In this paper experimental results of investigation of the oscillations in a photosynthetic system are presented and a model for their interpretation is suggested. Periodicities in photosynthetic systems detected in earlier studies by physical chemical methods can be also detected by means of recording the potential difference between two point electrodes. The observed dependences demonstrate a wide range of various types of behaviour of the system, working, e.g. in periodic, quasiperiodic, chaotic or 'pulse' regimes. Since the until-now-used 2-dimensional theoretical model, based on the existence of two dominant autocatalytical processes, appeared not to be sufficient for explaining such types of the regimes, a generalized 3-dimensional autocatalytical model is suggested, which is able to explain all the above mentioned photosynthetic regimes.

Coherent glycolytic oscillations in Saccharomyces cerevisiae are a multicellular property induced by addition of glucose to a starved cell population of sufficient density. However, initiation of oscillations requires an additional perturbation, usually addition of cyanide. The fate of cyanide during glycolytic oscillations has not previously been studied, and is the subject of the present paper. Using a cyanide electrode, a substantial decrease in cyanide concentration was observed. In the pH range 6-7, we found experimentally that the electrode behaves reasonably well, provided changes in pH are taken into account. To our knowledge, use of a cyanide electrode to study cyanide dynamics in living biological systems is new. Cyanide was found to enter starving yeast cells in only negligible amounts, and did not react significantly with glucose. Thus, cyanide consumption must be explained by reactions with glycolytic intermediates and evaporation. Evaporation and reaction with the signalling substance, extracellular acetaldehyde (ACA x ) only explains the observed cyanide removal if [ACA x ] is improbably high. Furthermore, differences in NADH traces upon cyanide addition before or after glucose addition strongly suggest that cyanide also reacts with intracellular carbonyl-containing metabolites. We show that cyanide reacts with pyruvate (Pyr) and dihydroxyacetone phosphate in addition to ACA, and estimate their rate constants. Our results strongly suggest that the major routes of cyanide removal during glycolysis are reactions with pyruvate and ACA. Cyanide removal by all carbonyl-containing intermediates led to a lower mean [ACA x ], thereby increasing the amplitude of [ACA x ] oscillations. Database The mathematical model described here has been submitted to the JWS Online Cellular Systems Modelling Database and can be accessed at http://jjj.biochem.sun.ac.za/database/hald/ index.html free of charge.

We show that nonlinear, aperiodic oscillatory behavior can be observed in a chloroplast system by measuring the absorption of light. This behavior depends on illumination of the system with light which is absorbed by chlorophyll. The oscillations can be stopped by addition of acetone indicating that chemical reactions are involved. These observations confirm the role of photosynthesis. The effect of stirring and the statistics of the oscillating part of the spectrum suggest that the buoyancy of oxygen bubbles formed during photosynthesis is an important part of the mechanism.

Temporal and spatial structures in the Belousov-Zhabotinskii systems in constant electric and strong magnetic fields are studied in this paper. Unlike a random generation of chemical wave center in a system without the influence of an electromagnetic field we have observed that only one wave forms in the presence of electric and magnetic fields of suitable intensity and induction. Its speed of propagation depends on the connected fields. A theory of this phenomenon has been developed and the obtained results are in a good agreement with experimentally measured dependences of the temporal period of chemical waves on electric field intensity and magnetic field induction.