Die Regulation des Photosyntheseapparates bei Chlorogonium elongatum Dangeard unter dem Einfluß von Licht und Acetat

Sixty years in algal physiology and photosynthesis

This personal perspective records research experiences in chemistry and biology at four German universities, two before and two after World War II. The research themes came from cytophysiology of green unicellular algae, in particular their photosynthesis. The function of inorganic ions in photosynthesis and dark respiration was investigated at different degrees of specific mineral stress (deficiencies), and the kinetics of recovery followed after the addition of the missing element. Two types of recovery of photosynthesis were observed: indirect restitution via growth processes and immediate normalisation. From the latter case (K(+), phosphate, Mn(++)) the effect of manganese was emphasized as its role in photosynthetic O2 evolution became established during our research. Other themes of our group, with some bearing on photosynthesis were: synchronization of cell growth by light-dark change and effects of blue (vs. red) light on the composition of green cells. Some experiences in connection with algal mass cultures are included. Discussion of several editorial projects shows how photosynthesis, as an orginally separated field of plant biochemistry and biophysics, became included into general cell physiology and even ecophysiology of green plants. The paper contains an appreciation of the authors' main mentor Kurt Noack (1888-1963) and of Ernst Georg Pringsheim (1881-1970), founder of experimental phycology.

The effects of light quality and intensity on the synthesis of ribulose-1,5-bisphosphate carboxylase and its mRNAs in the green alga Chlorogonium elongatum

In the green alga Chlorogonium elongatum the promoting effect of light on the synthesis of ribulose bisphosphate carboxylase/oxygenase (RuBPCase) is mainly caused by blue light of wavelengths between 430 nm and 510 nm, with a maximum effect at about 460 nm. Blue light also causes an increase in the amounts of the mRNAs for the large and the small subunits of the enzyme. Furthermore, the concentration of RuBPCase is affected by the light energy fluence rate. The rate of synthesis as well as the maximal obtainable concentration of the enzyme are functions of the light energy fluence rate up to 26 W·m(-2). No further increase occurs beyond that intensity. The quantity of irradiation also alters the concentrations of the subunit mRNAs. The results indicate that the changes in the mRNA levels are the major regulatory steps in the light-dependent synthesis of the RuBPCase enzyme.

Isocitrate lyase of the alga Chlorogonium elongatum: Immunological quantification in relation to growth conditions

Isocitrate lyase (EC 4.1.3.1) from the acetate flagellate Chlorogonium elongatum was studied in relation to growth conditions. In cells growing heterotrophically or photoheterotrophically with acetate (2 g · l(-1)) specific activities of 0.453 and 0.335 μmol glyoxylate · min(-1) · mg(-1) protein, respectively, were found in the cell-free extracts. The malate synthase activity of heterotrophically grown Chlorogonium cells was found to be 0.572 nmol · min(-1) · mg(-1) protein. In the presence of inhibitors acting on transcription and translation there was no increase in isocitrate lyase activity; this would indicate that the enzyme was synthesized de novo in response to changing conditions in the surroundings. Using an enzyme immunoassay it was shown that the activity and amount of enzyme rose concomitantly when the cells were supplied with acetate, irrespective of whether they had been cultivated photoheterotrophically or heterotrophically on acetate.

Pyruvate degradation via pyruvate formate-lyase (EC 2.3.1.54) and the enzymes of formate fermentation in the green alga Chlorogonium elongatum

Formate was formed in extracts of Chlorogonium elongatum via direct cleavage of pyruvate by a pyruvate formate-lyase (PFL, EC 2.3.1.54). The conversion of PFL to the catalytically active form required S-adenosylmethionine, ferric (2+), photoreduced deazariboflavin as reductant, pyruvate as allosteric effector and strict anaerobic conditions. At the optimum pH (pH 8.0), PFL catalyzed formate formation, pyruvate synthesis and the isotope exchange from [(14)C]formate into pyruvate with rates of 30.0, 1.5 and 1.2 nmol min(-1) mg(-1) protein, respectively. Treatment of the active enzyme with O2 irreversibly inactivated PFL activity (half-time 2 min). In addition to PFL, the activities of phosphotransacetylase (EC 2.3.1.8), acetate kinase (EC 2.7.2.1), aldehyde dehydrogenase (CoA acetylating, EC 1.2.1.10) and alcohol dehydrogenase (EC 1.1.1.1) were also detected in extracts of C. elongatum. The occurrence of these enzymes indicates pyruvate degradation via a formate-fermentation pathway during anaerobiosis of algal cells in the dark.

Regulation of the synthesis of ribulose-1,5-bisphosphate carboxylase and its subunits in the flagellate Chlorogonium elongatum. Different levels of translatable messenger RNAs for the large and the small subunits in autotrophic and heterotrophic cells as determined by immunological techniques

Poly(A)-rich and poly(A)-free RNAs were isolated from autotrophic and heterotrophic cells of the phytoflagellate Chlorogonium elongatum and translated in an mRNA-depleted reticulocyte lysate system. Immunoprecipitation methods were improved to detect large and small subunits of the chloroplast enzyme ribulose-1,5-bisphosphate carboxylase synthesized in vitro. Large-subunit polypeptides were shown to be the translation products of poly(A)-free RNA having the same molecular weight as large subunits made in vivo. Small-subunit polypeptides were synthesized when poly(A)-rich RNA was used as a template. They were made in vitro as a precursor, with an Mr about 6000 larger than mature small subunits. Cells growing heterotrophically in the dark with acetate are provided with lower levels of mRNA activities for the large and the small subunits is at least partially controlled by the amounts of translatable mRNAs.

[Distribution of microbody enzymes from Chlamydomonas on sucrose gradients]

The crude homogenate of cells from Chlamydomonas reinhardii was placed on a linear gradient from 30% to 60% sucrose and centrifuged for 4 hours at 60 000 g. After fractionation of the gradient the distribution of enzymes was determined. Hydroxypyruvate reductase and glycolate dehydrogenase, two markers for peroxisomes, appeared with one sharp peak at density 1.185 g/cm(3) within the gradient. Twenty-five percent of the hydroxypyruvate reductase was particulate and 75% was found as solubles in the top fractions. The peaks of both enzymes matched exactly the peak of the cytochrome oxidase which is a marker for mitochondria. The profile for malate dehydrogenase was the same as that for hydroxypyruvate reductase. Catalase, however, showed two peaks. One coincided with the peak of cytochrome oxidase and the other appeared at density 1.22 g/cm(3). More than 50% of the catalase moved into the gradient during centrifugation.

[Studies on the uptake of glycolate by Chlorogonium]

The alga Chlorogonium was cultured either heterotrophically or autotrophically under different partial pressures of CO2 by aerating with pure air of air enriched with 2% CO2. Cells were harvested in the logarithmic phase, transferred to phosphate buffer containing 0.01 M 1C(14)-glycolate and incubated with shaking in the dark. Under these conditions the rate of glycolate uptake was higher when the cells had been grown in the light. Cells grown in the light at the lower CO2-concentration took up more glycolate than those grown with 2% CO2. Approximately 90% of the radioactivity taken up with the glycolate was released as CO2. The radioactivity remaining in the algae was somewhat higher in those cells which had been cultured heterotrophically or autotrophically under air than in cells grown autotrophically under air enriched with 2% CO2.Addition of glycolate increased the uptake of oxygen by the cells. The consumption of the oxygen was quantitatively correlated to the uptake of glycolate.