Survival of a desiccation-tolerant moss,Grimmia laevigata,beyond its observed microdistributional limits

Abstract

The desiccation-tolerant moss, Grimmia laevigata, dominates the vegetation on exposed granitic boulders at a semi-arid site in southern California but fails to occur in especially xeric microsites, on overhanging surfaces, and on boulders of southfacing hillsides. It was hypothesized that establishment, rather than adult survival, limits the microdistribution of the moss. As predicted, adult plants transplanted to these microsites outside the observed microdistribution of the species showed no evidence of reduced function after one year. However, direct studies of establishment are required to confirm the hypothesis. Differences in net photosynthesis and chlorophyll content among transplants suggested that these characteristics were phentotypically plastic and changed with light availability. In the absence of potential photodamage, G. laevigata can completely conserve chlorophyll during desiccation for at least twenty months.     

The limits of reductionism in the life sciences

In the contemporary life sciences more and more researchers emphasize the "limits of reductionism" (e.g. Ahn et al. 2006a, 709; Mazzocchi 2008, 10) or they call for a move "beyond reductionism" (Gallagher/Appenzeller 1999, 79). However, it is far from clear what exactly they argue for and what the envisioned limits of reductionism are. In this paper I claim that the current discussions about reductionism in the life sciences, which focus on methodological and explanatory issues, leave the concepts of a reductive method and a reductive explanation too unspecified. In order to fill this gap and to clarify what the limits of reductionism are I identify three reductive methods that are crucial in the current practice of the life sciences: decomposition, focusing on internal factors, and studying parts in isolation. Furthermore, I argue that reductive explanations in the life sciences exhibit three characteristics: first, they refer only to factors at a lower level than the phenomenon at issue, second, they focus on internal factors and thus ignore or simplify the environment of a system, and, third, they cite only the parts of a system in isolation.     

Physical limits of computation and emergence of life

The computational process is based on the activity linking mathematical equations to a materialized physical world. It consumes energy which lower limit is defined by the set of Planck's values, i.e. by the physical structure of the Universe. We discuss computability from the quantum measurement framework. Effective quantum computation is possible via the maintenance of a long-living cold decoherence-free internal state, which is achieved by applying error-correction commands to it and by screening it from thermal fluctuations. The quantum Zeno effect enables coherent superpositions and entanglement to persist for macroscopic time intervals. Living systems maintain coherent states via realization of their own computing programs aiming them to survive and develop, while their non-computable behavior corresponds to a generative power that arises beyond combinatorial capabilities of the system. Emergence of life brings in the Universe a creative activity that overcomes the limits of computability.     

Ecophysiological responses of desiccation-tolerant cryptobiotic crusts

In our present studies, the recovery of photosynthetic activity after rehydration was demonstrated. We measured chlorophyll fluorescence, CO₂ gas exchange and the pigment composition in the previously long-term air-dried cryptogamic inselberg crusts collected from two tropical areas. The cryptobiotic crusts were collected from different localities on similar ecological and climatic conditions from extreme habitats of inselbergs (outcrops). These inselbergs are characterized by a dry microclimate and are covered by scarce soil. We found that the ecophysiological responses of both cryptogamic inselberg crusts showed an extremely high degree of desiccation-tolerance due to the fast and full recovery during rehydration. The photosynthetic activity of the cryptobiotic crusts were restored and regained within 15 and 40 min, respectively, after rehydration. Photosynthetic activity of the crusts was retained at all applied light intensities when enough water was available, however the degree of the recovery was different between the crusts. Photosynthetic pigment contents were strongly and positively correlated with water content. Our results indicated that tropical desiccation-tolerant cryptogamic crusts found on inselberg rock surfaces have CO₂ fixation ability in the range of cyanobacteria and lichens, suggesting that at a global scale they can assimilate CO₂ in a significant amount.     

Ecophysiology of Antarctic marine ectotherms: limits to life

The ecophysiology of Antarctic marine ectotherms is an area of active research. This review of recent progress covers metabolism, mitochondrial function, aerobic scope, growth and development. Energetics is shown to be a central feature of adaptation to temperature, with mitochondrial function and tissue oxygen supply important in setting limits to organismal size and performance.     

Agrobacterium-mediated transformation of the desiccation-tolerant plant Craterostigma plantagineum

Summary An efficient procedure for Agrobacterium tumefaciens- mediated transformation of the desiccation-tolerant plant Craterostigma plantagineum has been developed. Leaf explants were inoculated with A. tumefaciens strain GV3101 carrying the gene for kanamycin- or hygromycin-resistance and the ßglucuronidase reporter gene. Parameters which affected the transformation efficiency were the age of the explant, the degree of wounding and the presence of an antioxidant in the medium. Under optimal conditions, calli originated in more than 80% of leaf explants. Transformed plants were obtained from more than 50% of the cultured calli during regeneration in the presence of a suitable antibiotic. The stable integration of T-DNA was confirmed by Southern blot analysis and its expression by assays for ß-glucuronidase activity.Abbreviations GUS ß-glucuronidase - MUG 4-methyl-umbelliferyl ß-D-glucuronide - ABA abscisic acid - NPTII neomycin phosphotransferase II - CaMV cauliflower mosaic virus - MSAR modified MS medium - MS Murashige and Skoog     

The bright frontiers of microbial metabolic optogenetics

In recent years, light-responsive systems from the field of optogenetics have been applied to several areas of metabolic engineering with remarkable success. By taking advantage of light's high tunability, reversibility, and orthogonality to host endogenous processes, optogenetic systems have enabled unprecedented dynamical controls of microbial fermentations for chemical production, metabolic flux analysis, and population compositions in co-cultures. In this article, we share our opinions on the current state of this new field of metabolic optogenetics.We make the case that it will continue to impact metabolic engineering in increasingly new directions, with the potential to challenge existing paradigms for metabolic pathway and strain optimization as well as bioreactor operation.     

Thermodynamic limits to microbial life at high salt concentrations

Life at high salt concentrations is energetically expensive. The upper salt concentration limit at which different dissimilatory processes occur in nature appears to be determined to a large extent by bioenergetic constraints. The main factors that determine whether a certain type of microorganism can make a living at high salt are the amount of energy generated during its dissimilatory metabolism and the mode of osmotic adaptation used. I here review new data, both from field observations and from the characterization of cultures of new types of prokaryotes growing at high salt concentrations, to evaluate to what extent the theories formulated 12 years ago are still valid, need to be refined, or should be refuted on the basis of the novel information collected. Most data agree well with the earlier theories. Some new observations, however, are not easily explained: the properties of Natranaerobius and other haloalkaliphilic thermophilic fermentative anaerobes, growth of the sulfate-reducing Desulfosalsimonas propionicica with complete oxidation of propionate and Desulfovermiculus halophilus with complete oxidation of butyrate, growth of lactate-oxidizing sulfate reducers related to Desulfonatronovibrio at 346 g l(-1) salts at pH 9.8, and occurrence of methane oxidation in the anaerobic layers of Big Soda Lake and Mono Lake.     

Peroxidase activity of desiccation-tolerant loblolly pine somatic embryos

Summary Desiccation tolerance can be induced by culturing somatic embryos of loblolly pine (Pinus taeda L.) on medium supplemented with 50 μM abscisic acid (ABA) and/or 8.5% polyethylene glycol (PEG₆₀₀₀). Scanning electron microscopy of desiccated somatic embryos showed that the size and external morphology of the desiccation-tolerant somatic embryos recovered to the pre-desiccation state within 24–36 h, whereas the non-desiccation-tolerant somatic embryos did not recover and remained shriveled, after rehydration. Peroxidase activity of desiccated somatic embryos increased sharply after 1 d of desiccation treatment at 87% relative humidity (RH), and desiccation-tolerant somatic embryos had higher peroxidase activity compared to sensitive somatic embryos. Higher peroxidase activity of desiccation-tolerant somatic embryos may have allowed them to catalyze the reduction of H₂O₂ produced by drought stress, and protected them from oxidative damage.     

Purification of polysomes from a lysozyme- resistant desiccation-tolerant cyanobacterium

Six different techniques were compared for the extraction and purification of polysomes from cells of the desiccation-tolerant cyanobacterium Nostoc commune UTEX 584. Cells resisted treatment with lysozyme, and methods which relied upon ‘gentle lysis’ resulted in inefficient cell breakage and poor yields of polysomes. In contrast, the passage of cells through a French Pressure Cell achieved complete disruption of even the most resistant cell aggregates but only monosomes and ribosomal subunits were recovered. The grinding of cells with glass beads in the presence of neutral detergents was the most successful of all the methods tested and resulted in efficient cell lysis with high yields of polysomes. Treatment of the cells with acetone, at 0°C, prior to homogenization, also resulted in good yields of polysomes although the degree of cell breakage was less than when the cells were ground. The choice of the grinding material, and the extent of the grinding, were both critical for polysome extraction. Grinding of cells with alumina and sterile sand gave very efficient cell breakage but no polysomes were recovered. Excessive grinding with glass beads led to a progressive loss of intact polysomes and concomitant increase in 70 S monosomes and subunits in cell extracts.This study provides data on various physical treatments and buffer compositions which may be used effectively in the isolation and purification of polysomal RNA from highly resistant bacterial cells. A method which relies upon the grinding of cells in the presence of neutral detergents will permit further studies of gene expression in cells which resist methods of ‘gentle lysis’.     

The limits of subfunctionalization

Background  

The duplication-degeneration-complementation (DDC) model has been proposed as an explanation for the unexpectedly high retention of duplicate genes. The hypothesis proposes that, following gene duplication, the two gene copies degenerate to perform complementary functions that jointly match that of the single ancestral gene, a process also known as subfunctionalization. We distinguish between subfunctionalization at the regulatory level and at the product level (e.g within temporal or spatial expression domains).     

The limits of log-ratios

Background  

DNA microarray assays typically compare two biological samples and present the results of those comparisons gene-by-gene as the logarithm base two of the ratio of the measured expression levels for the two samples.     

专家论藻类学的新前沿

随着可供利用的陆生资源的日益枯竭以及系统生物学与整合生物技术的兴起,藻类学研究正面临着许多前所未有的挑战与机遇。在312次香山科学会议——《藻类学的新前沿》上,与会专家围绕“系统生物学时代的藻类学研究”、“面向资源环境新需求的藻类生物技术”、“藻类学科和藻类产业的可持续发展”、“藻类与环境”等关键问题,进行了深入的探讨。