Hendrik Schubert

The genus Laminaria sensu lato : recent insights and developments

This review about the genus Laminaria sensu lato summarizes the extensive literature that has been published since the overview of the genus given by Kain in 1979. The recent proposal to divide the genus into the two genera Laminaria and Saccharina is acknowledged, but the published data are discussed under a ‘sensu lato’ concept, introduced here. This includes all species which have been considered to be ‘Laminaria’ before the division of the genus. In detail, after an introduction the review covers recent insights into phylogeny and taxonomy, and discusses morphotypes, ecotypes, population genetics and demography. It describes growth and photosynthetic performance of sporophytes with special paragraphs on the regulation of sporogenesis, regulation by endogenous rhythms, nutrient metabolism, storage products, and salinity tolerance. The biology of microstages is discussed separately. The ecology of these kelps is described with a focus on stress defence against abiotic and biotic factors and the role of Laminaria as habitat, its trophic interactions and its competition is discussed. Finally, recent developments in aquaculture are summarized. In conclusion to each section, as a perspective and guide to future research, we draw attention to the remaining gaps in the knowledge about the genus and kelps in general.

Long-Term Response toward Inorganic Carbon Limitation in Wild Type and Glycolate Turnover Mutants of the Cyanobacterium Synechocystis sp. Strain PCC 6803

Concerted changes in the transcriptional pattern and physiological traits that result from long-term (here defined as up to 24 h) limitation of inorganic carbon (Ci) have been investigated for the cyanobacterium Synechocystis sp. strain PCC 6803. Results from reverse transcription-polymerase chain reaction and genome-wide DNA microarray analyses indicated stable up-regulation of genes for inducible CO2 and HCO3− uptake systems and of the rfb cluster that encodes enzymes involved in outer cell wall polysaccharide synthesis. Coordinated up-regulation of photosystem I genes was further found and supported by a higher photosystem I content and activity under low Ci (LC) conditions. Bacterial-type glycerate pathway genes were induced by LC conditions, in contrast to the genes for the plant-like photorespiratory C2 cycle. Down-regulation was observed for nitrate assimilation genes and surprisingly also for almost all carboxysomal proteins. However, for the latter the observed elongation of the half-life time of the large subunit of Rubisco protein may render compensation. Mutants defective in glycolate turnover (ΔglcD and ΔgcvT) showed some transcriptional changes under high Ci conditions that are characteristic for LC conditions in wild-type cells, like a modest down-regulation of carboxysomal genes. Properties under LC conditions were comparable to LC wild type, including the strong response of genes encoding inducible high-affinity Ci uptake systems. Electron microscopy revealed a conspicuous increase in number of carboxysomes per cell in mutant ΔglcD already under high Ci conditions. These data indicate that an increased level of photorespiratory intermediates may affect carboxysomal components but does not intervene with the expression of majority of LC inducible genes.

Disruption of a Synechocystis sp. PCC 6803 gene with partial similarity to phytochrome genes alters growth under changing light qualities

A gene that may encode a novel light sensing histidine protein kinase, designated plpA (phytochrome‐like protein), was isolated from the cyanobacterium Synechocystis sp. PCC 6803. The 200 COOH‐terminal amino acids of the gene product show homology with conserved domains of several bacterial histidine kinases and the ethylene response gene etr1 of Arabidopsis, whereas its central region is similar to the chromophore attachment site of plant phytochromes. Interruption or partial deletion of plpA yielded mutants unable to grow under blue light.

Parasitic apicomplexans harbor a chlorophyll a-D1 complex, the potential target for therapeutic triazines

Ultrastructural evidence is presented for the presence of plastid-like organelles inToxoplasma gondii, Sarcocystis muris, Babesia ovis, andPlasmodium falciparum. In addition, it was shown that merozoites ofT. gondii contain protochlorophyllidaea and traces of chlorophylla bound to the photosynthetic reaction centers I PS I and PS II. ApsbA gene was isolated from merozoites ofS. muris by the polymerase chain reaction (PCR). Partial sequencing of the PCR product revealed that the herbicide-binding region is highly conserved. Therefore, it is likely that the sensitivity of apicomplexans to the herbicide toltrazuril depends on the interaction of the herbicide with the D1 protein of the photosynthetic reaction center of the parasites organelles.

Daily course of photosynthesis and photoinhibition in Chondrus crispus (Rhodophyta) from different shore levels

Photoinhibition of photosynthesis in the red alga Chondrus crispus from different shore levels was investigated under laboratory and field conditions. The underwater light climate at Roscoff (French Atlantic coast), characterized by transmittance spectra, was shown to be intermediate between Jerlov coastal type 1 and oceanic type III. Chondrus crispus thalli were collected at four depths (3.5–8.5 m below high tide level) and exposed to daily courses of artificial and natural light. Filters were used to discriminate between the effects of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) under the photoinhibitory treatments. In the presence of natural UVR, photoinhibition at midday was increased by up to 60%. Recovery from photoinhibition was measured at different times throughout the light stress. Recovery kinetics differed between morning and early afternoon in all treatments, and were dependent on the light dose. Whereas biphasic kinetics were observed in all treatments in the mo...

Effects of Adaptation to Different Salt Concentrations on Photosynthesis and Pigmentation of the Cyanobacterium Synechocystis sp. PCC 6803

Summary After adaptation of Synechocystis sp. PCC 6803 to different salt concentrations the growth optimum was found to be around 342 mM NaCl. At this salinity photosynthesis per cell-volume and the contents of chlorophyll and phycocyanin showed the highest values. Based on pigment contents maximal photosynthesis was measured in cells adapted to the highest salt concentration of 1026 mM NaCl. Therefore, it was concluded that in less pigmented cells the absorbed light could be more efficiently used for photosynthesis than in cells with excess pigment contents. In fluorescence emission spectra, inefficient energy transfer between phycobilisomes and chlorophyll was measured in cells rich in phycocyanin growing at 342 mM NaCl. Adaptation to higher salt concentrations also led to changes in the content and composition of the carotenoids. In cells adapted to 1026 mM NaCl the highest contents of carotenoid especially echinenone and glycosidic carotenoids, were detected.

Microplastic concentrations in beach sediments along the German Baltic coast

The contamination with microplastic particles and fibres was evaluated on beaches along the German Baltic coast. Sediments were sampled near the Warnow and Oder/Peene estuaries, on Rügen island and along the Rostock coast to derive possible entry pathways. Seasonal variations were monitored along the Rostock coast from March to July 2014. After density separation in saline solution, floating particles were found to be dominated by sand grains. Water surface tension is shown to be sufficient to explain floatation of grains with sizes less than 1.5mm. Selecting intensely coloured particles and fibres, we find lower limits of the microplastic concentrations of 0-7 particles/kg and 2-11 fibres/kg dry sediment. The largest microplastic contaminations are measured at the Peene outlet into the Baltic Sea and in the North Sea Jade Bay. City discharges, industrial production sites, fishing activity and tourism are the most likely sources for the highest microplastic concentrations.

ACCLIMATION OF PALMARIA PALMATA (RHODOPHYTA) TO LIGHT INTENSITY: COMPARISON BETWEEN ARTIFICIAL AND NATURAL LIGHT FIELDS

The acclimation of the photosynthetic apparatus of Palmaria palmata (L.) to light intensity was examined in the field and under laboratory conditions. Algae from 3 different shore levels and from laboratory cultures adapted to 6 different photon flux densities were compared. This was done on the basis of light doses, which were delivered by different light regimes in the field and in the laboratory. Laboratory samples were adjusted to constant photon flux densities between 7 and 569 μmol photons·m−2·s−1 in a 16:8 light:dark photoperiod. Under field conditions the daily amplitudes reached up to approximately 2000 μmol photons·m−2·s−1 within a natural daily light course. Over the course of 14 days the light doses resulting from those different regimes are similar for both treatments. An increasing growth rate per day with increasing light doses was observed in the laboratory. Growth was saturated at 113 mol photons·m−2·14 d−1. Light saturation points (Ek) of photosynthesis increased with increasing light doses for both field and laboratory samples, and all Ek values were significantly related to the growth light dose. A correlation between fresh weight‐related lutein content and growth light dose was found for laboratory samples only, whereas the lutein:chlorophyll a (chl a) ratio was strongly correlated with Ek for laboratory and field samples. The content of chl a and phycoerythrin (PE) per fresh weight decreased significantly with increasing light doses under field conditions. Simultaneously, the PE:chl a ratio increased, whereas this ratio was not influenced by laboratory treatments. The correspondence of Ek values for field and laboratory treatments indicated that they were affected mainly by light dose. However, the variability in pigmentation was mainly dependent on temporal variability in light intensity (the amplitude of variations in incident light).

Downstream changes in phytoplankton composition and biomass in a lowland river–lake system (Warnow River, Germany)

To determine longitudinal changes in phytoplankton composition and biomass in the Warnow River (Germany), single water parcels were followed during their downstream transport in August and October 1996 and April 1997. In summer, the phytoplankton assemblage was dominated by centric diatom and cyanobacteria species. Stephanodiscus hantzschii, Pseudanabaena limnetica, Planktothrix agardhii and Aulacoseira granulata var. angustissima were the most frequent species. In autumn, small centric diatoms dominated the whole river course. Irrespective of the season, in the fluvial lakes of the upper river, a substantial increase of phytoplankton biomass was observed. Shallow upstream river stretches were associated with large biomass losses. In the deep, slow flowing lower regions, total biomass remained constant. Longitudinal changes in biomass reflected downstream variations in flow velocity and river morphology. Cyanobacteria, cryptophytes and diatom species were subjected to large biomass losses along fast flowing, shallow river sections, whereas chlorophytes were favoured. Diatoms and cryptophytes benefited from low flow velocity and increased water depth in the downstream river. Changes in water depth and flow velocity have been found as key factors that cause the longitudinal differences in phytoplankton composition and biomass in small rivers.

Macroalgal diversity along the Baltic Sea salinity gradient challenges Remane's species-minimum concept

Remanes species-minimum concept, which states that the lowest number of taxa occurs at the horohalinicum (5-8psu), was tested by investigating macroalgal diversity on hard substrates along the natural salinity gradient in the Baltic Sea. Field data on species occurrence and abundance were collected by SCUBA diving along 10 transects of the Finnish, Swedish and German coasts, covering a salinity range from 3.9 to 27psu. Macroalgal species numbers declined steadily with salinity, decreasing until 7.2psu was reached, but in the horohalinicum, a marked reduction of species number and a change in diversity were indicated by the Shannon index and evenness values. The non-linear decrease in macroalgal diversity at 5-8psu and the lack of increase in species numbers at salinities below 5psu imply a restricted applicability of Remanes species-minimum concept to macroalgae.