The Effect of Decreasing the External Salinity on the Primary Processes of Photosynthesis in Dunaliella tertiolecta

The euryhaline unicellular green alga Dunaliella tertiolectalost intracellular glycerol when subjected to a decrease inexternal salinity. After the salinity was decreased, photosynthesiswas inhibited for at least the first 100 min, but dark oxygenuptake was transiently stimulated. The extent of the 519 nmfield-indicating absorption change induced by photosystem Ialone was inhibited by decreasing the salinity, but other photosyntheticparameters were largely unaffected. A comparison of these resultswith hypertonic stress indicated that although both stressesinhibit the overall process of photosynthesis, they do so bydifferent mechanisms. Resuspending the algal cells in distilledwater resulted in an inhibition of all the photosynthetic parametersmeasured. Key words: Dunaliella, Photosynthesis, Hypotonicity     

The Effect of Osmotic and Ionic Stress on the Primary Processes of Photosynthesis in Dunaliella tertiolecta

Cells of the euryhaline unicellular green alga Dunaliella tertiolectawere exposed to a range of osmotic potentials imposed by theaddition of NaCl, KCl, sucrose or ethylene glycol to the algalsuspending medium. The alga synthesized glycerol in responseto increased concentrations of NaCl, KCl or sucrose, but notto increased concentrations of ethylene glycol. The overallprocess of photosynthesis was inhibited by all four treatmentsduring the first 100 min, but especially by NaCl and KCl. Theinduction of chlorophyll fluorescence indicated that photosystemIl was inhibited by such treatment although to a lesser extentthan the overall process. The size and half-time of decay ofthe flash-induced field-indicating absorption change at 519nm were decreased by NaCl and KCl but the effect of sucroseand ethylene glycol on the absorption change was much less.Therefore, the photosynthetic processes in intact Dunaliellacells are more markedly inhibited by the combined osmotic andionic stresses due to NaCl and KCl than by osmotic stress alone.In most cases some recovery of the inhibition of photosynthesiswas seen concomitant with the synthesis of intracellular glycerol,suggesting that the alga has the ability to overcome osmoticand ionic stresses. Key words: Dunaliella, Photosynthesis, Osmotic stress     

Characterization of microsatellite loci in silver carp (Hypophthalmichthys molitrix), and cross‐amplification in other cyprinid species

Captive populations of silver carp (Hypophthalmichthys molitrix), a major aquaculture species in Asia, would undoubtedly benefit from genetic monitoring and improvement programs. We report the isolation and preliminary characterization of 16 microsatellite loci derived from both conventional and microsatellite‐enriched libraries. Inheritance studies confirmed the allelic nature of observed polymorphisms at all loci, while identifying null alleles at two loci. These loci, having varying degrees of polymorphism, should provide useful markers for applied genetic studies. A high degree of cross‐amplification among 10 other cyprinid species suggests that these loci may have more widespread utility.     

X-Ray Microanalysis and Ultrastructural Studies of Cell Compartments of Dunaliella parva

Hajibagheri, M. A., Gilmour, D. J., Collins, J. C. and Flowers,T. J. 1986. X-ray microanalysis and ultrastructural studiesof cell compartments of Dunaliella parva. -J. exp. Bot. 37:1725–1732. Ultrastructural studies of the unicellular green alga Dunaliellaparva showed the presence of cytoplasmic vacuoles. X-ray microanalysiswas performed on sections of cells which had been freeze substitutedin acetone. It was found that the concentrations of both Naand Cl were much higher in the vacuoles than in the cytoplasm.When cells were grown in 0·4 kmol m^–3 NaCl theNa and Cl concentrations in the vacuoles were 349 and 283 molm ^–3 respectively, whilst cytoplasmic Na and Cl concentrationswere 37 and 26 mol m^–3. Corresponding values for cellsgrown in 1·5 kmol m^–3 NaCl were 392 mol m^–3Na and 325 mol m^–3 Cl in the vacuoles and 36 mol m^–3Na and 30 mol m^–3 Cl in the cytoplasm. Immediately afterexposure to an increase in external salinity Na and Q concentrationsincreased in both vacuoles and cytoplasm. The results are discussedwith reference to compartmental models for the ionic relationsof Dunaiiella. Key words: X-ray microanalysis, ultrastructural studies, Dunaliella parva     

The microbe–mineral environment and gypsum neogenesis in a weathered polar evaporite

Evaporitic deposits are a globally widespread habitat for micro‐organisms. The microbe–mineral environment in weathered and remobilized gypsum from exposed mid‐Ordovician marine evaporite beds in the polar desert of Devon Island, Nunavut, Canadian High Arctic was examined. The gypsum is characterized by internal green zones of cyanobacterial colonization (dominated by Gloeocapsa/Aphanothece and Chroococcidiopsis spp. morphotypes) and abundant black zones, visible from the surface, that contain pigmented cyanobacteria and fungi. Bioessential elements in the gypsum are primarily provided by allochthonous material from the present‐day polar desert. The disruption, uplift and rotation of the evaporite beds by the Haughton meteorite impact 39 Ma have facilitated gypsum weathering and its accessibility as a habitat. No cultured cyanobacteria, bacteria and fungi were halophilic consistent with the expectation that halophily is not required to persist in gypsum habitats. Heterotrophic bacteria from the evaporite were slightly or moderately halotolerant, as were heterotrophs isolated from soil near the gypsum outcrop showing that halotolerance is common in arctic bacteria in this location. Psychrotolerant Arthrobacter species were isolated. No psychrophilic organisms were isolated. Two Arthrobacter isolates from the evaporite were used to mediate gypsum neogenesis in the laboratory, demonstrating a potential role for microbial biomineralization processes in polar environments.