Effects of the season and growth stage on the contents of lipids and photosynthetic pigments in brown alga <Emphasis Type="Italic">Undaria pinnatifida</Emphasis>

Seasonal changes in the contents of lipids and photosynthetic pigments (PSP) in the brown alga Undaria pinnatifida (Harvey) Suringar (Phaeophyceae, Alariaceae) on different stages of its growth were studied. Lipids of all plant growth group comprised glyceroglycolipids (GL), phospholipids, and neutral lipids (NL). The ratio between these lipid groups and the content of particular lipids depended on the season and algal growth stage: NL predominated in seedlings; juvenile algae comprised approximately similar amounts of NL and GL; and in adult algae, GL predominated. In winter and spring, algal tissues contained relatively more free sterols than in summer. Total lipid content in seedlings and juvenile algae was higher then in adult plants. Lipid fatty acid (FA) composition was similar on all growth stages, but the content of major components differed; this is mainly related to 18:4 n-3, 20:4 n-6, and 20:5 n-3 acids. The predominant FAs in seedling lipids were saturated FAs, whereas in the lipids of juvenile and adult algae, polyunsaturated FAs predominated.     

Alfvén resonance heating in Uragan-2M torsatron

Uragan-2M is a medium-size torsatron with reduced helical ripples. This machine has the major plasma radius R = 1.7 m, the average minor plasma radius r _p ≤ 0.24 m and the toroidal magnetic field B ₀ ≤ 2.4 T. The Alfvén resonance heating in a high k _‖ regime is advantageous for small size machines since it can be realized at smaller plasma densities than the minority and second harmonic heating. The Alfvén resonance heating is examined numerically in the approximation of radially non-uniform plasma cylinder with identical ends. The numerical model for wave excitation and propagation accounts for the longitudinal electron thermal motion and the finite ion gyroradius which allow the model to treat correctly the propagation and damping of the kinetic Alfvén wave in hot plasma. A compact antenna consisting of four loop elements is chosen to provide operation in a high k _‖ regime. The major drawback of such an approach is the presence of plasma peripher y heating owing to unavoidable excitation of low k _‖ Alfvén resonances. Calculations show that, with the proper choice of heating regime, the periphery heating has an acceptable level and the major part of the power is deposited inside plasma column.     

Generation of soft X-ray emission by Z-pinches powered from helical explosive magnetocumulative generators

Results are presented from experiments on the implosion of wire arrays powered from 100-and 200-mm-diameter helical explosive magnetocumulative generators with explosive opening switches. The experiments were performed at load currents of up to 4 MA, the current rise time being 0.3–0.4 μs. The maximum soft X-ray yield of ～ 100 kJ was achieved at a pinch plasma temperature of 55 eV. A two-dimensional MHD code was developed to simulate the process of liner implosion and the generation of X-ray emission. The results of computer simulations agree satisfactorily with the experimental data.     

Chinese hamster cells mutant at the hypoxanthine-guanine phosphoribosyltransferase (GPRT) locus. V. Complementation analysis of ts mutants

Four temperature-sensitive HPRT clones were used for hybridological analysis, which led to increase in complementation rate about 5 times. The probability of complementation, in respect of the HPRT locus proved to be rather high: 14 of 45 hybridization-tested mutants had complementation ability (including 3 ts mutants). Analysis of the complementation rate among mutants revealed clear-cut dependence on the selection conditions: clones grown in a medium with 8-azaguanine showed most frequent complementation. The use of mutants with a new phenotype in hybridization analysis revealed four additional complementation groups, three of which are made of temperature-sensitive clones. Biochemical analysis revealed the presence of hybrid forms of the HPRT enzyme in all hybrids tested. This confirms the intragenic character of complementation. At present, the functional map of the HPRT locus is represented by 9 groups, including a group of mutants with no complementation ability.     

Seasonal changes in the content of lipids,fatty acids,and pigments in brown alga <Emphasis Type="Italic">Costaria costata</Emphasis>

We compared the content of total lipids, particular lipid classes, fatty acids (FAs), and pigments in the brown alga Costaria costata [Turn.] Saund (Laminariaceae) in different seasons: during algal active life (April–June) and in the beginning of their degradation (the end of July). Lipids comprised only a small part of algal extractable compounds (10.9–13.4%). Their higher content was observed in May, in the period of alga preparation to sporogenesis. Polar lipids, glyceroglycolipids (GL) and phospholipids (PL), comprised a great part of total lipids in spring months and June, whereas neutral lipids, in July. GL predominated in polar lipids in spring and summer. The highest content of GL was observed in May and PL in April. Storage lipids comprised a great part of lipids in July. The content of sterols was the highest in April and May. In summer months, the content of sterols decreased and remained on unchanged level until thallus degradation. Polyunsaturated FAs (PUFAs) comprised the most part of FAs. Their highest content was observed in April. The main part of PUFAs were those of ω-3 series. In July, the level of these PUFA decreased substantially. The levels of ω-6 PUFAs were approximately similar in spring and summer months. The lowest content of monounsaturated FAs was detected in April; in May and July; the relative content of these FAs increased sharply. We also detected seasonal changes in the content of pigments and the ratios between them.     

Versatility of the green microalga cell vacuole function as revealed by analytical transmission electron microscopy

Vacuole is a multifunctional compartment central to a large number of functions (storage, catabolism, maintenance of the cell homeostasis) in oxygenic phototrophs including microalgae. Still, microalgal cell vacuole is much less studied than that of higher plants although knowledge of the vacuolar structure and function is essential for understanding physiology of nutrition and stress tolerance of microalgae. Here, we combined the advanced analytical and conventional transmission electron microscopy methods to obtain semi-quantitative, spatially resolved at the subcellular level information on elemental composition of the cell vacuoles in several free-living and symbiotic chlorophytes. We obtained a detailed record of the changes in cell and vacuolar ultrastructure in response to environmental stimuli under diverse conditions. We suggested that the vacuolar inclusions could be divided into responsible for storage of phosphorus (mainly in form of polyphosphate) and those accommodating non-protein nitrogen (presumably polyamine) reserves, respectively.The ultrastructural findings, together with the data on elemental composition of different cell compartments, allowed us to speculate on the role of the vacuolar membrane in the biosynthesis and sequestration of polyphosphate. We also describe the ultrastructural evidence of possible involvement of the tonoplast in the membrane lipid turnover and exchange of energy and metabolites between chloroplasts and mitochondria. These processes might play a significant role in acclimation in different stresses including nitrogen starvation and extremely high level of CO₂ and might also be of importance for microalgal biotechnology. Advantages and limitations of application of analytical electron microscopy to biosamples such as microalgal cells are discussed.     

Monte Carlo simulations and measurement of DNA damage from x-ray-triggered Auger cascades in iododeoxyuridine (IUdR)

We investigated the DNA damage from Auger electrons emitted from incorporated stable iodine (¹²⁷I), following photoelectric absorption of external x-rays. The effectiveness of the Auger electrons in producing DNA double-strand breaks (DSB) was determined theoretically, using Monte Carlo simulations of the radiation physics and chemistry, and was shown to be in reasonable agreement with DNA damage measured using the comet assay. The DSB yields were measured in CHO cells for ⁶⁰Co (as a non-Auger-promoting radiation) and for tungsten-filtered 100 kVp x-rays capable of producing Auger electron emission. The theoretical study showed that on average, 2.5 Auger electrons were emitted for N-shell orbital vacancies and up to 10 Auger electrons were emitted from L₁-shell vacancies. These Auger bursts produced approximately 0.03 DSB per N-shell vacancy and 0.3 DSB per K-shell or L-shell vacancy. The calculated yield of DSB from Auger cascades per unit dose (1 Gy) in water was approximately 1.7 for tungsten-filtered 100 kVp x-rays, assuming 20% IUdR substitution of thymidine. The comet assay yielded an experimental value of 3.6±1.6 per 1 Gy for the same conditions. The Monte Carlo simulations also demonstrated a high complexity of DSB produced by Auger cascades with virtually all DSB from inner shell orbitals (i.e. K, L shells) accompanied by compounded strand breakage and base damage, indicating a difficult lesion to repair. This finding agrees well with comet assay results of DNA repair, where an increase in the DSB yield in IUdR-sensitized cells was shown to persist after a time of 24 h. We conclude that Auger cascades in iodine produce a modest increase in the number of initial strand breaks of the order of 10% but the complex nature of these DSB makes them very difficult to repair or potentially prone to misrepair. The accentuated DNA damage may have major consequences for cell survival and may be exploitable in kilovoltage photon activation therapy (PAT) of tumors sensitized with iodine. Received: 23 October 2000 / Accepted: 26 March 2001