Markus Braun

Analysis of gene expression during parabolic flights reveals distinct early gravity responses in Arabidopsis roots

Plant roots are among most intensively studied biological systems in gravity research. Altered gravity induces asymmetric cell growth leading to root bending. Differential distribution of the phytohormone auxin underlies root responses to gravity, being coordinated by auxin efflux transporters from the PIN family. The objective of this study was to compare early transcriptomic changes in roots of Arabidopsis thaliana wild type, and pin2 and pin3 mutants under parabolic flight conditions and to correlate these changes to auxin distribution. Parabolic flights allow comparison of transient 1-g, hypergravity and microgravity effects in living organisms in parallel. We found common and mutation-related genes differentially expressed in response to transient microgravity phases. Gene ontology analysis of common genes revealed lipid metabolism, response to stress factors and light categories as primarily involved in response to transient microgravity phases, suggesting that fundamental reorganisation of metabolic pathways functions upstream of a further signal mediating hormonal network. Gene expression changes in roots lacking the columella-located PIN3 were stronger than in those deprived of the epidermis and cortex cell-specific PIN2. Moreover, repetitive exposure to microgravity/hypergravity and gravity/hypergravity flight phases induced an up-regulation of auxin responsive genes in wild type and pin2 roots, but not in pin3 roots, suggesting a critical function of PIN3 in mediating auxin fluxes in response to transient microgravity phases. Our study provides important insights towards understanding signal transduction processes in transient microgravity conditions by combining for the first time the parabolic flight platform with the transcriptome analysis of different genetic mutants in the model plant, Arabidopsis.

Rapid adaptation to microgravity in mammalian macrophage cells

Despite the observed severe effects of microgravity on mammalian cells, many astronauts have completed long term stays in space without suffering from severe health problems. This raises questions about the cellular capacity for adaptation to a new gravitational environment. The International Space Station (ISS) experiment TRIPLE LUX A, performed in the BIOLAB laboratory of the ISS COLUMBUS module, allowed for the first time the direct measurement of a cellular function in real time and on orbit. We measured the oxidative burst reaction in mammalian macrophages (NR8383 rat alveolar macrophages) exposed to a centrifuge regime of internal 0 g and 1 g controls and step-wise increase or decrease of the gravitational force in four independent experiments. Surprisingly, we found that these macrophages adapted to microgravity in an ultra-fast manner within seconds, after an immediate inhibitory effect on the oxidative burst reaction. For the first time, we provided direct evidence of cellular sensitivity to gravity, through real-time on orbit measurements and by using an experimental system, in which all factors except gravity were constant. The surprisingly ultra-fast adaptation to microgravity indicates that mammalian macrophages are equipped with a highly efficient adaptation potential to a low gravity environment. This opens new avenues for the exploration of adaptation of mammalian cells to gravitational changes.

Material investigations on the thermal stability of solar salt and potential filler materials for molten salt storage

The thermal and chemical stability of solar salt during isothermal tests is assessed under manifold conditions. Solar salt stored at 560°C under synthetic air stabilizes readily after a few days with both nitrate and nitrite content remaining relatively stable over time. A nitrogen atmosphere enhances degradation due to a continuous reduction of nitrate to nitrite. In an open atmosphere CO2 formation is pronounced owing to the reaction of the molten nitrates with atmospheric CO2. The stability of some filler materials, as potential candidates to be used in thermocline storage concepts, was investigated in long term experiments up to 5.000h. Additional anionic traces in the melt as corrosion products from the filler due to the reaction of instable mineral species with nitrates/nitrites were identified. However, No impact on the the thermal properties of the salt could be determined. These properties remain to be unchanged over a time frame up to 5.000h which is confirmed by relatively stable nitrate/nitrit...

Methods for Gravitational Biology Research

To study the impact of gravity on living systems on the cellular up to the organismic level, a variety of experimental platforms are available for gravitational biology and biomedical research providing either an almost stimulus-free microgravity environment (near weightlessness) of different duration and boundary conditions. The spectrum of real-microgravity research platforms is complemented by devices which are used to either increase the gravity level (centrifuges) or modify the impact of gravity on biological systems (clinostats and random-positioning machines)—the so-called ground-based facilities. Rotating biological samples horizontally or in a two- or three-dimensional mode is often used to randomize the effect of gravity in the attempt to eliminate the gravity effect on sensing mechanisms and gravity-related responses. Sophisticated centrifuges have been designed allowing studies from cells up to humans, either on ground under hypergravity conditions (> 1 g) or in space, where they offer the chance to stepwise increase the acceleration force from 0 g (microgravity) to 1 g or higher and vice versa. In such a way, centrifuges are used to determine threshold values of gravisensitivity and to unravel molecular and cellular mechanisms of gravity sensing and gravity-related responses. By using the whole spectrum of experimental platforms, gravitational biologists gain deep insight into gravity-related biological processes and continuously increase our knowledge of how gravity affects life on Earth.

Gravity Sensing, Graviorientation and Microgravity

Gravity has constantly governed the evolution of life on Earth over the last 3.5 billion years while the magnetic field of the Earth has fluctuated over the eons, temperatures constantly change, and the light intensity undergoes seasonal and daily cycles. All forms of life are permanently exposed to gravity and it can be assumed that almost all organisms have developed sensors and respond in one way or the other to the unidirectional acceleration force. Here we summarize what is currently known about gravity sensing and response mechanisms in microorganisms, lower and higher plants starting from the historical eye-opening experiments from the nineteenth century up to today’s extremely rapidly advancing cellular, molecular and biotechnological research. In addition to high-tech methods, in particular experimentation in the microgravity environment of parabolic flights and in the low Earth orbit as well as in “microgravity simulators” have considerably improved our knowledge of the fascinating sensing and response mechanisms which enable organisms to explore and exploit the environment on, above and below the surface of the Earth and which was fundamental for evolution of life on Earth.

Bioregenerative Life Support Systems in Space Research

For manned long-term missions e.g. to Mars, large amounts of food and oxygen are required to sustain the astronauts during the months- or year-long travel in space but resources are very limited. Water is already routinely recycled on the ISS. In order to solve the problem of limited food and oxygen resources, bioregenerative life support systems are envisioned with closed nutrient and gas loops. Several ecological model systems varying in the degree of complexity have already been investigated on ground and tested on shorter space flights. Photosynthetic organisms such as flagellates or higher plants produce oxygen when light is available. Simultaneously they take up the carbon dioxide exhaled by the astronauts or other consumers. Urea and ammonia can be detoxified by bacteria. Insertion of a component of primary consumers such as ciliates could be used to produce fish for human consumption.

Gravitropism in Higher Plants: Cellular Aspects

Due to their sessile life style, an important ability of plants is to adjust their growth towards or away from environmental stimuli. Plant responses that involve directed movements are called tropisms. Among the best-known tropisms are phototropism, the response to light, and gravitropism, the response to gravity. Gravity is one of the major factors that govern root growth in plants. Since the emergence of land plants, gravitropism allowed plants to adjust root growth to maximize access to water and nutrients, and shoots to explore and exploit space on and above the surface of the Earth. In this chapter we discuss current knowledge and point out open questions like the nature of the gravireceptor, the role of secondary messengers, hormones and the cytoskeleton. We review the history of plant gravitropism research, from early experiments performed by naturalists like Charles Darwin to the utilization of clinostats, centrifuges and experimentation in the almost stimulus-free environment of microgravity provided by drop towers, parabolic flights of aircrafts and rockets, satellites and low earth orbit space stations, which are increasingly contributing to our understanding of plant gravity sensing and orientation.

Gravitropism in Tip-Growing Rhizoids and Protonemata of Characean Algae

Characean green algae provide two well-established model cell types for gravitropic research. Experiments in the almost stimulus-free microgravity environments of parabolic flights, sounding rocket flights and Space Shuttle missions have contributed greatly to the progress that has been made in the understanding of cellular and molecular mechanisms underlying plant gravity sensing and gravity-oriented growth responses. While in higher-plant statocytes the role of actin in gravity sensing is still enigmatic, there is clear evidence that actin is intimately involved in polarized growth, gravity sensing and the positive and negative gravitropic response of characean rhizoids and protonemata. The apical tip-growth organizing structure, the Spitzenkorper, and a steep gradient of cytoplasmic free calcium are crucial components of a feedback mechanism that controls polarized growth. Microgravity experiments provided evidence that actomyosin plays a key role in gravity sensing by coordinating the position of statoliths, and, upon gravistimulation, directs sedimenting statoliths to specific gravisensitive areas of the plasma membrane, where they initiate the short gravitropic signalling pathways. In rhizoids, statolith sedimentation is followed by a local reduction of cytoplasmic free calcium resulting in differential growth of the opposite subapical cell flanks—the downward bending. The negative gravitropic response of protonemata is initiated by statolith sedimentation in the apical dome causing actomyosin-mediated relocation of the calcium gradient and displacement of the center of maximal growth towards the upper flank.

Gravitational Biology I: Gravity Sensing and Graviorientation in Microorganisms and Plants

Chapter 1: Gravity Sensing, Graviorientation and Microgravity -- Chapter 2: Methods for Gravitational Biology Research -- Chapter 3: Gravitaxis in Flagellates and Ciliates -- Chapter 4: Gravitropism in Tip-Growing Rhizoids and Protonemata of Characean Algae -- Chapter 5: Gravitropism in Fungi, Mosses and Ferns -- Chapter 6: Gravitropism in Higher Plants: Cellular Aspects -- Chapter 7: Gravitropism in Higher Plants: Molecular Aspects -- Chapter 8: Bioregenerative Life Support Systems in Space Research.

Outlook: Future Potential of Biotechnology Research in Space

As has been shown in the previous chapters, biotechnology research in space has led to significant scientific breakthroughs and technological developments with great application potential. This is true for protein crystallization: here, significant progress in structure determination of certain molecules could be achieved with the help of improved crystals grown in space thereby supporting drug discovery and design. It is also true for certain aspects of cell biology; here, not only the basic understanding of gravity perception, transduction and response is in the focus of the scientists, but also the application of the results for tissue engineering and cancer research. The perspectives for the exploration era and for health research are discussed in some detail taking also into account that the utilization of the International Space Station ISS is secured until at least 2024.