14 research outputs found
Phototaxis during the slug stage of Dictyostelium discoideum: a model study
During the slug stage, the cellular slime mould Dictyostelium discoideum moves towards light sources. We
have modelled this phototactic behaviour using a hybrid cellular automata/partial differential equation
model. In our model, individual amoebae are not able to measure the direction from which the light
comes, and differences in light intensity do not lead to differentiation in motion velocity among the
amoebae. Nevertheless, the whole slug orientates itself towards the light. This behaviour is mediated by a
modification of the cyclic AMP (cAMP) waves. As an explanation for phototaxis we propose the
following mechanism, which is basically characterized by four processes: (i) light is focused on the distal
side of the slug as a result of the so-called `lens-e¡ect'; (ii) differences in luminous intensity cause
differences in NH3 concentration; (iii) NH3 alters the excitability of the cell, and thereby the shape of the
cAMP wave; and (iv) chemotaxis towards cAMP causes the slug to turn.We show that this mechanism
can account for a number of other behaviours that have been observed in experiments, such as bidirec-
tional phototaxis and the cancellation of bidirectionality by a decrease in the light intensity or the
addition of charcoal to the medium
Migration and Thermotaxis of Dictyostelium discoideum Slugs, a Model Study
Dictyostelium discoideum slugs show a pronounced thermotaxis. We have modelled the motion
of the D. discoideum slug in the absence and in the presence of a thermal gradient. Ourmodel is
an extension of the hybrid cellular automata/partial di!erential equation model, as formulated
by Savill and Hogeweg [J. theor. Biol., (1997) 184, 229-235]. The modelled slugs maintain
their shape and crawl, with a velocity depending on slug size, as found in experiments.
Moreover, they show thermotactic behaviour: independent of the initial orientation, after
some transient process, the slugs start moving along the temperature gradient. The slug
behaviour in our model is due to the collective behaviour of the amoebae. Individual amoebae
can neither respond to a shallow temperature gradient, nor show di!erentiation in motion
velocity. The behaviour is achieved by a modi"cation of the cyclic AMP waves: di!erences in
temperature alter the excitability of the cell, and thereby the shape of the cyclic AMP wave.
Chemotaxis towards cyclic AMP causes the slug to turn. We show that the mechanism still
functions at very low signal-to-noise ratios
Kilombo: a Kilobot simulator to enable effective research in swarm robotics
The Kilobot is a widely used platform for investigation of swarm robotics. Physical Kilobots are slow moving and require frequent recalibration and charging, which significantly slows down the development cycle. Simulators can speed up the process of testing, exploring and hypothesis generation, but usually require time consuming and error-prone translation of code between simulator and robot. Moreover, code of different nature often obfuscates direct comparison, as well as determination of the cause of deviation, between simulator and actual robot swarm behaviour. To tackle these issues we have developed a C-based simulator that allows those working with Kilobots to use the same programme code in both the simulator and the physical robots. Use of our simulator, coined Kilombo, significantly simplifies and speeds up development, given that a simulation of 1000 robots can be run at a speed 100 times faster than real time on a desktop computer, making high-throughput pre-screening possible of potential algorithms that could lead to desired emergent behaviour. We argue that this strategy, here specifically developed for Kilobots, is of general importance for effective robot swarm research. The source code is freely available under the MIT license
Kilombo: a Kilobot simulator to enable effective research in swarm robotics
The Kilobot is a widely used platform for investigation of swarm robotics. Physical Kilobots are slow moving and require frequent recalibration and charging, which significantly slows down the development cycle. Simulators can speed up the process of testing, exploring and hypothesis generation, but usually require time consuming and error-prone translation of code between simulator and robot. Moreover, code of different nature often obfuscates direct comparison, as well as determination of the cause of deviation, between simulator and actual robot swarm behaviour. To tackle these issues we have developed a C-based simulator that allows those working with Kilobots to use the same programme code in both the simulator and the physical robots. Use of our simulator, coined Kilombo, significantly simplifies and speeds up development, given that a simulation of 1000 robots can be run at a speed 100 times faster than real time on a desktop computer, making high-throughput pre-screening possible of potential algorithms that could lead to desired emergent behaviour. We argue that this strategy, here specifically developed for Kilobots, is of general importance for effective robot swarm research. The source code is freely available under the MIT license
Ethylene-induced differential petiole growth in Arabidopsis thaliana involves local microtubule reorientation and cell expansion
Hyponastic growth is an upward petiole movement induced by plants in response to various external stimuli. It is caused by unequal growth rates between adaxial and abaxial sides of the petiole, which bring rosette leaves to a more vertical position. The volatile hormone ethylene is a key regulator inducing hyponasty in Arabidopsis thaliana. Here, we studied whether ethylene‐mediated hyponasty occurs through local stimulation of cell expansion and whether this involves the reorientation of cortical microtubules (CMTs).
To study cell size differences between the two sides of a petiole in ethylene and control conditions, we analyzed epidermal imprints. We studied the involvement of CMT orientation in epidermal cells using the tubulin marker line as well as genetic and pharmacological means of CMT manipulation.
Our results demonstrate that ethylene induces cell expansion at the abaxial side of the‐ petiole and that this can account for the observed differential growth. At the abaxial side, ethylene induces CMT reorientation from longitudinal to transverse, whereas, at the adaxial side, it has an opposite effect. The inhibition of CMTs disturbed ethylene‐induced hyponastic growth.
This work provides evidence that ethylene stimulates cell expansion in a tissue‐specific manner and that it is associated with tissue‐specific changes in the arrangement of CMTs along the petiole