for more than 3 h were stained to examine macronuclear events. In P. caudatum , only 2 triplets among 182 (1%) contained macronuclear fragmentation in all 3 members. The most frequently occurring triplets (79%) were those producing 1 cell without and 2 cells with macronuclear fragments. There were also triplets (17%) producing 1 cell with, and 2 without macronuclear fragments, and some (3%) with 3 cells that contained no fragments. The length of persistence of the triplet was not responsible for the occurrence of macronuclear fragmentation in the 3rd cell of the triplet. In P. multimicronucleatum , the same 4 classes of triplets occurred, but the most frequently occurring class was that consisting of 3 cells (91%) with macronuclear fragments. Induction of nearly 100% of triplets with 3 such cells was possible by isolating the triplets' from a culture which was treated chemically at about 24 h after the last feeding. Treatment with chemicals in starved cultures resulted in triplets with incompletely fragmented or nonfragmented macronuclei. Further, in P. multimicronucleatum , chemicallyinduced triplets involving only holdfast pairs to which the 3rd cells were uniting often produced 3 cells with fragmented macronuclei. 相似文献
10.
SYNOPSIS In a culture system of Paramecium bursaria , virus particles were found in large number. The particle was able to infect and multiply in certain cells of the zoochlorella, an intracellular symbiotic alga of P. bursaria. The infective particle, designated as zoochlorella cell virus (ZCV), was icosahedral and 120–180 nm in edge to edge diameter. The ZCV particle was found to differ from any of the already established viruses attacking the green and the blue-green algae. Within the system where P. bursaria cells were growing, ZCV particles were detected in the depression of the pellicle, among the cilia growing in the cytopharynx, and in the food vacuole of P. bursaria. ZCV particles were infective only for the zoochlorella cells which were recently released from the cytoplasm of P. bursaria. The multiplication process of ZCV comprised the adsorption of the particle to the cell wall of the zoochlorella, the penetration of nucleic acid into the host cell interior, the replication of viral constituents, the maturation of viral particles and their final release by the burst of the zoochlorella cell. ZCV particles appeared only in the cytoplasmic region of the zoochlorella cell in which many ribosomes were distributed. A possible ecosystem among the 3 members consisting of P. bursaria , zoochlorella and ZCV is discussed. 相似文献