Wolfram Braune

Ultrastructural and chemical changes in the cell wall of Haematococcus pluvialis (Volvocales, Chlorophyta) during aplanospore formation

Changes in the ultrastructure and chemistry of the cell wall of the unicellular volvocalean green alga Haematococcus pluvialis were investigated during the transformation of flagellates into aplanospores. The motile biflagellated state exhibited a distinct gelatinous extracellular matrix. Its ultrastructure resembled the typical volvocalean multilayered architecture with a median tripartite crystalline layer. The transformation into the non-motile cell state was characterized by formation of a new layer, a primary wall, within the extracellular matrix. During this process, the initial extracellular matrix remained intact except for the outer layers of the tripartite crystalline layer, which decomposed. Further morphogenesis of the aplanospore resulted in the formation of a voluminous multilayered cell wall. A trilaminar sheath was formed inside the primary wall and the innermost and thickest part was an amorphous secondary wall, consisting mostly of a mannan. Results obtained by staining with the fluorescent dye primuline as well as by acetolysis suggest the occurrence of sporopollenin-like material (algaenan) within the trilaminar sheath of the aplanospore cell wall. The primary wall and the outer remnants of the extracellular matrix disintegrated as the aplanospores aged, and were completely absent in the resting cell state.

Functional aspects of secondary carotenoids in Haematococcus lacustris (Volvocales). III: Action as a Sunshade'

We investigated the protection from photoinhibition by different developmental stages of Haematococcus lacustris [Girod] Rostafinski using chlorophyll fluorescence measurements of single cells and suspensions. An overall correlation between higher cellular content of secondary carotenoids and the capacity to withstand excessive irradiation was observed in flagellated cells and aplanospores of H. lacustris. Low‐light‐reversible spreading of extra‐chloroplastic secondary carotenoids occurred in the periphery of the cell during strong irradiation. This process resulted in increased shading of the cup‐shaped chloroplast as demonstrated by a decrease in chlorophyll fluorescence. Extrachloroplastic accumulation of secondary carotenoids in H. lacustris can be interpreted as a specific adaptation to habitats that exhibit strong insolation.

C-Phycocyanin—the main photoreceptor in the light dependent germination process of Anabaena akinetes

Action spectra obtained for the light dependent germination process of Anabaena akinetes, as determined according to different photon flux rate response relationships (24 wavelengths between 400 nm and 750 nm) uniformly demonstrate a maximum between 620 nm and 630 nm. Thus the most active spectral range for the germination process coincides with the maximum of the light absorption by C-phycocyanin. Sine germination is only slightly impaired when electron transport is blocked by DCMU, the formation of photosynthetic products as prerequiste of germination is rather unlikely. The participation of phycocyanin in cyclic photophosphorylation and in other photochemical processes is discussed with respect on possible participation in stimulating. There are indications of different flux rate and wavelength dependencies of germination and growth, respectively.

Secondary carotenoid accumulation in flagellates of the green alga Haematococcus lacustris

The combination of nitrogen deprivation and increased cultivation light intensity resulted in the synthesis of secondary carotenoids in flagellates of Haematococcus lacustris. The pigment pattern was characterized by high-pressure liquid chromatography analysis during the accumulation period and in response to inhibitors of carotenoid biosynthesis (diphenylamine, norflurazon and tetcyclacis). Diphenylamine treatment resulted in (i) a decrease in ketocarotenoids and (ii) an accumulation of b-carotene and zeaxanthin due to inhibition of the bcarotene oxygenase. Our results indicate that astaxanthin synthesis in H. lacustris follows the biosynthetic pathway elucidated in the marine bacterium Agrobacterium aurantiacum.

Influence of Nickel on the Green Alga Haematococcus lacustris Rostafinski in Phases of its Life Cycle

Summary The influence of nickel (NiSO 4 6H 2 0; 1 and 100 μm) on the phases of germination of the resting cells (aplanospores), cell division in the flagellate stage, and during aging (formation of aplanospores) in Haematococcus lacustris was investigated. Nickel at the 1 μM-concentration (commonly found in aquatic biotopes) had no effects on the parameters tested. However, 100 μM Ni reduced the germination rate and the protein and chlorophyll contents it caused slight inhibition of the phototaxis in flagellates, but was without effects on the carotenoid and carbohydrate contents and on the primary photochemistry during the germination of aplanospores. In the other phases (cell division and formation of aplanospores) the toxic effects were particularly pronounced: 100 μM Ni strongly decreased the growth rate, pigment content, photosynthesis, and the number of motile cells; it completely inhibited the formation of aplanospores, while the velocity of movement in flagellates and the protein and carbohydrate contents were not or only slightly influenced.

Structural aspects of akinete germination in the cyanobacterium Anabaena variabilis

Electronmicroscopical investigations of light activated akinetes in different phases before outgrowth of the germinating cell showed two alterations in the akinete envelope, obviously in connection with the germination process. After induction of germination the akinetes show formation of an expanding more or less electron dense layer between the outer cell wall layer (outer membrane, LIV) and the condensed part of the akinete coat (the transformed sheath of the vegetative cell). Between this new formed layer and the mentioned part of the akinete coat thick “laminar layers” are deposited which contain alternately electron dense and electron transparent strata. The expanding layer is assumed to be a mucous layer which acts as swelling body causing, after bursting of the layered shell, the expulsion of the germinating cell in the manner characteristic for Anabaena variabilis.

Impact of UV-B Radiation on 15N-Ammonium and 15N-Nitrate Uptake by Haematococcus lacustris (Volvocales). I. Different Response of Flagellates and Aplanospores

Summary The freshwater green alga Haematococcus lacustris accumulates 15 N given as 15 N-NH 4 + to a higher extend than with 15 N-NO 3 − . Special attention was focused to investigate the influence of UV-B radiation on the 15 N-uptake. UV-B (1.25 W m −2 ) was applied additionally to the standard light conditions (8 W m −2 ) and nitrogen incorporation was determined for 5 hours during and after the irradiation period. The response of two different developmental stages of the cells on the UV-B-load (green flagellates and red coloured aplanospores), each in two different metabolic conditions (nitrogen-starved dark precultivated and nitrogen-supplied light precultivated cells, respectively) were examined. Results indicate (1) UV-B inhibits the incorporation of 15N-nitrogen in both cell types. (2) The degree of inhibition in aplanospores is generally lower than in the flagellates. This principle is valid also in activated aplanospores. (3) Activated cells of both types show a higher degree of inhibition in nitrate an ammonium uptake than cells precultivated under starvation. (4) Nitrogen incorporation is also inhibited when UV-B-radiation is applied before addition of the 15 N-labelled compounds; Different uptake kinetics derived from these experiments are discussed with respect to the possible target of UV-B-influence.

Phototactic responses in Haematococcus lacustris and its modification by light intensity and the carotenoid biosynthesis inhibitor norflurazon

At fluence rates below 45 W· m-2 cells of the flagellate stage of Haematococcus lacustris react only positively phototactically with a rather high degree of orientation (indicated by r values up to 0.66 with the Rayleigh test). The directedness of orientation decreases with decreasing irradiance. The degree of directedness of the phototactic response depends on the intensity of preirradiation: Low light intensity applied after strong light application results in a “dark reaction” (low r values), low light given after darkness stimulates a rather high degree of directedness of positive phototaxis. Weak blue light (λ=483 nm; 0.4 W · m-2) stimulates positive phototactic response, whereas comparable red light (λ=658 nm; 0.5 W · m-2) does not.Cells which were grown in a medium containing 10-4 M Norflurazon (effective in inhibition of carotenoid biosynthesis) although maintaining motility completely lose the ability to react positively phototactically. The possible role of carotenoids in the phototactic orientation is discussed.

Impact of UV-B radiation on 15N-Ammonium and 15N-Nitrate uptake by Haematococcus lacustris (volvocales) II. The influence of a recovery period

Summary The influence of UV-B irradiation (280–320 nm; 0.5 to 5 hours; 1.25 Wm −2 ) applied at the beginning of a 12 hours polychromatic irradiated («white light recovery») period (8 Wm −2 PAR) on the accumulation of 15 N-ammonium and 15 N-nitrate, the content of protein and amino acids/amides was investigated in different developmental stages (flagellates/aplanospores) and pre-cultivation variants (N-supplied/N-starved) of the freshwater green alga Haematococcus lacustris . In a further series of experiments the consequences of a white light recovery period, extended to 24 hours, on the UV-B influenced 15 N-accumulation was examined. Main results indicate: (1) The 12 hours recovery period does not abolish the uptake inhibition by UV-B, but lowers significandy the scope of it (i.e. the decrease of the N-accumulation; exception: N-starved (predark, -N) precultivated flagellates). (2) The cell type specific UV-B dose dependent course of the inhibition was similar to that without a recovery period (stronger in flagellates than in aplanospores). (3) An extension of the recovery period to 24 hours altered drastically the response of the flagellates (stimulated 15N uptake after UV-B irradiation, dose-dependent) but not in the aplanospores. (4) Proteins and pools of free amino acids/amides were specific influenced by the UV-B treatment and the recovery period, respectively. Also the relative content in single amino acids changed differendy on the UV impact, dependent on cell type, pre-treatment and if a recovery was included or not. Also without mentioning the UV-B impact, significant differences in the content of single amino acids were observed between flagellates and aplanospores: Arginine and glutamate were higher in aplanospores, whereas the opposite was found for serine.

Pseudococcomyxa adhaerens Korshikov?eine an extreme Lebensbedingungen angepate kokkale Grnalge

ZusammenfassungMassenentwicklung von Pseudococcomyxa adhaerens Korshikov, einer kleinen kokkalen Chlorophycee, trat wiederholt spontan in Vorratsgefäßen für destilliertes Wasser auf. Eine Übertragung der Algen in reine MgSO4-Lösungen (geprüft bis zu 24%) geschah ohne Schaden für den Organismus, das Wachstum war sogar stimuliert. Eine hohe cH+ und sehr geringe Lichtintensitäten sind Bedingung für eine gute Entwicklung der Algen unter diesen Voraussetzungen.Massenentwicklung von Pseudococcomyxa adhaerens Korshikov, einer kleinen kokkalen Chlorophycee, trat wiederholt spontan in Vorratsgefasen fur destilliertes Wasser auf. Eine Ubertragung der Algen in reine MgSO4-Losungen (gepruft bis zu 24%) geschah ohne Schaden fur den Organismus, das Wachstum war sogar stimuliert. Eine hohe cH+ und sehr geringe Lichtintensitaten sind Bedingung fur eine gute Entwicklung der Algen unter diesen Voraussetzungen.