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The distribution of photosystem I (PS I) and photosystem II (PS II) in a primitive green alga Tetraselmis subcordiformis, which belongs to Prasinophyceae and does not have grana in its chloroplast, was studied by immunoelectron microscopy. Two PS I antibodies were used: one against a PS I component of maize, the other against the 60 and 62 KDa PS I reaction centre proteins of the cyanobacterium Synechococcus elongatus. Both antibodies showed that 76-78% of the labelling is on the appressed thylakoid membranes and only 22-24% is located on the unappressed membranes. Use of antiserum against cp-47 of PS II from S. elongatus also gives 76% of the labelling on appressed thylakoid membranes and 24% on unappressed thylakoid membranes. Cytochemical detection of PS I activity by the photooxidation of 3,3$ sp prime$-diaminobenzidine and of PS II activity by the photoreduction of distyryl nitroblue tetrazolium chloride also revealed that PS I and PS II activities exist on both types of thylakoid membranes. Therefore, our results indicate that the distribution of PS I and PS II in green algae may differ from that in higher plants.

Epilithic biofilms were monitored for potential impacts of an experimental rainbow trout aquaculture operation at the Experimental Lakes Area in northwestern Ontario, Canada. Metabolic and particulate samples were collected from the middle littoral zone of the experimental and reference lakes before and during the aquaculture operation. Phosphorus stocks in the experimental lake (epilimnetic and epilithic) increased as a result of both food waste and fish excretion. These cumulative P inputs were predicted to increase epilithic biomass and productivity, cause major compositional changes in the dominant groups and increase epilithic algal toxin production (microcystins). However, no major aquaculture-related changes in algal biomass, productivity, toxins or group dominance were observed in the epilithon. The only observed changes occurred at the species-level. These species-level changes were transient but did allude to an ecosystem reacting to stress.

No description available.

Epilithic biofilms were monitored for potential impacts of an experimental rainbow trout aquaculture operation at the Experimental Lakes Area in northwestern Ontario, Canada. Metabolic and particulate samples were collected from the middle littoral zone of the experimental and reference lakes before and during the aquaculture operation. Phosphorus stocks in the experimental lake (epilimnetic and epilithic) increased as a result of both food waste and fish excretion. These cumulative P inputs were predicted to increase epilithic biomass and productivity, cause major compositional changes in the dominant groups and increase epilithic algal toxin production (microcystins). However, no major aquaculture-related changes in algal biomass, productivity, toxins or group dominance were observed in the epilithon. The only observed changes occurred at the species-level. These species-level changes were transient but did allude to an ecosystem reacting to stress.

Fucoid algae live in the intertidal region where they experience daily fluctuations in light and external osmotic environment. High light, especially in combination with ultraviolet (UV) radiation and hyper-osmotic stress affected the cellular physiology of Fucus embryos. Two photoinhibition responses were recognised. Firstly, a rapid decline of the photosystem II (PSII) efficiency, linked with the operation of the xanthophyl cycle, followed by a slower decline correlated with reactive oxygen species (ROS) production. As a result of enhanced ROS production, a slower repair of the PSII efficiency was observed, particularly with increased UV-B doses. Development of the embryos was transiently affected by UV-B. The cellular signal transduction pathway during hyper-osmotic stress was investigated. ROS production in response to hyperosmotic stress comprised two distinct components. The first ROS component coincided closely with the origin of a Ca2+ wave in the peripheral cytosol at the growing cell apex, had an extracellular origin, and was necessary for the Ca2+ wave. Patch clamp experiments showed that a non-selective cation channel was stimulated by H2O2, and may underlie the initial cytosolic Ca2+ elevation. The spatio-temporal pattern of the Ca2+ wave was thus determined by peripheral ROS production. The second, later ROS component localised to the mitochondria and was a direct consequence of the Ca2+ wave. The first, but not the second component was required for short-term adaptation to osmotic stress, probably through the activity of cell wall bromoperoxidases. Mitogen-activated protein kinases may be involved in the hyper-osmotic stress response downstream or independently of the mitochondrial ROS production.

Highly branched isoprenoid (HBI) alkenes are ubiquitous lipids which have been identified in numerous geochemical samples, ranging from recent sediments to ancient oils. At the outset of the current investigation, the diatomaceous algae Haslea ostrearia (C25 alkenes) and Rhizosolenia setigera (C25 or C30 alkenes) were the only reported biological sources of these compounds. However, there remained a poor correlation between isomers found in diatoms and those commonly reported in sediments and water column particles. In the present study, the structures of fourteen novel C25 HBI trienes, tetraenes and pentaenes, and four C30 HBI pentaenes and hexaenes have been rigorously characterised via gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) spectroscopy following isolation from diatoms. The GC-MS characteristics of the four novel C30 HBIs and eight of the novel C25 HBIs characterised herein show an excellent correlation with those of the HBIs commonly reported in sediments and water column particles. In contrast to the HBIs characterised previously, which all possess a saturated branch point and fixed double bond stereochemistry, the common isomers (C25 and C30) possess an unsaturated branch point and exhibit E/Z isomerism about a trisubstituted double bond. Three diatoms belonging to the Pleurosigma genus have been identified as HBI producers. Of these, the benthic species P. intermedium and the planktonic species Pleurosigma sp. have been found to biosynthesise the common C25 HBI isomers. P. planktonicum has also been identified as a producer of C25 HBIs possessing a novel structural type. The HBI distributions in five distinct strains of R. setigera have been investigated, and these were found to be highly variable. Two strains isolated from the northwest Atlantic were found to produce a single, uncommon C25 HBI pentaene, which has also been reported in H. ostrearia. In contrast, R. setigera isolated from the Arabian Sea was found to produce C30 HBIs only, whilst two strains isolated from southern Brittany were found to co-produce the common C25 and C30 HBI isomers. Four diatom species belonging to the Haslea genus have also been newly identified as producers of C25 HBI alkenes. The HBI distributions in H. salstonica, H. crucigera, H. pseudostrearia and Haslea sp. were examined, and HBI production appears to be widespread within the Haslea genus. All of the HBIs identified in these Haslea spp. were of the structural type previously observed in H. ostrearia, and thus do not correspond to the HBI isomers most commonly reported in sediments and particles. Hydrocarbon extracts isolated from sediments and particulates from the Arabian Sea, Cariaco Trench, Peru upwelling region and the Black Sea were examined by GC-MS, and the HBI isomers in these samples were identified

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