The photolytic degradation and oxidation of organic compounds under simulated Martian conditions

Summary Cosmochemical considerations suggest various potential sources for the accumulation of organic matter on Mars. However the Viking Molecular Analysis did not indicate any indigenous organic compounds on the surface of Mars. Their disappearance from the top layer is most likely caused by the combined action of the high solar radiation flux and various oxidizing species in the Martian atmosphere and regolith. In this study the stability of several organic substances and a sample of the Murchison meteorite was tested under simulated Martian conditions. After adsorption on powdered quartz, samples of adenine, glycine and naphthalene were irradiated with UV light at various oxygen concentrations and exposure times. In the absence of oxygen, adenine and glycine appeared stable over the given irradiation period, whereas a definite loss was observed in the case of naphthalene, as well as in the volatilizable and pyrozable content of the Murchison meteorite. The presence of oxygen during UV exposure caused a significant increase in the degradation rate of all samples. It is likely that similar processes have led to the destruction of organic materials on the surface of Mars.     

Regulation of root water uptake under abiotic stress conditions

A common effect of several abiotic stresses is to cause tissue dehydration. Such dehydration is caused by the imbalance between root water uptake and leaf transpiration. Under some specific stress conditions, regulation of root water uptake is more crucial to overcome stress injury than regulation of leaf transpiration. This review first describes present knowledge about how water is taken up by roots and then discusses how specific stress situations such as drought, salinity, low temperature, and flooding modify root water uptake. The rate of root water uptake of a given plant is the result of its root hydraulic characteristics, which are ultimately regulated by aquaporin activity and, to some extent, by suberin deposition. Present knowledge about the effects of different stresses on these features is also summarized. Finally, current findings regarding how molecular signals such as the plant hormones abscisic acid, ethylene, and salicylic acid, and how reactive oxygen species may modulate the final response of root water uptake under stress conditions are discussed.     

Automorphogenesis of maize roots under simulated microgravity conditions

Plant seedlings show exaggerated growth responses on a three-dimensional clinostat. Such an automorphogenesis appears to be one of major factors which govern the life cycle of higher plants under a microgravity environment. On the three-dimensional clinostat, maize roots exhibited curvatures in three different portions; 1) the basal region just protruding from the coleorhiza, 2) the region between the mature and the elongation zone, and 3) the elongation zone, several mm from the tip. Even non-clinostatted control roots showed some degree of curvature. The curvature occurred at random without any dorsiventrality. There was no difference in the osmotic concentration of the cell sap between the convex and the concave halves of any region. However, the convex, rapidly expanding side exhibited a higher extensibility of the cell wall in some regions, which appears to be a cause of the curvature. In order to understand the role of gravity in regulation of plant growth and development, we should clarify a series of events by which an automorphogenesis is induced under simulated microgravity conditions.     

耕作对土壤入渗性能的影响

耕作影响降雨入渗、径流、土壤侵蚀过程。研究采用新型的坡地降雨条件下土壤入渗能力的径流-入渗-产流测量方法和仪器,野外观测宁夏南部山区坡耕地与撂荒地土壤入渗性能,揭示耕作对土壤入渗性能影响的规律。在坡度为20°、土壤表层含水量11.3%的坡地进行测量。采用的降雨强度为:20,40,56mm·h-1。结果表明,新型测量方法和仪器可以很好地测量坡面土壤入渗性能的全过程,并且具有省水、省工、操作方便的特点,且测量精度高。对比测量结果表明,坡耕地的初期土壤入渗性能在小雨强条件下略高于撂荒地的入渗性能,而在大雨强条件下则一直低于撂荒地的入渗性能。随雨强的增大坡耕地的入渗性能急剧减小,而撂荒地的入渗性能基本不受雨强变化的影响。坡耕地土壤的入渗性能(土壤结构)对降雨强度极为敏感,而撂荒地具有稳定的土壤结构和入渗性能。在3种雨强下,坡耕地的产流时间均比撂荒地提前。与撂荒地相比,各种雨强条件下坡耕地的稳定入渗率都较撂荒地明显降低。     

Metabolism of reactive nitrogen species in pea plants under abiotic stress conditions

Nitric oxide (*NO) is a key signaling molecule in different physiological processes of animals and plants. However, little is known about the metabolism of endogenous *NO and other reactive nitrogen species (RNS) in plants under abiotic stress conditions. Using pea plants exposed to six different abiotic stress conditions (high light intensity, low and high temperature, continuous light, continuous dark and mechanical wounding), several key components of the metabolism of RNS including the content of *NO, S-nitrosothiols (RSNOs) and nitrite plus nitrate, the enzyme activities of l-arginine-dependent nitric oxide synthase (NOS) and S-nitrosogluthathione reductase (GSNOR), and the profile of protein tyrosine nitration (NO(2)-Tyr) were analyzed in leaves. Low temperature was the stress that produced the highest increase of NOS and GSNOR activities, and this was accompanied by an increase in the content of total *NO and S-nitrosothiols, and an intensification of the immunoreactivity with an antibody against NO(2)-Tyr. Mechanical wounding, high temperature and light also had a clear activating effect on the different indicators of RNS metabolism in pea plants. However, the total content of nitrite and nitrate in leaves was not affected by any of these stresses. Considering that protein tyrosine nitration is a potential marker of nitrosative stress, the results obtained suggest that low and high temperature, continuous light and high light intensity are abiotic stress conditions that can induce nitrosative stress in pea plants.     

Performance of Chlorella sorokiniana under simulated extreme winter conditions

High annual microalgae productivities can only be achieved if solar light is efficiently used through the different seasons. During winter the productivity is low because of the light and temperature conditions. The productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed under the worst-case scenario found during winter time in Huelva, south of Spain. The maximum light intensity (800?μmol photons m^-2 s^-1) and temperature (20°C) during winter were simulated in a lab-scale photobioreactor with a short light-path of 14?mm. Chemostat conditions were applied and the results were compared with a temperature-controlled situation at 38°C (optimal growth temperature for C. sorokiniana). When temperature was optimal the highest productivity was found at a dilution rate of 0.18 h^-1 (P _v?=?0.28?g Kg^-1 h^-1), and the biomass yield on light energy was high (Y _x,E?=?1.2?g?mol^-1 photons supplied). However, at suboptimal temperature, the specific growth rate of C. sorokiniana was surprisingly low, not being able to support continuous operation at a dilution rate higher than 0.02 h^-1. The slow metabolism under suboptimal temperature resulted in a decline of the light energy requirements of the cells. Consequently, the maximum winter irradiance was experienced as excessive, leading to a low photosynthetic efficiency and productivity (Y _x,E?=?0.5?g mol^-1 photons supplied, P _v?=?0.1?g Kg^-1 h^-1). At suboptimal temperature a higher carotenoid-to-chlorophyll ratio was observed indicating the activation of light-dissipating processes. We conclude that temperature control and/or light dilution during winter time will enhance the productivity.     

Comparative evaluation of two olive fruit fly parasitoids under varying abiotic conditions

Psyttalia lounsburyi (Silvestri) and P. humilis (Silvestri) (Hymenoptera: Braconidae) were evaluated in California for their potential to control the invasive olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae). Psyttalia lounsburyi is a specialist on B. oleae while P. humilis also attacks other tephritid species. Field cage trials, conducted from 2006 to 2009, were used to compare P. lounsburyi and two populations of P. humilis (Kenya and Namibia) in California’s interior valley and coastal regions. Both parasitoid species reproduced on B. oleae in all trials. Under similar abiotic conditions, offspring production per female was higher in P. humilis than in P. lounsburyi, suggesting that host specificity by P. lounsburyi does not confer a higher efficiency on B. oleae in cultivated olives. Two abiotic factors were shown to impact parasitoid efficiency. First, adult parasitoid survival was poor during periods of high summer temperatures, common to the olive production areas in California’s interior valleys. Second, parasitism levels were lower on B. oleae larvae feeding in larger Ascolano cv. fruit than in smaller Manzanillo cv. fruit. Results are discussed relative to biological control of B. oleae in commercial olives and the usefulness of natural enemies specialized to attack fruit flies in wild olives compared with the larger cultivated olive fruit.     

Construction of protocellular structures under simulated primitive earth conditions

We have developed experimental approaches for the construction of protocellular structures under simulated primitive earth conditions and studied their formation and characteristics. Three types of envelopes; protein envelopes, lipid envelopes, and lipid-protein envelopes are considered as candidates for protocellular structures. Simple protein envelopes and lipid envelopes are presumed to have originated at an early stage of chemical evolution, interaction mutually and then evolved into more complex envelopes composed of both lipids and proteins.Three kinds of protein envelopes were constructedin situ from amino acids under simulated primitive earth conditions such as a fresh water tide pool, a warm sea, and a submarine hydrothermal vent. One protein envelope was formed from a mixture of amino acid amides at 80 °C using multiple hydration-dehydration cycles. Marigranules, protein envelope structures, were produced from mixtures of glycine and acidic, basic and aromatic amino acids at 105 °C in a modified sea medium enriched with essential transition elements. Thermostable microspheres were also formed from a mixture of glycine, alanine, valine, and aspartic acid at 250 °C and above. The microspheres did not form at lower temperatures and consist of silicates and peptide-like polymers containing imide bonds and amino acid residues enriched in valine. Amphiphilic proteins with molecular weights of 2000 were necessary for the formation of the protein envelopes.Stable lipid envelopes were formed from different dialkyl phospholipids and fatty acids.Large, stable, lipid-protein envelopes were formed from egg lecithin and the solubilized marigranules. Polycations such as polylysine and polyhistidine, or basic proteins such as lysozyme and cytochromec also stabilized lipid-protein envelopes.     

Biomechanics of the venous wall under simulated arterial conditions

The failure of vein graft conduits implanted in the arterial circulation has been hypothesized to occur in part due to the exposure of the graft to altered biomechanical and fluid shearing forces. In the present study, these forces are characterized for canine internal jugular veins (IJV) exposed to realistic arterial flow dynamics. Freshly excised vein segments were mounted into a pulsatile perfusion apparatus and exposed to arterial flow conditions (P = 115/75 mmHg and Q = 110 ml min-1) for 2 h. Dynamic measurements of intraluminal pressure and flow rate and vessel wall radial distension were acquired to accurately quantitate the incremental modulus of elasticity; hoop, axial and radial wall stresses; and fluid shearing forces within the vessel. Identical measurements were performed on canine carotid arteries (CCA) to serve as a comparison. Under arterial conditions, IJV segments demonstrated a significant elevation (p less than 0.05) over the CCA in the incremental elasticity modulus, along with a corresponding elevation in hoop and axial wall stresses. Additionally the average wall shearing rate to which the IJV endothelial surface was exposed was a factor of six less than that observed in the CCA. These results are discussed in relationship to the clinical situation of vein graft adaptation to arterial hemodynamics.     

模拟油藏条件下内源微生物群落空间分布规律

【背景】油藏内源微生物群落是开展内源微生物驱油技术的物质基础,由于油藏多孔介质取样技术难度大、成本高,实施内源微生物驱油后从注入端到产出端多孔介质中的内源微生物空间分布规律尚不明确。【目的】通过室内长岩心连续驱替实验模拟油藏内源微生物驱油过程,分析实施后不同空间位点油砂上吸附的内源微生物群落结构,揭示从注入端到产出端内源微生物群落的空间分布规律。【方法】借助高通量测序技术及荧光定量PCR技术解析不同空间位点油砂原位微生物群落信息。【结果】注入端到产出端不同空间位点生态环境的差异及菌属间的相互作用造成油藏内源微生物群落空间分布差异,存在明显的好氧、厌氧空间演替变化规律。岩心前端主要存在一些好氧类的产生物表面活性剂类微生物如假单胞菌属,岩心中部主要存在兼性和厌氧类的微生物如地芽孢杆菌、厌氧杆菌属,岩心末端主要分布严格厌氧类细菌和产甲烷古菌,厌氧类微生物代谢产生的H2、CO2和乙酸分子可以为产甲烷古菌提供代谢底物。【结论】通过室内物模油砂研究,首次明确了内源微生物群落在多孔介质中从注入端到产出端的空间分布规律,证实油藏内源微生物的好氧、厌氧空间接替分布规律,深化了对油藏内源微生物的认识。     

Encapsulation of macromolecules by lipid vesicles under simulated prebiotic conditions

Summary Phospholipid vesicles (liposomes) were subjected to dehydration-hydration cycles in the presence of 6-carboxyfluorescein or salmon sperm DNA. We found that the vesicles fused into multilamellar structures during dehydration with solutes trapped between the lamellae. Upon rehydration the lamellae swelled and formed large vesicular structures containing solute. This model can be used to study encapsulation of macromolecules by lipid membranes to form protocellular structures under prebiotic conditions.     

Impairment of antigen-specific cellular immune responses under simulated microgravity conditions

Summary Microgravity has been implicated to play a role in the observed immune dysfunction of astronauts and cosmonauts after either short-term or long-term space travel. These reports, together with studies describing increased levels of microorganisms in the space cabin environment suggest potential risk for in-flight incidences of infectious diseases. In order to understand the mechanism underlying these immune defects, it is important to have a ground-based model that would reliably mimic the effects of microgravity on antigen-specific immune function. We tested the utility of the rotating wall vessel (RWV) technology developed at NASA as a model system because in the RWV the culture medium and the cells rotate synchronously with the vessel, thereby creating simulated microgravity conditions. We compared the RWV to the conventional tissue culture flask (T-flask), for culturing immune precursor cells with cytotoxic T lymphocyte (CTL) activity against synthetic viral peptides. We observed a significant loss of antigen-specific CTL activity in RWV cultures, but not in those from the T-flask, irrespective of the peptide immunogen used for inducing the primary immune response in different mouse strains. Loss of CTL activity in RWV cultures coincided with a significant reduction in CD8⁺ cells as well as CD4⁺ cells and DEC205⁺ dendritic cells, suggesting adverse effects of RWV culturing on both the effector and accessory cells for the loss of antigen-specific CTL function. These results provide a strong parallel to the reported defects in cell-mediated immunity during space travel and strongly support the utility of the RWV technology as an effective ground-based model for identifying key steps in immune cell dysfunction related to microgravity.     

Psychophysiological monitoring under conditions of real and simulated microgravity.

Dynamics of indices characterizing the process of adaptation of operators to complicated conditions of vital activity was studied with psychophysiological monitoring. This technique is based on the complex analysis of subjective and objective estimations of the current psychoemotional state and physiological and biochemical indices. We analyzed the data obtained during the examination of three healthy volunteers, who participated in the HUBES experiment (135-day isolation in the ground-based model of the orbital station "Mir"), and during a biorhythmological study conducted by six Russian cosmonauts of the main expeditions on the station "Mir." It was shown that psychophysiological monitoring is an informative method for studying different parameters of the operator's state and regulatory processes, the dynamics of biological rhythms, and individual characteristics of adaptation. By means of the analysis of a population of the variation in the characteristics of the parameters under study the experimental period of isolation was divided into three stages. The first and third stages were characterized by a relatively high variability, which was minimized at the second stage. The phasic character of the adaptation processes with a phase duration of about 60 days was revealed and a correlation was shown between the dynamics of parameters obtained by means of psychophysiological monitoring and specific features of the system regulation in different phases of the space flight and its simulation. It is suggested that the phases of the minimal variability of the studied characteristics are related to the periods of the minimal reliability of an operator's work. [Translated from Fiziologiya Cheloveka, vol. 25, no. 5, 1999 Sep-Oct, p. 86-91]     

Thermophilic biotransformations of 2,4,6-trinitrotoluene under simulated composting conditions.

The biotransformations of 14C-labeled 2,4,6-trinitrotoluene by thermophilic microorganisms in a compost system were determined. The reduction products identified in solvent extracts were similar to those identified in mesophilic systems. A significant percentage of the 14C-labeled products were bound to humus fractions.