Light-Emitting-Diodes based on ordered InGaN nanocolumns emitting in the blue, green and yellow spectral range

The growth of ordered arrays of InGaN/GaN nanocolumnar light emitting diodes by molecular beam epitaxy, emitting in the blue (441 nm), green (502 nm), and yellow (568 nm) spectral range is reported. The device active region, consisting of a nanocolumnar InGaN section of nominally constant composition and 250 to 500 nm length, is free of extended defects, which is in strong contrast to InGaN layers (planar) of similar composition and thickness. The devices are driven under pulsed operation up to 1300 A/cm2 without traces of efficiency droop. Electroluminescence spectra show a very small blue shift with increasing current, (almost negligible in the yellow device) and line widths slightly broader than those of state-of-the-art InGaN quantum wells.

Substitution rate calibration of small subunit ribosomal RNA identifies chlorarachniophyte endosymbionts as remnants of green algae.

Chlorarachniophytes are amoeboid algae with chlorophyll a and b containing plastids that are surrounded by four membranes instead of two as in plants and green algae. These extra membranes form important support for the hypothesis that chlorarachniophytes have acquired their plastids by the ingestion of another eukaryotic plastid-containing alga. Chlorarachniophytes also contain a small nucleus-like structure called the nucleomorph situated between the two inner and the two outer membranes surrounding the plastid. This nucleomorph is a remnant of the endosymbiont's nucleus and encodes, among other molecules, small subunit ribosomal RNA. Previous phylogenetic analyses on the basis of this molecule provided unexpected and contradictory evidence for the origin of the chlorarachniophyte endosymbiont. We developed a new method for measuring the substitution rates of the individual nucleotides of small subunit ribosomal RNA. From the resulting substitution rate distribution, we derived an equation that gives a more realistic relationship between sequence dissimilarity and evolutionary distance than equations previously available. Phylogenetic trees constructed on the basis of evolutionary distances computed by this new method clearly situate the chlorarachniophyte nucleomorphs among the green algae. Moreover, this relationship is confirmed by transversion analysis of the Chlorarachnion plastid small subunit ribosomal RNA.

Adenylate concentration and energy charge in different thallus regions and after UV radiation in brown, red and green algae

A method was developed to extract adenine nucleotides AMP, ADP, and ATP from marine macroalgal tissue to gain information on the cellular energy charge. Quantification was carried out by high performance liquid chromatography (HPLC). Three species from the rocky shore of the island of Helgoland (German Bight) were examined: Laminaria saccharina (Phaeophyta), Chondrus crispus (Rhodophyta), and Ulva lactuca (Chlorophyta). In L. saccharina and C. crispus, the adenylate energy charge (AEC) was determined in different thallus regions. AEC varied in relation to tissue age and function. Higher AEC values typically occurred in thallus regions with meristematic activity. Furthermore, L. saccharina and U. lactuca were exposed to UV-A and elevated UV-B radiation. The AEC was calculated and the maximal quantum yield of photosystem II (Fv/Fm) was determined as indicators for UV stress. In both species, the AEC remained at high values (0.72 ± 0.04), while Fv/Fm dropped rapidly. The results show that the photosynthesis of the phaeophyte is more resistant to UV radiation than the chlorophyte.

The effect of a reduction of nitrogen and phosphorus to eutrophic and mesotrophic conditions towards silver nanoparticle (AgNP) on freshwater green algae species

We investigated the sensitivity of algae towards silver nanoparticles with OECD test medium and lower nutrient concentrations under standard test conditions to improve comparability and to exclude any other confounding factor aside nutrient levels. Two unicellular freshwater microalgae Desmodesmus subspicatus and Raphidocelis subcapitata were chosen due to their status as standard test organisms for the algae growth inhibition test and the response to changes in nutrient supply was compared. The original medium was used as the reference (standard). For the other four media, the amount of either nitrogen or phosphorus in the medium was lowered from half (50%) to one-fourth (25 %) of that of the OECD guideline, resulting in the following media: 50% N, 25% N, 50% P and 25% P medium. As test substance, the OECD reference material NM-300K was used. For this reason, the characterization of AgNP was done using DLS and Absorption spectra (UV/vis). Actual silver concentrations and ionic silver concentrations were measured at the highest test concentration used (100 µg Ag L-1) in R. subcapitata treatments only to reduce the number of samples. All tests were run according to the OECD guideline 201 with sterilized 50 mL cell culture flask. Each medium was tested using the test conditions for culturing with 3 replicates. Test concentrations for both algae species were 0, 25, 50 and 100 µg Ag L-1 for OECD, 50% P and 25% P while for both N reductions, the silver concentrations were 0, 10, 25 and 100 µg Ag L-1. Samples for determining the algal density were taken at every 24 h.