Space experiment on behaviors of treefrog.

Japanese treefrogs (Hyla japonica) are planned to be sent to the space station MIR. Experimental system was developed to observe their behaviors under microgravity.     

Automorphogenesis and gravitropism of plant seedlings grown under microgravity conditions.

Plant seedlings exhibit automorphogenesis on clinostats. The occurrence of automorphogenesis was confirmed under microgravity in Space Shuttle STS-95 flight. Rice coleoptiles showed an inclination toward the caryopsis in the basal region and a spontaneous curvature in the same adaxial direction in the elongating region both on a three-dimensional (3-D) clinostat and in space. Both rice roots and Arabidopsis hypocotyls also showed a similar morphology in space and on the 3-D clinostat. In rice coleoptiles, the mechanisms inducing such an automorphic curvature were studied. The faster-expanding convex side of rice coleoptiles showed a higher extensibility of the cell wall than the opposite side. Also, in the convex side, the cell wall thickness was smaller, the turnover of the matrix polysaccharides was more active, and the microtubules oriented more transversely than the concave side, and these differences appear to be causes of the curvature. When rice coleoptiles grown on the 3-D clinostat were placed horizontally, the gravitropic curvature was delayed as compared with control coleoptiles. In clinostatted coleoptiles, the corresponding suppression of the amyloplast development was also observed. Similar results were obtained in Arabidopsis hypocotyls. Thus, the induction of automorphogenesis and a concomitant decrease in graviresponsiveness occurred in plant shoots grown under microgravity conditions.     

Modeling of “gradual” solar energeticparticle events using a stochastic differential equation method

We have modeled “gradual” solar energetic particle events through numerical simulations using a StochasticDifferential Equation (SDE) method. We consider that energetic particle events are roughly divided into two groups: (1) where the shock was driven by coronal mass ejections (CMEs) associated with large solar flares, and (2) where they have no related solar events apart from the CMEs. (The detailed classification of energetic particle events was discussed in our previous paper.) What we call “gradual” solar energetic particle events belong to the former group. Particles with energies greater than 10 MeV are observed within several hours after the occurrence of flares and CMEs in many gradual events. By applying the SDE method coupled with particle splitting to diffusive acceleration, we found that an injection of high energy particles is necessary for early enhancement of such a high-energy proton flux and that it should not be presumed that the solar wind particles act as the seed population.     

Ground Compatibility Tests for Gravity Measurement of SELENE: Accuracies of Two- and Four-Way Doppler and Range Measurements

The Japanese lunar mission Selenological and Engineering Explorer (SELENE) was launched in September 2007 and continued its mission until June 2009, when the main orbiter impacted with the surface of the Moon. SELENE consisted of three satellites: Main, Rstar, and Vstar. Rstar’s tasks were to forward up-link signals from the Usuada Deep Space Center (UDSC) to Main, and to down-link returning signals from Main to UDSC. We refer to this tracking sub-system as a four-way Doppler measurement. In contrast, conventional tracking systems between Rstar and UDSC as well as between Main and ground stations are referred to as two-way Doppler and range measurements. Using Main and Rstar, we successfully observed the gravity field over the farside of the Moon. Because four-way Doppler measurements via a relay sub-satellite were a fundamental experiment in space for Japanese space agencies, compatibility of radiometric instruments onboard Main and Rstar to UDSC were carefully examined at the UDSC using components manufactured for flight models. These tests not only proved the feasibility of the four-way Doppler measurements but also provided biases and variations of the four-way Doppler and two-way Doppler and range measurements that were later taken into account during the processing of tracking data and the analysis of the lunar global gravity field.     

Emesis and space motion sickness in amphibians.

Amphibians possess the ability to vomit in response to a variety of stimuli that provoke emesis in mammals. Pharmacological studies have establish that the ejection of gastric contents and the basic mechanism for vomiting have been phylogenetically conserved among these tetrapods. As part of on-going comparative studies on emesis in vertebrates, we previously documented that some postmetamorphic anurans and salamander larvae experience motion-induced emesis when exposed to the provocative stimulus of parabolic aircraft flight. However, more recent experiments suggest that there are strict conditions for inducing emesis in amphibians exposed to parabolic flight and that amphibians are not as sensitive to this stimulus as mammals. Further studies on emesis in lower vertebrates may help us understand the processes that cause emesis in abnormal gravitational regimes.     

The mechanics of air-breathing in anuran larvae: implications to the development of amphibians in microgravity.

Because of their rapid development, amphibians have been important model organisms in studies of how microgravity affects vertebrate growth and differentiation. Both urodele (salamanders) and anuran (frogs and toads) embryos have been raised in orbital flight, the latter several times. The most commonly reported and striking effects of microgravity on tadpoles are not in the vestibular system, as one might suppose, but in their lungs and tails. Pathological changes in these organs disrupt behavior and retard larval growth. What causes malformed (typically lordotic) tadpoles in microgravity is not known, nor have axial pathologies been reported in every flight experiment. Lung pathology, however, has been consistently observed and is understood to result from the failure of the animals to inflate their lungs in a timely and adequate fashion. We suggest that malformities in the axial skeleton of tadpoles raised in microgravity are secondary to problems in respiratory function. We have used high speed videography to investigate how tadpoles breathe air in the 1G environment. The video images reveal alternative species-specific mechanisms, that allow tadpoles to separate air from water in less that 150 ms. We observed nothing in the biomechanics of air-breathing in 1G that would preclude these same mechanisms from working in microgravity. Thus our kinematic results suggest that the failure of tadpoles to inflate their lungs properly in microgravity is due to the tadpoles' inability to locate the air-water interface and not a problem with the inhalation mechanism per se.     

Sodium and potassium uptake of Ulva – Application of marine macro-algae for space agriculture

The treatment of sodium, Na, and potassium, K, presents a challenge in space agriculture material recycling, as humans require Na and plants cannot grow at high Na concentrations. Hence, we are proposing the use of marine macro-algae to harvest K and other minerals from composted human waste. Ulva was selected for this feasibility study, since it tolerates a wide range of salinity levels. Growth capability of Ulva was examined under various total salinity levels and proportions of Na and K in the incubation medium. A homeostatic feature of Ulva was found in its intra-cellular concentration of Na and K, and in the intra-cellular ratio between Na and K (at 0.58 ± 0.30, lower than that of human metabolic waste). Intracellular concentration of K in Ulva is 20 times higher than seawater. Because of these characteristics, Ulva is a good candidate species for space agriculture.     

Allometry in vestibular responses of anurans

Frogs and toads turn either their heads or bodies opposite to angular accelerations applied around the yaw axis. Thresholds exist for the minimum angular acceleration that induces this vestibulomotor response in individual frogs. These thresholds were recorded for several anuran species that cover a broad range of sizes and life styles. Interspecific variation in the magnitude of the thresholds, which correlated with the ecology and behavior of the species, was documented. Also an allometric relationship was observed between this threshold and body size; the larger the frog, the lower the threshold. In many species, the threshold value for reflexive vestibulomotor responses to angular acceleration was proportional to the -0.4 (+/-0.2) power of body mass. Physical dimensions of the semicircular canals determine, in part, vestibular sensitivity to angular acceleration. Hence changes with growth in the semicircular canals are believed to contribute to the slope of -0.4. The biological significance of this allometry in vestibular responses is discussed and compared to trends in vestibular sensitivity and semicircular canal morphology of other vertebrate classes.     

A role of cytoskeletal structure of cortical cells in the gravity-regulated formation of a peg in cucumber seedlings.

Seedlings of cucurbitaceous plants develop a protuberant tissue, or peg, on the lower side of the transition region between root and hypocotyl when germinated in a horizontal position. Peg develops due to a change in growth polarity of the cortical cells. We have examined the role of the cytoskeletal structure in peg formation of cucumber seedlings. We observed that in both peg and normal cortical cells of 36 h-old seedlings the microtubules (MTs) were arranged perpendicular to the longitudinal axis of the elongating cells. Application of colchicine perturbed the MTs structure and inhibited the formation of pegs. In 20 h-old seedlings, MTs in cortical cells destined to be a peg tissue had no preferential organization, whereas MTs in normal cortical cells were transversely oriented. After 24 h, the MTs in future peg cells were arranged similar to those of 36 h-old seedlings, although the initiation of peg tissue was not yet visible. These results suggest that reorganization of MTs is required for peg formation and causes the change in growth polarity of the cortical cells.