Residual nutational activity of the sunflower hypocotyl in simulated weightlessness

Does gravity drive circumnutation? One model ascribes hypocotylcircumnutation to a continuing series of geotropic responseseach of which overshoots thereby maintaining a sustained oscillation.However, some features of the observed movements are not easilyreconciled with the model. The critical feature of this modelis the requirement that circumnutation must exhibit an absolutedependence on a g-force. Experiments with Helianthns annum onhorizontal clinostats demonstrated an 80% reduction in the amplitudeof hypocotyl circumnutation (compared with upright plants atone g) although the oscillations continued at simulated "zerog". It is not certain that the clinostat environment adequatelysimulates the weightless environment of space but, if it does,we may expect a space experiment to demonstrate that hypocotylnutation in Helianthus annuus is not fully dependent on gravity. (Received October 13, 1978; )     

家蚕动力蛋白轻链8基因克隆及其对重力的响应

克隆家蚕动力蛋白轻链8(dynein light chain 8, Dlc8)基因开放阅读框架并对其序列进行分析．探讨Dlc8基因在家蚕胚胎、头、丝腺、中肠、皮肤、血液、脂肪和马氏管等组织中的分布．在细胞水平,应用RT-PCR和实时定量RT-PCR方法分析大梯度强磁场(large gradient high magnetic field, LGHMF)重力模拟环境(0 g、1 g、2 g)对家蚕Dlc8基因表达的影响．在整体水平,应用实时定量RT-PCR方法分析Dlc8基因在家蚕胚胎反转期和整个胚胎期对LGHMF模拟失重环境的响应．克隆的家蚕Dlc8基因开放阅读框架长度为270 bp,编码89个氨基酸．家蚕Dlc8基因推导的氨基酸序列与拟南芥(Arabidopsis thaliana)、果蝇(Drosophila melanogaster)、线虫(Caenorhabditis elegans)、热带爪蟾(Xenopus tropicalis)、小鼠(Mus musculus)、人类(Homo sapiens)等6个物种Dlc8基因的氨基酸序列同源性分别为67%、96%、91%、95%、92%、92%．信号肽分析结果显示,该蛋白质为非分泌蛋白,不存在糖基磷脂酰肌醇锚定位点．家蚕Dlc8分子质量与等电点分别为10.34 ku和6.81．Dlc8基因在家蚕的胚胎、头、丝腺、中肠、皮肤、血液、脂肪、马氏管中稳定表达．在细胞水平,家蚕Dlc8基因表达对重力变化较敏感,对磁场变化不敏感．在整体水平,Dlc8基因在家蚕胚胎发育的不同时期对重力的响应不同．整个胚胎发育期Dlc8基因在模拟失重条件下表达量与对照组接近．家蚕Dlc8基因可以作为重力生物学效应研究的分子靶标．该研究为深入探讨家蚕Dlc8基因重力生物学效应机制奠定了基础．     

Effect of Gravity Changes on the Cyanobacterium Synechocystis sp. PCC 6803

The impact of hypergravity and simulated weightlessness were studied to check whether cyanobacteria perceive changes of gravity as stress. Hypergravity generated by a low-speed centrifuge increased slightly the overall activity of dehydrogenases, but the increase was the same for 90 g and 180 g. The protein pattern did not show qualitative alterations during hypergravity treatment up to 180 g. Cells of Synechocystis PCC 6803 subjected to common stressors like salt, heat, and light clearly accumulated at least four general stress proteins (25, 31, 34, and 63 kDa, respectively). Three of these proteins could also be detected after hypergravity, but in such small amounts that their occurrence could only be taken as a weak indication of stress. Low-molecular-weight stress metabolites were not synthesized in response to hypergravity, indicating that this gravity change was unable to activate the osmotic signal transduction chain. Gravity-dependent alterations were observed only during simulated weightlessness (generated by a fast-rotating clinostat). The glutamate/glutamine ratio was significantly shifted toward a higher glutamine portion. Altogether, the results may indicate that moderate changes of gravity were hardly, if ever, sensed as stress by cyanobacteria. Received: 20 May 1997 / Accepted: 25 June 1997     

Effect of simulated and real weightlessness on early regeneration stages of Brassica napus protoplasts

Summary Results from experiments using protoplasts in space, performed on the Biokosmos 9 satellite in 1989 and on the Space Shuttle on the IML-1-mission in 1992 and S/MM-03 in 1996, are presented. This paper focuses on the observation that the regeneration capacity of protoplasts is lower under micro-g conditions than under 1 g conditions. These aspects have been difficult to interpret and raise new questions about the mechanisms behind the observed effects. In an effort to try to find a key element to the poor regeneration capacity, ground-based studies were initiated focusing on the effect of the variable organization and quantity of corticular microtubules (CMTs) as a consequence of short periods of real and simulated weightlessness. The new results demonstrated the capacity of protoplasts to enter division, confirming the findings in space that this was affected by gravity. The percentage of dividing cells significantly decreased as a result of exposure to simulated weightlessness on a 2-D clinostat. Similar observations were made when comparing the wall components, which confirmed that the reconstitution of the cell wall was retarded under both space conditions and simulated weightlessness. The peroxidase activity in protoplasts exposed to microgravity was slightly decreased in both 0 g and 1 g flight samples compared with the ground controls, whereas activity in the protoplasts exposed to simulated weightlessness was similar to activity in the 1 g control. The observation that protoplasts had randomized and more sparse corticular microtubules when exposed to various forms of simulated and real weightlessness on a free-fall machine on the ground could indicate that the low division capacity in 0 g protoplasts was correlated with an abnormal CMT array in these protoplasts. This study has increased our knowledge of the more basic biochemical and cell biological aspects of g effects. This is an important link in preparation for the new space era, when it will be possible to follow the growth of single cells and tissue cultures for generations under microgravity conditions on the new International Space Station, which will be functional on a permanent basis from the year 2003.     

Gravitropism of hypocotyls of wild-type and starch-deficient Arabidopsis seedlings in spaceflight studies

The major purpose of this spaceflight project was to investigate the starch-statolith hypothesis for gravity perception, and a secondary goal was to study plant growth and development under spaceflight conditions. This research was based on our ground studies of gravity perception in the wild type and three starch-deficient (one starchless and two reduced starch) mutants of Arabidopsis thaliana (L.) Heynh. Dark-grown seedlings that developed in microgravity were given one of several (30 min, 60 min, or 90 min) 1-g stimuli by an on-board centrifuge, and additional controls for seedling development also were performed. These latter control experiments included a morphological study of plants that developed in space in microgravity (F μg), in space on a centrifuge (F 1g), on the ground (G 1g), and on a rotating clinostat on the ground. Since elevated levels of ethylene were reported in the spacecraft atmosphere, additional controls for morphology and gravitropism with added ethylene also were performed. While exogenous ethylene reduced the absolute magnitude of the response in all four strains of Arabidopsis, this gas did not appear to change the relative graviresponsiveness among the strains. The relative response of hypocotyls of microgravity-grown seedlings to the stimuli provided by the in-flight centrifuge was: wild type > starch-deficient mutants. Although the protoplast pressure model for gravity perception cannot be excluded, these results are consistent with a statolith-based model for perception in plants. Received: 12 February 1999 / Accepted: 9 March 1999     

A hypergravity environment increases chloroplast size,photosynthesis, and plant growth in the moss Physcomitrella patens

The physiological and anatomical responses of bryophytes to altered gravity conditions will provide crucial information for estimating how plant physiological traits have evolved to adapt to significant increases in the effects of gravity in land plant history. We quantified changes in plant growth and photosynthesis in the model plant of mosses, Physcomitrella patens, grown under a hypergravity environment for 25 days or 8 weeks using a custom-built centrifuge equipped with a lighting system. This is the first study to examine the response of bryophytes to hypergravity conditions. Canopy-based plant growth was significantly increased at 10×g, and was strongly affected by increases in plant numbers. Rhizoid lengths for individual gametophores were significantly increased at 10×g. Chloroplast diameters (major axis) and thicknesses (minor axis) in the leaves of P. patens were also increased at 10×g. The area-based photosynthesis rate of P. patens was also enhanced at 10×g. Increases in shoot numbers and chloroplast sizes may elevate the area-based photosynthesis rate under hypergravity conditions. We observed a decrease in leaf cell wall thickness under hypergravity conditions, which is in contrast to previous findings obtained using angiosperms. Since mosses including P. patens live in dense populations, an increase in canopy-based plant numbers may be effective to enhance the toughness of the population, and, thus, represents an effective adaptation strategy to a hypergravity environment for P. patens.

     

Gravitropic moss cells default to spiral growth on the clinostat and in microgravity during spaceflight

In addition to shoots and roots, the gravity (g)-vector orients the growth of specialized cells such as the apical cell of dark-grown moss protonemata. Each apical cell of the moss Ceratodon purpureus senses the g-vector and adjusts polar growth accordingly producing entire cultures of upright protonemata (negative gravitropism). The effect of withdrawing a constant gravity stimulus on moss growth was studied on two NASA Space Shuttle (STS) missions as well as during clinostat rotation on earth. Cultures grown in microgravity (spaceflight) on the STS-87 mission exhibited two successive phases of non-random growth and patterning, a radial outgrowth followed by the formation of net clockwise spiral growth. Also, cultures pre-aligned by unilateral light developed clockwise hooks during the subsequent dark period. The second spaceflight experiment flew on STS-107 which disintegrated during its descent on 1 February 2003. However, most of the moss experimental hardware was recovered on the ground, and most cultures, which had been chemically fixed during spaceflight, were retrieved. Almost all intact STS-107 cultures displayed strong spiral growth. Non-random culture growth including clockwise spiral growth was also observed after clinostat rotation. Together these data demonstrate the existence of default non-random growth patterns that develop at a population level in microgravity, a response that must normally be overridden and masked by a constant g-vector on earth.     

Influences of root distribution and growth on predicted water uptake and interspecific competition

Summary Root distribution and growth measured in the field were incorporated into a water uptake model for the CAM succulent Agave deserti and its nurse plant Hilaria rigida, a common desert bunchgrass. Agave deserti responds to the infrequent rainfalls of the Sonoran Desert by extending its existing established roots and by producing new roots. Most of such root growth was completed within one month after soil rewetting, total root length of A. deserti increasing by 84% for a seedling and by 58% for a mediumsized plant in the summer. Root growth in the winter with its lower soil temperatures was approximately half as much as in the summer. For a 15-year period, predicted annual root growth of A. deserti varied more than 18-fold because of annual variations in rainfall amount and pattern as well as seasonal variation in soil temperature. Predicted annual water uptake varied 47-fold over the same period. The nurse plant, which is crucial for establishment of A. deserti seedlings, reduced seedling water uptake by 38% during an average rainfall year. Lowering the location of the root system of a medium-sized A. deserti by 0.24 m reduced its simulated annual water uptake by about 25%, reflecting the importance of shallow roots for this desert succulent. Lowering the root system of a medium-sized H. rigida by 0.28 m increased the simulated annual water uptake of an associated A. deserti seedling by 17%, further indicating the influence of root overlap on competition for water.     

Simulated microgravity impairs respiratory burst activity in human promyelocytic cells

Summary The concept of microgravity (free-fall) influencing cellular functions in nonadherent cells has not been a part of mainstream scientific thought. Utilizing rotating wall vessels (RWVs) to generate simulated microgravity conditions, we found that respiratory burst activity was significantly altered in nonadherent promyelocytic (HL-60) cells. Specifically, HL-60 cells in simulated microgravity for 6, 19, 42, 47, and 49 d had 3.8-fold fewer cells that were able to participate in respiratory burst activity than cells from 1×g cultures (P=0.0011, N=5). The quantity of respiratory burst products from the cells in simulated microgravity was also significantly reduced. The fold increase over controls in mean fluorescence intensities for oxidative products from cells in microgravity was 1.1±0.1 versus 1.8±0.3 for cells at 1 ×g (P=0.013, N=4). Furthermore, the kinetic response for phorbol ester-stimulated burst activity was affected by simulated microgravity. These results demonstrate that simulated microgravity alters an innate cellular function (burst activity). If respiratory burst activity is impaired by true microgravity, then recovery from infections during spaceflight could be delayed. Finally, RWVs provide an excellent model for investigating the mechanisms associated with microgravity-induced changes in nonadherent cells.     

Metabolic flux and cell cycle analysis indicating new mechanism underlying process oscillation in continuous ethanol fermentation with Saccharomyces cerevisiae under VHG conditions

Process oscillation characterized by long oscillation period and large oscillation amplitude was observed in continuous ethanol fermentation with Saccharomyces cerevisiae under very high gravity conditions. Metabolic flux analysis was applied to the fermentation system, and the results indicated that carbon flux distributions at the metabolic notes oscillated, correspondingly, and the root reason for the process oscillation was the intracellular metabolism of yeast cells. Cell cycle analysis with the flow cytometry showed that no cell-cycle-dependent synchronization of the daughter and mother cells occurred within the duration of the oscillation, and thus different mechanism existed compared with the oscillation observed in the continuous culture of Saccharomyces cerevisiae and triggered by the synchronization of the daughter and mother cells under specific conditions. Furthermore, the overall metabolic activity of the yeast cells was examined, which was found not exactly out of phase but lag behind ethanol concentration that accumulated within the fermentation system and its inhibition on the yeast cells as well, which supported the mechanistic speculation for the process oscillation: the lag response of yeast cells to ethanol inhibition.     

Influence of increased mechanical loading by hypergravity on the microtubule cytoskeleton and prostaglandin E2 release in primary osteoblasts

Cells respond to a wide range of mechanical stimuli such as fluid shear and strain, although the contribution of gravity to cell structure and function is not understood. We hypothesized that bone-forming osteoblasts are sensitive to increased mechanical loading by hypergravity. A centrifuge suitable for cell culture was developed and validated, and then primary cultures of fetal rat calvarial osteoblasts at various stages of differentiation were mechanically loaded using hypergravity. We measured microtubule network morphology as well as release of the paracrine factor prostaglandin E₂ (PGE₂). In immature osteoblasts, a stimulus of 10x gravity (10 g) for 3 h increased PGE₂ 2.5-fold and decreased microtubule network height 1.12-fold without affecting cell viability. Hypergravity (3 h) caused dose-dependent (5–50 g) increases in PGE₂ (5.3-fold at 50 g) and decreases (1.26-fold at 50 g) in microtubule network height. PGE₂ release depended on duration but not orientation of the hypergravity load. As osteoblasts differentiated, sensitivity to hypergravity declined. We conclude that primary osteoblasts demonstrate dose- and duration-dependent sensitivity to gravitational loading, which appears to be blunted in mature osteoblasts. mechanotransduction; differentiation; bone     

Hypergravity prevents seed production in <Emphasis Type="Italic">Arabidopsis</Emphasis> by disrupting pollen tube growth

How tightly land plants are adapted to the gravitational force (g) prevailing on Earth has been of interest because unlike many other environmental factors, g presents as a constant force. Ontogeny of mature angiosperms begins with an embryo that is formed after tip growth by a pollen tube delivers the sperm nucleus to the egg. Because of the importance to plant fitness, we have investigated how gravity affects these early stages of reproductive development. Arabidopsis thaliana (L.) Heynh. plants were grown for 13 days prior to being transferred to growth chambers attached to a large diameter rotor, where they were continuously exposed to 2-g or 4-g for the subsequent 11 days. Plants began flowering 1 day after start of the treatments, producing hundreds of flowers for analysis of reproductive development. At 4-g, Arabidopsis flowers self-pollinated normally but did not produce seeds, thus derailing the entire life cycle. Pollen viability and stigma esterase activity were not compromised by hypergravity; however, the growth of pollen tubes into the stigmas was curtailed at 4-g. In vitro pollen germination assays showed that 4-g average tube length was less than half that for 1-g controls. Closely related Brassica rapa L., which produces seeds at 4-g, required forces in excess of 6-g to slow in vitro tube growth to half that at 1-g. The results explain why seed production is absent in Arabidopsis at 4-g and point to species differences with regard to the g-sensitivity of pollen tube growth.     

Gravitational force modulates muscle activity during mechanical oscillation of the tibia in humans

Mechanical oscillation (vibration) is an osteogenic stimulus for bone in animal models and may hold promise as an anti-osteoporosis measure in humans with spinal cord injury (SCI). However, the level of reflex induced muscle contractions associated with various loads (g force) during limb segment oscillation is uncertain. The purpose of this study was to determine whether certain gravitational loads (g forces) at a fixed oscillation frequency (30 Hz) increases muscle reflex activity in individuals with and without SCI. Nine healthy subjects and two individuals with SCI sat with their hip and knee joints at 90° and the foot secured on an oscillation platform. Vertical mechanical oscillations were introduced at 0.3, 0.6, 1.2, 3 and 5g force for 20 s at 30 Hz. Non-SCI subjects received the oscillation with and without a 5% MVC background contraction. Peak soleus and tibialis anterior (TA) EMG were normalized to M-max. Soleus and TA EMG were <2.5% of M-max in both SCI and non-SCI subjects. The greatest EMG occurred at the highest acceleration (5g). Low magnitude mechanical oscillation, shown to enhance bone anabolism in animal models, did not elicit high levels of reflex muscle activity in individuals with and without SCI. These findings support the g force modulated background muscle activity during fixed frequency vibration. The magnitude of muscle activity was low and likely does not influence the load during fixed frequency oscillation of the tibia.     

Limited period of graviresponsiveness in germinating spores of Ceratopteris richardii

Rhizoids of the fern Ceratopteris richardii Brogn. usually emerge 40 h after germination is initiated by light, and more than 90% of them emerge growing in a downward direction. However, when the spores are germinated on a clinostat, the emerging rhizoids show no preferential orientation. This indicates that under normal 1 · g conditions the initial growth direction of rhizoids can be oriented by gravity. If the orientation of the spores is changed 3 h or less after the start of germination, the growth direction of most emerging rhizoids becomes downward relative to the new orientation. However, if the orientation of the spores is changed by 180° 8 h or more after germination is initiated by light, most rhizoids emerge growing upward; i.e., the same direction as if there had been no orientation change. Emerged rhizoids also do not change their direction of growth if their orientation is changed. These results indicate that the growth direction of emerging rhizoids is set by gravity prior to actual emergence, and that the time of full orientation responsiveness is limited to a period ranging from the initiation of germination to about 3–4 h after the start of germination. There is a gravity-oriented nuclear movement beginning at about 13 h after germination, and this movement appears to predict the initial growth direction of rhizoids.These studies were made possible by grant NAGW 1519 to S.J.R. and grant NGT-51065 to E.S.E., both from the National Aeronautics and Space Administration.     

Effects of altered gravity on the actin and microtubule cytoskeleton of human SH-SY5Y neuroblastoma cells

Summary. Human SH-SY5Y neuroblastoma cells were used to study the effects of altered gravity on the actin and microtubule cytoskeleton dynamics. A cholinergic stimulation of the cells during a 6 min period of changing gravity (3 parabolas) resulted in an enhanced actin-driven protrusion of evoked lamellipodia. Likewise, the spontaneous protrusive activity of nonactivated cells was promoted during exposure to changing gravity (6 up to 31 parabolas). Ground-based experiments revealed a similar enhancement of the spontaneous and evoked lamellar protrusive activity when the cells were kept at 2 g hypergravity for at least 6 min. This gravity response was independent of the direction of the acceleration vector in respect to the cells. Exposure of the cells to “simulated weightlessness” (clinorotation) had no obvious influence on this type of lamellar actin cytoskeleton dynamics. A 20 min exposure of the cells to simulated weightlessness or to changing gravity (6 to 31 parabolas) – but not to 2 g (hypergravity, centrifugation) – resulted in an altered arrangement of microtubules indicated by bending, turning, and loop formation. A similar altered arrangement was shown by microtubules which had polymerized into lamellipodia after release from a taxol block at simulated weightlessness (clinorotation) or during changing gravity (5 parabolas). Our data suggest that in human SH-SY5Y neuroblastoma cells, microgravity affects the dynamics and spatial arrangement of microtubules but has no influence on the Rac-controlled lamellar actin cytoskeleton dynamics and cell spreading. The latter, however, seems to be promoted at hypergravity. Correspondence and reprints: Cell and Developmental Neurobiology, Institute of Zoology, University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Federal Republic of Germany.     

Changes in gravity rapidly alter the magnitude and direction of a cellular calcium current

In single-celled spores of the fern Ceratopteris richardii, gravity directs polarity of development and induces a directional, trans-cellular calcium (Ca²⁺) current. To clarify how gravity polarizes this electrophysiological process, we measured the kinetics of the cellular response to changes in the gravity vector, which we initially estimated using the self-referencing calcium microsensor. In order to generate more precise and detailed data, we developed a silicon microfabricated sensor array which facilitated a lab-on-a-chip approach to simultaneously measure calcium currents from multiple cells in real time. These experiments revealed that the direction of the gravity-dependent polar calcium current is reversed in less than 25 s when the cells are inverted, and that changes in the magnitude of the calcium current parallel rapidly changing g-forces during parabolic flight on the NASA C-9 aircraft. The data also revealed a hysteresis in the response of cells in the transition from 2g to micro-g in comparison to cells in the micro-g to 2-g transition, a result consistent with a role for mechanosensitive ion channels in the gravity response. The calcium current is suppressed by either nifedipine (calcium-channel blocker) or eosin yellow (plasma membrane calcium pump inhibitor). Nifedipine disrupts gravity-directed cell polarity, but not spore germination. These results indicate that gravity perception in single plant cells may be mediated by mechanosensitive calcium channels, an idea consistent with some previously proposed models of plant gravity perception.     

The distribution of myelin basic protein in subcellular fractions of developing Jimpy mouse brain.

Abstract— The amount of myelin basic protein in jimpy mutants and unaffected littermates was measured by radioimmunoassay during the period of most active myelination (11-21 days). This protein was examined in whole brain homogenates and in four subcellular fractions (nuclear, 900 g pellet; heavy membrane, 11,500 g pellet; microsomal, 100,000 g pellet; and cytosol, 100,000g supernatant solution). At all ages examined, the mutants, which have very little myelin in the CNS, had only about 2% the amount of basic protein found in controls. As expected, the amount of myelin basic protein increased 4-fold in the control animals during the developmental period studied. This was not the case in the jimpy mutants, where little increase in the whole brain basic protein was observed. In the jimpy mutants, all of the fractions had significantly less basic protein than control fractions, except the cytosol, where the amounts of basic protein were similar in controls and mutants. These results are discussed with respect to possible mechanisms of myelination and the site of the genetic lesion.     

Gravitropic bending of cress roots without contact between amyloplasts and complexes of endoplasmic reticulum

The polar arrangement of cell organelles in Lepidium root statocytes is persistently converted to a physical stratification during lateral centrifugation (the centrifugal force acts perpendicular to the root long axis) or by apically directed centrifugation combined with cytochalasin-treatment. Lateral centrifugation (10 min, 60 min at 10\g or 50\g) causes displacement of amylplasts to the centrifugal anticlinal cell wall and shifting of the endoplasmic reticulum (ER) complex to the centripetal distal cell edge. After 60 min of lateral centrifugation at 10\g or 50\g all roots show a clear gravitropic curvature. The average angle of curvature is about 40° and corresponds to that of roots stimulated gravitropically in the horizontal position at 1\g in spite of the fact that the gravistimulus is 10-or 50-fold higher. Apically directed centrifugation combined with cytochalasin B (25 g\ml^-1) or cytochalasin D (2.5 g\ml^-1) incubation yields statocytes with the amyloplasts sedimented close to the centrifugal periclinal cell wall and ER cisternae accumulated at the proximal cell pole. Gravitropic stimulation for 30 min in the horizontal position at 1\g and additional 3 h rotation on a clinostat result in gravicurvature of cytochalasin B-treated centrifuged (1 h at 50\g) roots, but because of retarded root growth the angle of curvature is lower than in control roots. Cytochalasin D-treatment during centrifugation (20 min at 50\g) does not affect either root growth or gravicurvature during 3 h horizontal exposure to 1\g relative to untreated roots. As lateral centrifugation enables only short-term contact between the amyloplasts and the distal ER complex at the onset of centrifugation and apically directed centrifugation combined with cytochalasin-treatment even exclude any contact the integrity of the distal cell pole need not necessarily be a prerequisite for graviperception in Lepidium root statocytes.Abbreviations CB cytochalasin B - CD cytochalasin D - ER endoplasmic reticulum - g gravitational acceleration     

Enhancement of phototropic response to a range of light doses in Triticum aestivum coleoptiles in clinostat-simulated microgravity

The phototropic dose-response relationship has been determined for Triticum aestivum cv. Broom coleoptiles growing on a purpose-built clinostat apparatus providing gravity compensation by rotation about a horizontal axis at 2 rev·min^-1. These data are compared with data sets obtained with the clinostat axis vertical and stationary, as a 1·g control, and rotating vertically to examine clinostat effects other than gravity compensation. Triticum at 1·g follows the wellestablished pattern of other cereal coleoptiles with a first positive curvature at low doses, followed by an indifferent response region, and a second positive response at progressively increasing doses. However, these response regions lie at higher dose levels than reported for Avena. There is no significant difference between the responses observed with the clinostat axis vertical in the rotating and stationary modes, but gravity compensation by horizontal rotation increases the magnitude of first and second positive curvatures some threefold at 100 min after stimulation. The indifferent response is replaced by a significant curvature towards the light source, but remains apparent as a reduced curvature response at these dose levels.     

Hypergravity induces reorientation of cortical microtubules and modifies growth anisotropy in azuki bean epicotyls

We examined the changes in the orientation of cortical microtubules during the hypergravity-induced modification of growth anisotropy (inhibition of elongation growth and promotion of lateral growth) in azuki bean (Vigna angularis Ohwi et Ohashi) epicotyls. The percentage of cells with transverse microtubules was decreased, while that with longitudinal microtubules was increased, in proportion to the logarithm of the magnitude of gravity. The percentage of cells with longitudinal microtubules showed an increase within 0.5 h of transfer of the 1g-grown seedlings to a 300g-hypergravity condition. Lanthanum and gadolinium, blockers of calcium channels, nullified the modification of growth anisotropy and reorientation of microtubules by hypergravity. Horizontal and acropetal hypergravity modified growth anisotropy and reorientation of microtubules, as did basipetal hypergravity, and these changes were not seen in the presence of lanthanum or gadolinium. These results suggest that hypergravity changes activities of lanthanum- and gadolinium-sensitive calcium channels independently of its direction, which may lead to reorientation of cortical microtubules and modification of growth anisotropy in azuki bean epicotyls.