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  • 1
    ISSN: 1615-6102
    Keywords: Dictyostelium mucoroides ; Cellular slime mold ; Cytoplasmic pH ; Ethylene ; Cyclic AMP ; Sexual development ; Macrocyst ; Sorocarp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Dictyostelium mucoroides-7 (Dm 7) and a mutant MF 1 derived from it exhibit two developmental pathways: sorocarp formation occurs during the asexual process, and macrocyst formation during the sexual cycle. The two developmental pathways are mainly regulated by two chemical substances: 3′,5′-cyclic adenosine monophosphate (cAMP) and ethylene. Recently, we have demonstrated that cytoplasmic pH (pHi) has a critical role for the choice of developmental pathways, higher pHi being favourable to macrocyst formation. Thereupon, attention was riveted to the relation of pHi to biosynthesis of cAMP and ethylene. Effect of pHi on the production and release of ethylene, a potent inducer of macrocyst formation, was examined, using the two facing culture method. The result showed that lowered pHi inhibits ethylene production, thus resulting in a failure of cells to form macrocysts. The accumulation of cAMP, an inhibitor of macrocyst formation, was found to vary depending on extracellular pH (pHo), but diethylstilbestrol (DES) that is a proton pump inhibitor and also an inhibitor of macrocyst formation had no significant effect on the accumulation. Taken together these results indicate that higher pHi may induce macrocyst formation through enhancement of ethylene production rather than inhibition of cAMP synthesis.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 167 (1992), S. 159-168 
    ISSN: 1615-6102
    Keywords: Dictyostelium mucoroides ; Ethylene ; Sexual development ; Macrocyst ; Sorocarp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cellular slime moldDictyostelium mucoroides-7 (Dm 7) and its mutant (MF 1) exhibit sexual or asexual development depending upon culture conditions. During the sexual cycle macrocyst formation occurs, whereas sorocarps containing spores and stalk cells are asexually formed. As previously reported, the macrocyst formation is marked by the emergence of true zygotes, and is induced by a potent plant hormone, ethylene. The concentration of ethylene required for macrocyst induction was determined to establish the similarity of ethylene action between this organism and higher plants. Macrocysts are induced by low (1 μl/l) exogenous concentrations of ethylene. Higher concentrations (10–1,000 ul/l) also gave essentially the same inductive activity. Ethionine, an analogue of methionine, was found to inhibit zygote formation during sexual development through its interference with ethylene production by Dm 7 and MF 1 cells. In fact, the inhibitory effect of ethionine was mostly nullified by the application of ethylene, S-adenosyl-L-methionine, or 1-aminocyclopropane-1-carboxylic acid. Taken together these results suggest that both the effective concentration of ethylene and the pathway of ethylene biosynthesis inD. mucoroides may be similar to those in higher plants. Ethylene was also found to be produced in various species and strains of cellular slime molds, even during the asexual process. The possible functions of ethylene in the asexual development are discussed in relation to cell aggregation and differentiation.
    Type of Medium: Electronic Resource
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