A new type of plasmodium formation inPhysarum polycephalum

SUMMARYHaploid amoebae ofPhysarum polycephalummay form plasmodia sexually by ‘crossing’, which involves cellular and nuclear fusion, or asexually by ‘selfing’, which occurs without nuclear fusion. In most amoebal strains, selfing is seen in clonal cultures only at very low frequency. In the present study, we have shown that selfing occurs at a similarly low frequency in mixtures of crossing-incompatible amoebae, but is stimulated in crossing-compatible mixtures. In certain compatible mixtures involving mutant strains, where crossing is temperature-sensitive, selfing may be stimulated even at a temperature that largely or wholly abolishes crossing. The extent to which selfing is stimulated appears to be influenced bymatB, a locus which is known to affect the frequency of amoebal fusion. We have failed to detect any filter-transmissible factor that might be responsible for the effects we have observed. We suggest a sequence of events that might bring about ‘stimulated selfing’ as a consequence of abortive crossing.

Download Full-text

A review of unusual VLF bursty-patches observed in Northern Finland for Earth, Planets and Space

Earth Planets and Space ◽

10.1186/s40623-021-01516-y ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Claudia Martinez-Calderon ◽

Jyrki K. Manninen ◽

Jemina T. Manninen ◽

Tauno Turunen

Keyword(s):

Low Frequency ◽

Spectral Features ◽

Radio Waves ◽

Very Low Frequency ◽

Ground Station ◽

New Type ◽

The Moment ◽

Electron Gyrofrequency ◽

Different Characteristics ◽

Large Frequency

AbstractUsing numerical filtering techniques allowing us to reduce noise from sferics, we are able to clearly study a new type of differently structured very low frequency (VLF) radio waves above f = 4 kHz at the ground station of Kannuslehto in northern Finland (KAN, MLAT = 64.4°N, L = 5.5). These emissions are intriguing, since they are detected at frequencies above half the electron gyrofrequency in the equatorial plane (fce) for the L-shell of Kannuslehto (fce ~ 5–6 kHz). They are commonly observed at Kannuslehto, but have also been infrequently reported at other stations, sometimes under different names. Their possible common origin and manner of propagation is still under investigation. This paper unifies the nomenclature by regrouping all these waves detected at frequencies higher than the local equatorial 0.5 fce at the L-shell of observation under the name of VLF bursty-patches. While these waves have different spectral features, they appeared mostly composed of hiss bursts with durations of a few seconds to several minutes. They also show periodic features with varying periodicity and shape. They are sometimes characterized by single bursts covering very large frequency ranges of several kHz. We also give a review of the different characteristics of VLF bursty-patches observed at Kannuslehto, which at the moment, is the station with the highest observation rate. We present recent observations between 2019 and 2021.

Download Full-text

A Review of Unusual VLF Bursty-Patches Observed in Northern Finland

10.21203/rs.3.rs-582682/v1 ◽

2021 ◽

Author(s):

Claudia Martinez-Calderon ◽

Jyrki K. Manninen ◽

Jemina T. Manninen ◽

Tauno Turunen

Keyword(s):

Low Frequency ◽

Spectral Features ◽

Very Low Frequency ◽

Ground Station ◽

New Type ◽

The Moment ◽

Electron Gyrofrequency ◽

Different Characteristics ◽

Vlf Waves ◽

Large Frequency

Abstract Using numerical ﬁltering techniques allowing to reduce noise from sferics, we are able to clearly study a new type of differently structured very low frequency (VLF) waves above f = 4 kHz at the ground station of Kannuslehto in northern Finland (KAN, MLAT=64.4°N, L=5.5). These emissions are intriguing since they are detected above the local equatorial electron gyrofrequency for the L-shell of Kannuslehto (fce ~ 5- 6 kHz). They are commonly observed at Kannuslehto, but have also been infrequently reported at other stations, sometimes under different names. Their possible common origin and manner of propagation is still under investigation. This paper unifies the nomenclature by regrouping all these waves detected at frequencies higher than the local equatorial 0.5 fce at the L-shell of observation under the name of VLF bursty-patches. We also give a review of the different characteristics of VLF bursty-patches observed by Kannuslehto, which at the moment, is the station with the highest observation rate. We will present recent observations between 2019 and 2021. While these waves have different spectral features, they appeared mostly composed of hiss bursts with durations of a few seconds to several minutes. They also show periodic features with varying periodicity and shape. They are sometimes characterized by single bursts covering very large frequency ranges of several kHz.

Download Full-text

Segmentation patterns and mechanisms of genome multiplication in cultured microspores of barley

Canadian Journal of Genetics and Cytology ◽

10.1139/g84-075 ◽

1984 ◽

Vol 26 (4) ◽

pp. 475-483 ◽

Cited By ~ 24

Author(s):

C. C. Chen ◽

K. J. Kasha ◽

A. Marsolais

Keyword(s):

Gene Expression ◽

Hordeum Vulgare ◽

Structure Formation ◽

Ploidy Level ◽

Nuclear Fusion ◽

Generative Cell ◽

Low Frequency ◽

Very Low Frequency ◽

Multicellular Structure ◽

N6 Medium

Microspore segmentation in anthers of the barley line C4-13 cultured on a modified N6 medium was followed for 10 days to examine the routes to multicellular structure formation and origin of nonhaploid chromosome numbers. The first division of the uninucleate microspores gave rise to two similar nuclei or a large vegetative and a small generative cell. The two similar nuclei divided independently and both contributed to the formation of multicellular structures. Independent division of the vegetative and generative cell, and division of the vegetative cell alone resulted in two other pathways to multicellular structure formation. Nuclear fusion and endomitosis occurred in some pathways and appeared to be involved in ploidy variation. In addition, a very low frequency of fusion between the nuclei of two microspores was observed. This event may account for the occasional presence of heterozygosity in microspore-derived plants.Key words: barley (Hordeum vulgare), anther culture, androgenesis, ploidy level, nuclear fusion, endomitosis, gene expression.

Download Full-text

Complementation ofnpfmutations in diploid amoebae ofPhysarum polycephalum: the basis for a general method of complementation analysis at the amoebal stage

Genetics Research ◽

10.1017/s0016672300021935 ◽

1985 ◽

Vol 45 (1) ◽

pp. 21-35 ◽

Cited By ~ 3

Author(s):

Roger W. Anderson ◽

Philip J. Youngman

Keyword(s):

Environmental Factors ◽

Functional Groups ◽

Physarum Polycephalum ◽

Nuclear Fusion ◽

General Procedure ◽

Complementation Analysis ◽

Factors Affecting ◽

Sexual Process ◽

Mutant Strains ◽

General Method

SummaryHaploid amoebae ofPhysarum polycephalummay form plasmodia by crossing, a sexual process that involves cellular and nuclear fusions, or by selfing, an asexual process in which the development of a single amoeba into a plasmodium may involve neither cellular nor nuclear fusion. Mutant strains (npf) in which selfing is suppressed were previously assigned to several functional groups on the basis of their ability to cross with one another in certain combinations. In the present study hybrid, diploid amoebae were isolated from both crossing-compatible and incompatible mixtures ofnpfmutants. The diploid amoebae from mixtures of compatible strains readily formed plasmodia by selfing, but selfing was suppressed in the diploids from incompatible mixtures. Thus the crossing tests betweennpfmutants may be viewed as complementation tests: their results reflect the differing selfing abilities of the hybrid, diploid amoebae that formed in each mixture. Genetical and environmental factors affecting the efficiency of formation of diploid amoebae were studied, and the diploids were shown to be stable during repeated subcultures. Although diploid amoebae carrying complementingnpfmutations readily formed plasmodia by selfing at 26 δC, they could be cultured without plasmodium formation at 30 δC, a temperature that also inhibited selfing of the haploidnpf+strains. Ways are discussed of exploiting this combination of properties in a general procedure for isolating and testing diploids for dominance and complementation of amoebal mutations inP. polycephalum.

Download Full-text

The Attenuation of Very Low Frequency Brain Oscillations in Transitions from a Rest State to Active Attention

Journal of Psychophysiology ◽

10.1027/0269-8803.23.4.191 ◽

2009 ◽

Vol 23 (4) ◽

pp. 191-198 ◽

Cited By ~ 26

Author(s):

Suzannah K. Helps ◽

Samantha J. Broyd ◽

Christopher J. James ◽

Anke Karl ◽

Edmund J. S. Sonuga-Barke

Keyword(s):

Brain Activity ◽

Sampling Rate ◽

Low Frequency ◽

Future Research ◽

Adhd Symptoms ◽

Default Mode ◽

Very Low Frequency ◽

Wide Range ◽

Interference Hypothesis ◽

Mode Interference

Background: The default mode interference hypothesis ( Sonuga-Barke & Castellanos, 2007 ) predicts (1) the attenuation of very low frequency oscillations (VLFO; e.g., .05 Hz) in brain activity within the default mode network during the transition from rest to task, and (2) that failures to attenuate in this way will lead to an increased likelihood of periodic attention lapses that are synchronized to the VLFO pattern. Here, we tested these predictions using DC-EEG recordings within and outside of a previously identified network of electrode locations hypothesized to reflect DMN activity (i.e., S3 network; Helps et al., 2008 ). Method: 24 young adults (mean age 22.3 years; 8 male), sampled to include a wide range of ADHD symptoms, took part in a study of rest to task transitions. Two conditions were compared: 5 min of rest (eyes open) and a 10-min simple 2-choice RT task with a relatively high sampling rate (ISI 1 s). DC-EEG was recorded during both conditions, and the low-frequency spectrum was decomposed and measures of the power within specific bands extracted. Results: Shift from rest to task led to an attenuation of VLFO activity within the S3 network which was inversely associated with ADHD symptoms. RT during task also showed a VLFO signature. During task there was a small but significant degree of synchronization between EEG and RT in the VLFO band. Attenuators showed a lower degree of synchrony than nonattenuators. Discussion: The results provide some initial EEG-based support for the default mode interference hypothesis and suggest that failure to attenuate VLFO in the S3 network is associated with higher synchrony between low-frequency brain activity and RT fluctuations during a simple RT task. Although significant, the effects were small and future research should employ tasks with a higher sampling rate to increase the possibility of extracting robust and stable signals.

Download Full-text