Klaus Wegmann

Osmotic regulation of photosynthetic glycerol production in Dunaliella.

Abstract 1. 1. The influence of osmotically active substances on photosynthetic glycerol production and on gas exchange in Dunaliella tertiolecta was investigated. 2. 2. With increasing concentrations of NaCl, sucrose or 2-deoxy- d -glucose in the medium, the photosynthetic incorporation of [14C]bicarbonate decreases; the percentage of 14C incorporated into glycerol increases to a distinct maximum at a concentration of approx. 2.8 M NaCl, and then declines. 3. 3. Increasing the concentration of osmotic substances first causes a decline of photosynthetic oxygen evolution, then oxygen consumption, accompanied by CO2 evolution. Both show distinct maxima at approx. 2.8 M NaCl, in good agreement with the maximum of glycerol formation. The respiratory quotient indicates a fermentation process at higher osmotic pressures. 4. 4. The glycerol formation is considered to be a protective mechanism for the survival of Dunaliella in its natural habitat.

Stimulation of Orobanche crenata Seed Germination by (+)-Strigol and Structural Analogues Dependence on Constitution and Configuration of the Germinatio Stimulants

Summary The stimulation of Orobanche crenata seed germination by (+)-strigol and a series of structurally related compounds differing from (+)-strigol in constitution and/or configuration is described. Both constitution and configuration of the stimulants influence the biological activity. The absolute configuration at C-2′ (strigol numbering) seems to be of special importance.

Synchronization of Dunaliella cultures

SummaryDunaliella cells exhibit different temperature optima for photosynthesis and cell division. Using this observation a combined light-dark and highlow temperature treatment is given to synchronize cell suspensions.

Oscillations in the peroxidase-oxidase reaction: a comparison of different peroxidases

The nonlinear behavior of the peroxidase-oxidase reaction was studied using structurally different peroxidases. For the first time sustained oscillations with peroxidases other than horseradish peroxidase in a single-enzyme system were observed. All peroxidases that showed significant oxidase activity were able to generate sustained oscillations. When adjusting the overall reaction rate, either of the two modifiers 2,4-dichlorophenol or Methylene blue could be omitted from the reaction. Due to the observation of different enzyme intermediates when using different peroxidases, we conclude that the mechanisms responsible for oscillatory kinetics may vary from one peroxidase to the other.

Evidence for a mannitol cycle in Orobanche ramosa and Orobanche crenata

Summary The activities of various enzymes associated with mannitol metabolism in The activities of various enzymes associated with mannitol metabolism in Orobanche ramosa L. and Orobanche crenata Forsk. were measured both in the crude extracts of plant tissue and callus. The detection of D-mannose-6-phosphate ketol isomerase (EC 5.3.1.8), D-mannitol-l-phosphate: NADP oxidoreductase (EC 1.1.1.nn) and D-mannitol-l-phosphate phosphohydrolase (EC 3.1.3.22) activities revealed a similar pathway as postulated by Rumpho et aI. (1983) and Loescher et aI. (1992) for celery and privet, while the appearance of D-mannitol-l-phosphate:NAD oxidoreductase (EC 1.1.1.17) activity in O. callus suggests the possibility of an alternative pathway. To exclude artefacts, the above mentioned enzymes were partially purfied and further characterized. The occurrence of a low affinity D-mannitol: NAD oxidoreductase (EC 1.1.1.67)gives evidence for a mannitol cycle in the two Orobanche species. L. and Orobanche crenata Forsk . were measured both in the crude extracts of plant tissue and callus. The detection of D-mannose-6-phosphate ketol isomerase (EC 5.3.1.8), D-mannitol-1-phosphate: NADP oxidoreductase (EC 1.1.1.nn) and D-mannitol-1-phosphate phosphohydrolase (EC 3.1.3.22) activities revealed a similar pathway as postulated by Rumpho et al. (1983) and Loescher et al. (1992) for celery and privet, while the appearance of D-mannitol-1-phosphate: NAD oxidoreductase (EC 1.1.1.17) activity in O. callus suggests the possibility of an alternative pathway. To exclude artefacts, the above mentioned enzymes were partially purfied and further characterized. The occurrence of a low affinity D-mannitol: NAD oxidoreductase (EC 1.1.1.67) gives evidence for a mannitol cycle in the two Orobanche species.

Photosynthetic CO2 incorporation by isolated leaf cell protoplasts

The photosynthetic 14CO2 fixation by isolated sunflower leaf protoplasts has been investigated and the incorporation pattern has been compared with that of intact sunflower leaves. Dramatic differences have been observed only in respect to the intermediates of the photorespiratory pathway. Protoplasts accumulate glycolate, while intact leaves metabolize this compound into glyoxylate, glycine and serine. The results are discussed in comparison with the glycolate excretion by green algae. The investigations are being continued with C4 plant protoplasts.

Influence of Cycloserine on the Photosynthetic 14C Incorporation into Amino Acids in Various Algae

Summary Comparative photosynthetic 14CO2-incorporation experiments have been carried out with four unicellular alga species in the presence of equivalent nitrate or ammonia concentrations. Aminotransferase inhibition by the antibiotic cycloserine was used as a tool to distinguish between the pathways leading to various amino acids. The data provide evidence for the synthesis of alanine n Dunaliella through a pathway other than transamination.

Dynamical instabilities in a diffusion layer

We investigate the dynamics of a reaction-diffusion-convection enzyme system as a function of relevant parameters and observe reproducible types of periodic and aperiodic oscillations. These oscillations arise within a narrow diffusion layer only. Some implications for more complex reaction networks are considered

A New Model System for the Study of Complex Dynamical Enzyme Reactions. I. A Nonlinear Enzyme Reaction in a Chemical Gradient

Abstract An experimental system for the study of biochemical reaction dynamics is introduced and de scribed. A one-enzyme reaction is extended by an artificial feedback loop in an electrochemical device. Cyclic voltammetry is used to show that the reaction rate depends nonlinearly on the amount of cosubstrate offered. For some sets of fixed parameter values a damped oscillatory approach of the steady state was observed. The usefulness of the systems theoretical concepts is discussed.

Transition to Chaos via Collapse of Two-Torus in the Belousov-ZhabotinskyReaction

Abstract The transition of the dynamics of the Belousov-Zhabotinsky reaction from large peak oscillations to two-torus and chaos as a function of the flow rate is described.