Yoshihito Mori

Photo-inhibition of chemical oscillation in the Ru (bpy)2+3-catalyzed Belousov-Zhabotinskii reaction

Abstract The wavelength dependence of photo-inhibition is reported for the Ru(bpy) 2+ 3 -catalyzed Belousov—Zhabotinskii (BZ) reaction. Use of the critical light power, P c 0 , and the relative cross section, σ R , makes it possible to discuss the inhibition mechanism quantitatively. On the basis of the observed dependences of σ R and P c 0 on wavelength and on the concentration of Ru(bpy) 2+ 3 , together with related observations of the effects of irradiation on the Br − concentration and on the BZ system without substrate, the primary step and the following processes in the inhibition phenomenon are discussed, with some newly proposed reaction schemes.

ACTION SPECTRA FOR SUPEROXIDE GENERATION AND UV AND VISIBLE LIGHT PHOTOAVOIDANCE IN PLASMODIA OF Physarum polycephalum

Abstract— The initial photochemical process leading to photoavoidance by plasmodia of an albino strain of Physarum Plasmodium was studied. Superoxide (O), detected as superoxide dismutase (SOD)‐inhibitable electron spin resonance (ESR) signal of a spin trap (tBN), was formed upon irradiation. The amount of O formed increased linearl) with log fluence rate above the threshold. The photoavoidance to radiation at wavelengths between200–800 nm also showed the similar linear relationship in log fluence rate‐response curves. Thresholds for photoavoidance and O generation agreed with each other and the action spectra showed peaks at about 260, 370, and 460 nm. Thus, active oxygen generated by photosensitization seems to trigger the UV and blue light photoavoidance.

Patterns in the distribution of intracellular ATP concentration in relation to coordination of amoeboid cell behavior in Physarum polycephalum

The Physarum plasmodium reacts tactically to external stimuli. The cell behavior of this giant amoeboid cell was studied by analysing intracellular ATP concentration. The two-dimensional (2D) spatial distribution of ATP depended on cell shape: a polar pattern for a unidirectionally migrating plasmodium, a bowl shape for a circular plasmodium, a hump shape for an oval plasmodium, or a wavy pattern for plasmodia stimulated with blue light or confined in a small chamber, etc. Local external stimulation brought about new patterns of ATP distribution. The ATP concentrations around the stimulated frontal region were reduced by about a half stimulation with KCl (repellent) or casamino acids (attractant). In both cases, migration was inhibited. Migration velocity increased almost linearly with increasing concentration of intracellular ATP above the threshold (about 20 micrograms/mg protein). Under anaerobic conditions or at low temperatures, the intracellular ATP oscillated slowly with a periodicity of about 30 min. Pattern formations in the intracellular ATP concentration and amoeboid coordination are discussed in terms of coupled chemical oscillators in a self-organizing system.

Spatio-temporal organization of intracellular ATP content and oscillation patterns in response to blue light byPhysarum polycephalum

SummaryPhototactic responses in a giant amoeboid cell ofPhysarum plasmodium were studied both by analyzing intracellular ATP content and by applying image processing for recording oscillatory changes in thickness with use of a microcomputer. The ATP content fluctuated and deviated from the initial level upon exposure to light with varying wavelength from 400 to 600 nm. The maximum decrease in the integrated value

Photoinduction and photoinhibition of chemical oscillations in the tris(2,2′-bipyridine) ruthenium (II)-catalyzed minimal bromate oscillator

\int\limits_{\text{O}}^{\text{T}} {{\text{ATP}}}

NAD(P)H oscillation in relation to the rhythmic contraction in thePhysarum plasmodium

dt with T=9 minutes occurred at the wavelength 450 nm. The ATP in a migrating plasmodium distributed twice as high in the front as in the rear. This polar pattern became unstable, and a new wavy pattern appeared by stimulating a local frontal part with blue light. In a concentrically extending plasmodium, peripheral and inside regions oscillated in opposite phase to each other. When part of this organism was exposed to light, stimulated and unslimulated regions began to oscillate in opposite phase, and phase waves propagated inward the stimulated region. And the protoplasm there became thinner, the strongest avoidance reaction occurring to 450 nm light as in ATP response. Phototactic behavior inPhysarum is discussed in terms of bifurcation in spatio-temporal organization appearing in a self-organizing system.

Oscillation of Speed of a Self-Propelled Belousov-Zhabotinsky Droplet.

Abstract The Belousov—Zhabotinsky reaction was studied for the system with two continuous-flow stirred tank reactors coupled to each other through mass transfer. The coupling strength was quantitatively controlled by changing the flow rate between the reactors with a peristaltic pump. It became clear that when the coupling between the reactors was symmetric, synchronization or entrainment with the in-phase mode was quite stable. On the other hand, the parameter space, or the basin, of the out-of-phase mode became greater with “asymmetric” coupling. Such an experimental trend is discussed in relation to the results of numerical simulations on coupled nonlinear differential equations.

Wavelength-dependent photo-inhibition of chemical oscillators: uncatalyzed oscillators with phenol and aniline as substrates

Abstract The tris (2,2′-bipyridine) ruthenium (II)-catalyzed minimal bromate oscillator is shown to exhibit the chemical oscillation similarly to the system with other catalysts. The photoresponse of the minimal oscillator has been investigated for the first time to show both induction and inhibition of sustained oscillations. It has been found that [Br−] tends to decrease not only in the photoinduction but also in the photoinhibition of chemical oscillation, in contrast to the previous view for the photoinduced pattern formation in the full Belousov-Zhabotinsky system. This result may require more detailed investigation for the latter system.