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PubMed2000

Interactions between photosynthesis and 'light-enhanced dark respiration' (LEDR) in the flagellate Euglena gracilis after irradiation with ultraviolet radiation.

The effects of ultraviolet radiation (UV-A, 315-400 nm plus UV-B, 280-315 nm) on photosynthesis and 'light-enhanced dark respiration' (LEDR) in Euglena gracilis have been investigated by using light pulses (80 s) with increasing photon fluence rates of 59, 163, 600, 1180, 2080 and 3340 micromol m(-2) s(-1) and dark periods between the light pulses. LEDR is estimated as the maximum rate of oxygen consumption after a period of light minus the rate of oxygen consumption 30 s after the maximum rate. Without any exposure to UV radiation, the photosynthetic rate and LEDR increase with increasing photon fluence rate. After 20 and 40 min exposures to UV radiation, the photosynthetic rate and LEDR as functions of photon fluence rate are reduced. After a 20 min UV treatment respiration is greater than photosynthesis after the first light pulse of 59 micromol m(-2) s(-1) radiation, and especially at higher photon fluence rates photosynthesis is lower than the control values. The inhibitory effects of UV radiation on photosynthetic rate and LEDR are greater after a 40 min UV exposure than after a 20 min exposure. Only at 600 micromol m(-2) s(-1) is the rate of oxygen evolution greater than that of oxygen consumption after a 40 min UV treatment. Both photosynthetic rate and LEDR are inhibited by the photosynthetic inhibitor DCMU (10(-5) M) in a similar way, which indicates close regulatory interactions between photosynthesis and LEDR. Potassium cyanide (KCN) inhibits dark respiration more than it inhibits LEDR. Dark respiration is not affected to the same degree by UV radiation as are photosynthesis and LEDR.

Animals↗
PubMed1999

Symbiomonas scintillans gen. et sp. nov. and Picophagus flagellatus gen. et sp. nov. (Heterokonta): two new heterotrophic flagellates of picoplanktonic size.

Two new oceanic free-living heterotrophic Heterokonta species with picoplanktonic size (< 2 microm) are described. Symbiomonas scintillans Guillou et Chrétiennot-Dinet gen. et sp. nov. was isolated from samples collected both in the equatorial Pacific Ocean and the Mediterranean Sea. This new species possesses ultrastructural features of the bicosoecids, such as the absence of a helix in the flagellar transitional region (found in Cafeteria roenbergensis and in a few bicosoecids), and a flagellar root system very similar to that of C. roenbergensis, Acronema sippewissettensis, and Bicosoeca maris. This new species is characterized by a single flagellum with mastigonemes, the presence of endosymbiotic bacteria located close to the nucleus, the absence of a lorica and a R3 root composed of a 6+3+x microtubular structure. Phylogenetical analyses of nuclear-encoded SSU rDNA gene sequences indicate that this species is close to the bicosoecids C. roenbergensis and Siluania monomastiga. Picophagus flagellatus Guillou et Chrétiennot-Dinet gen. et sp. nov. was collected in the equatorial Pacific Ocean. Cells are naked and possess two flagella. This species is characterized by the lack of a transitional helix and lateral filaments on the flagellar tubular hairs, the absence of siliceous scales, two unequal flagella, R1 + R3 roots, and the absence of a rhizoplast. SSU rDNA analyses place this strain at the base of the Chrysophyceae/Synurophyceae lineages.

Animals↗