Spatial patterns in a photobiochemical system

Abstract

Illumination of a system consisting of a vertical tube containing an unstirred homogeneous suspension of thylakoids in an imposed linear concentration gradient of an electron acceptor, 2,6-dichloroindophenol, gave rise to a onedimensional banded pattern of the acceptor that evolved in a time-dependent manner. The spatial pattern was obtained only within certain parameters of the dichloroindophenol gradient and with certain concentrations of thylakoids. Various numbers of bands were obtained by varying the gradient parameters, the thylakoid concentration, or both. Pattern formation was reaction-dependent since inhibition of the water-splitting system, either by a physical (heating) or by a chemical (methylamine) method, resulted in abolition of the spatial periodicity. Obtaining the self-organized redox transition of dichloroindophenol in a gelled medium suggests that pattern formation in this system could be explained mainly by a reaction-diffusion mechanism.It has been shown from both theoretical and experimental points of view that many chemical, biological, and biochemical processes exhibit well defined spatiotemporal patterns. Pattern formation has been explained by models based on reaction-diffusion mechanisms. The reaction-diffusion theory of pattern formation was first proposed by Turing (1) and has been extensively elaborated (2, 3). Spatiotemporal breaking of symmetry has been observed with a number of chemical (4-6) and photochemical (7,8) MATERIALS AND METHODS Preparation of Thylakoids. Chloroplast thylakoids (22,23) were isolated from lettuce (Lactuca sativa var. romaine) as described by Dilley (24) with only slight modifications: the grinding solution contained 0.4 M sucrose, 20 mM HepesNaOH (pH 8.2), and 10 mM NaCI. The final pellet was resuspended in a medium consisting of 0.1 M sucrose, 10 mM Hepes-NaOH (pH 8.2), and 10 mM NaCl. Experiments were performed with fresh thylakoid preparations corresponding to an activity of 5 ,umol of 2,6-dichloroindophenol (DCIP) reduced per mg of chlorophyll per hr/ml.Experimental Production of One-Dimensional Patterns. Thylakoids corresponding to 0.57 mg of chlorophyll were suspended in a solution containing 50 mM Hepes-NaOH (pH 8.2), 0.2 M sucrose, 50 mM NaCl, and 0.83 mM MgCl2 (thylakoid suspension) and a linear gradient of DCIP was imposed as described below. Heterogeneity in the distribution of thylakoids, due to gravity, is unlikely: by using Stoke's law, we calculated (5-min induction time) that a thylakoid membrane will fall at a rate of 50 nm/sec-that is, <1% of a band thickness (2 mm).The linear gradient of the electron acceptor was formed in 15 min by mixing two thylakoid suspensions containing different concentrations of DCIP, with the use of an LKB model 11300 Ultrograd gradient mixer. Gradients are characterized by two parameters: parameter a, the concentration difference of DCIP (as mM) between the top and the bottom of the test tube, and parameter b, the lower concentration value of DCIP (as mM). A test tube (1.2 cm in diameter) was filled ...

A Reaction-Diffusion Model of ROS-Induced ROS Release in a Mitochondrial Network

“…This process can give rise to spontaneous symmetry-breaking and the appearance of self-organized spatial patterns including waves and oscillations [24]–[30]. With respect to the present model, the reaction consists of the reduction of O 2 to produce ROS (specifically O 2 .− ) driven by mitochondrial electron donors (e.g., NADH).…”

“…Reaction-diffusion theory (pioneered by Turing [23] ), as a basis for pattern formation in biological or chemical systems, emphasizes the importance of two components; an autocatalytic reaction producing a local product (mediator), and the transport of this product by diffusion away from the source. This process can give rise to spontaneous symmetry-breaking and the appearance of self-organized spatial patterns including waves and oscillations [24] – [30] . With respect to the present model, the reaction consists of the reduction of O 2 to produce ROS (specifically O 2 .− ) driven by mitochondrial electron donors (e.g., NADH).…”

Pattern formation in an immobilized bienzyme system. A morphogenetic model

“…This latter transition emerges when the non-linear properties of the implicated reactions are coupled to diffusion under welldefined boundary conditions. It has been suggested that the coupling ofthe non-linear photosynthetic reduction ofan electron acceptor [23] to diffusion in the presence of a gradient was the underlying mechanism of the symmetry change of the electron acceptor in a photobiochemical system [13].…”

“…In biochemical systems only a few experimental studies support the ability of reaction-diffusion mechanisms to produce patterns. The recent work of Aon et al [13] shows a phenomenon of pattern formation in a photobiochemical system. Those authors suggested that the non-linear reduction of an electron acceptor by photosynthetic activity, when coupled to diffusion, can trigger a symmetry change that redistributes a monotonic gradient of the electron acceptor in a banding pattern.…”

Chaotic Oscillations in a Chloroplast System Under Constant Illumination

“…Examples are oscillatory response of chlorophyll reactions to flash excitation [Eckert et al, 1979] and spatial pattern formation in a thylakoid system due to an added light sensitive acceptor [Aon et al, 1988]. Measurements on intact organisms suggest periodicity of the order of some minutes in photosynthetic reactions [Laisk, 1977].…”