Mycosporine-like amino acids (MAAs) profile of a rice-field cyanobacterium Anabaena doliolum as influenced by PAR and UVR

The mycosporine-like amino acid (MAA) profile of a rice-field cyanobacterium, Anabaena doliolum, was studied under PAR and PAR + UVR conditions. The high-performance liquid chromatographic analysis of water-soluble compounds reveals the biosynthesis of three MAAs, mycosporine-glycine (lambda (max) = 310 nm), porphyra-334 (lambda (max) = 334 nm) and shinorine (lambda (max) = 334 nm), with retention times of 4.1, 3.5 and 2.3 min, respectively. This is the first report for the occurrence of mycosporine-glycine and porphyra-334 in addition to shinorine in Anabaena strains studied so far. The results indicate that mycosporine-glycine (monosubstituted) acts as a precursor for the biosynthesis of the bisubstituted MAAs shinorine and porphyra-334. Mycosporine-glycine was under constitutive control while porphyra-334 and shinorine were induced by UV-B radiation, indicating the involvement of UV-regulated enzymes in the biotransformation of MAAs. It seems that A. doliolum is able to protect its cell machinery from UVR by synthesizing a complex set of MAAs and thus is able to survive successfully during the summer in its natural brightly lit habitats.     

Comparative study of gamma-ray and high-energy carbon ion irradiation on negative gravitaxis inEuglena gracilisZ

The effects of ⁶⁰Co gamma-ray and 290 MeV/amu carbon ion irradiation on negative gravitaxis was studied in the photosynthetic flagellate Euglena gracilis strain Z in a dose-response dependent manner. Cells were exposed to the doses (0-200 Gy for water). The negative gravitaxis was quantified by the r-value observed in a recently developed biomonitoring system. The present results demonstrate the inhibitory effects of gamma-rays and 290 MeV/amu carbon ions on negative gravitaxis of the Euglena gracilis strain Z. The 290 MeV/amu carbon ions had a greater impact at a low dose (<40 Gy) than the ⁶⁰Co gamma-rays.     

Environmental effects of ozone depletion and its interactions with climate change: progress report, 2004.

The complexity of the linkages between ozone depletion, UV-B radiation and climate change has become more apparent.     

Photomovement and Photobleaching In Two Gyrodinium Species

The phototactic orientation in Gyrodinium dorsum and G. aureolumhas been analyzed. Both species show only positive phototaxiswith an optimum at about 300 W-m^–2. The mechanism of photoorientationdoes not seem to be based on a dichroic orientation of the photoreceptorpigments as in the flagellate Euglena gracilis. Photobleachingexperiments have shown a far higher resistance toward continuousirradiation at even high fluence rates than in other flagellateswhich is in good agreement with the exclusive behavior of positivephototaxis. (Received August 7, 1987; Accepted July 14, 1988)     

Effects of tropical solar radiation on the motility of filamentous cyanobacteria

Abstract The effects of tropical solar radiation on the motility of the cyanobacteria Anabaena variabilis, Oscillatoria tenuis and two strains of Phormidium uncinatum were studied in Ghana (4.30°N). The percentages of motile filaments were drastically reduced by unfiltered solar radiation. Covering the organisms with various long pass or band pass filters (WG320, GG395 or UG5) revealed that the UV-B, UV-A and visible light components of the solar spectrum were all effective in impairing motility in these organisms. Only partial recovery was observed and only after short exposure times.     

Ultraviolet-B inhibition of motility in green and dark bleachedEuglena gracilis

The motility of green and dark bleachedEuglena gracilis was studied under artificial and solar UV-B radiation. The percentage of motile cells in the population was drastically impaired after exposure to unfiltered sunlight for only a few hours. Dark bleached cells were even more affected than green organisms. The effect is caused mainly by the solar UV-B component, since filtering the sunlight by either a layer of ozone or a UV-B-absorbing filter substantially increased the survival rate. Addition ofp-quinone, a scavenger of free radicals produced in a type I photodynamic reaction, did not relieve the UV-B effects, but was cytotoxic at higher concentrations. Likewise, 1,4-diazobicyclo[2,2,2]octane and imidazole, which quench singlet oxygen (¹O₂) generated in a type II photodynamic reaction, did not prolong the survival in UV-B irradiation. D₂O, which, in contrast, prolongs the lifetime of¹O₂, is tolerated by the cells but does not aggravate the UV-B inhibition. Thus, photodynamic processes of both type I and II can be ruled out as possible mechanisms of UV-B inhibition of motility inEuglena gracilis.     

Movement of Dictyostelium Pseudoplasmodia in Vivo and in a Mathematical Simulation

An improved mathematical model simulating the movement of Dictyosteliumdiscoideum slugs on a plane surface is presented and comparedwith the results obtained in vivo. The model allows the simulationof random movements under non-stimulated conditions and theoriented movement in the presence of photic, thermal and chemicalstimuli. The simulation supports the hypothesis that the externalstimuli are internally converted into a gradient of a low molecularweight substance in which the organisms orient chemotactically.A spatially defined field containing this substance is avoidedby the organisms while a uniform background decreases the degreeof orientation to a light stimulus both in vivo and in the simulation.The behavior observed in mutants can be simulated by adjustingthe sensitivity coefficients in the simulation functions forthe various stimuli. (Received December 10, 1983; Accepted April 12, 1984)     

Mathematical Simulation of Dictyostelium Pseudoplasmodia Movements

A mathematical model has been developed to simulate the movement of Dictyostelium discoideum slugs. The model allows simulation of random motility in the absence of external stimuli based on spatial and temporal changes in the microenvironment. In addition the effects of external stimuli such as laterally impinging light and thermal gradients have been simulated. The model allows us to study the effect of simultaneous application of different stimuli. A statistical analysis incorporated in the model allows us to evaluate quantitatively the directedness of movement and the angle of deviation from the stimulus direction as well as the angular distribution of track segments in 5° sectors. The results are discussed in comparison with the experimental data obtained in vivo as well as the ecological effects of multiple stimuli.