Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： doi:10.3390/plants11030465

DOI： 10.1016/j.jplph.2021.153409

DOI： 10.1089/ast.2019.2140

DOI： 10.3390/plants9050590

<p>We examined the effects of hypergravity on nuclear positioning in epidermal cells of azuki bean (<i>Vigna angularis</i>) epicotyls. The nucleus was positioned almost in the center of the cell under 1 <i>G</i> conditions. When the epicotyls were exposed to basipetal hypergravity by centrifugation, the nucleus was displaced toward the centrifugal side of the cell in a linear dose-response manner. The nuclear displacement started within 20 min by exposure to basipetal hypergravity at 300 <i>G</i>, and reached ca. 35% from the centrifugal edge of the cell after 2 h. The displaced nucleus recentered by removal of hypergravity stimuli. The nucleus was also displaced by acropetal hypergravity at the similar degree as basipetal hypergravity. The displacement by hypergravity of the nucleus was stimulated, when actin filaments were disrupted by cytochalasin D treatment. These results suggest that the positioning of the nucleus in epidermal cells is maintained by actin filaments, which is affected by gravity in azuki bean epicotyls.</p>

DOI： 10.2187/bss.33.1

CiNii Article

DOI： 10.1080/15592324.2017.1422468

PubMed

Publishing type：Research paper (scientific journal)  

We carried out a space experiment, denoted as Aniso Tubule, to examine the effects of microgravity on the growth anisotropy and cortical microtubule dynamics in Arabidopsis hypocotyls, using lines in which microtubules are visualized by labeling tubulin or microtubule-associated proteins (MAPs) with green fluorescent protein (GFP). In all lines, GFP-tubulin6 (TUB6)-, basic proline-rich protein1 (BPP1)-GFP- and spira1-like3 (SP1L3)-GFP-expressing using a constitutive promoter, and spiral2 (SPR2)-GFP- and GFP-65 kDa MAP-1 (MAP65-1)-expressing using a native promoter, the length of hypocotyls grown under microgravity conditions in space was longer than that grown at 1 g conditions on the ground. In contrast, the diameter of hypocotyls grown under microgravity conditions was smaller than that of the hypocotyls grown at 1 g. The percentage of cells with transverse microtubules was increased under microgravity conditions, irrespective of the lines. Also, the average angle of the microtubules with respect to the transverse cell axis was decreased in hypocotyls grown under microgravity conditions. When GFP fluorescence was quantified in hypocotyls of GFP-MAP65-1 and SPR2-GFP lines, microgravity increased the levels of MAP65-1, which appears to be involved in the maintenance of transverse microtubule orientation. However, the levels of SPR2 under microgravity conditions were comparable to those at 1 g. These results suggest that the microgravity-induced increase in the levels of MAP65-1 is involved in increase in the transverse microtubules, which may lead to modification of growth anisotropy, thereby developing longer and thinner hypocotyls under microgravity conditions in space.

DOI： 10.1111/ppl.12640

PubMed

<p>The effects of hypergravity on growth and dynamics of actin filaments were examined in azuki bean (<i>Vigna angularis</i>) epicotyls. Elongation growth occurred mainly in the apical region of epicotyls, which was inhibited by hypergravity at 300 <i>G</i>. The density of actin filaments in epidermal cells decreased from the apical to the basal regions of epicotyls, irrespective of the gravitational conditions, and in the apical region of epicotyls, hypergravity decreased the density. Actin filaments were arranged with longitudinal or radial direction in the epidermal cells of apical region of 1 <i>G</i>-grown epicotyls. On the other hand, actin filaments with transverse direction were observed in basal region of epicotyls grown at 1 <i>G</i>. Similar changes in the arrangement of actin filaments toward the basal region were observed even under hypergravity conditions. Hypergravity had no effects on the growth and reorientation of cortical microtubules, when actin filaments were disrupted by cytochalasin D treatment. These results suggest that modification of dynamics of actin filaments is responsible for reorientation of cortical microtubules, which leads to inhibition of elongation growth in azuki bean epicotyls under hypergravity conditions.</p>

DOI： 10.2187/bss.32.11

CiNii Article

Publishing type：Research paper (scientific journal)  

We investigated the effects of microgravity environment on growth and plant hormone levels in dark-grown rice shoots cultivated in artificial 1 g and microgravity conditions on the International Space Station (ISS). Growth of microgravity-grown shoots was comparable to that of 1 g-grown shoots. Endogenous levels of indole-3-acetic acid (IAA) in shoots remained constant, while those of abscisic acid (ABA), jasmonic acid (JA), cytokinins (CKs) and gibberellins (GAs) decreased during the cultivation period under both conditions. The levels of auxin, ABA, JA, CKs and GAs in rice shoots grown under microgravity conditions were comparable to those under 1 g conditions. These results suggest microgravity environment in space had minimal impact on levels of these plant hormones in rice shoots, which may be the cause of the persistence of normal growth of shoots under microgravity conditions. Concerning ethylene, the expression level of a gene for 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, the key enzyme in ethylene biosynthesis, was reduced under microgravity conditions, suggesting that microgravity may affect the ethylene production. Therefore, ethylene production may be responsive to alterations of the gravitational force.

DOI： 10.1111/ppl.12591

PubMed

Publishing type：Research paper (scientific journal)  

We performed a phenotypic screening of confirmed homozygous T-DNA insertion lines in Arabidopsis for cell wall extensibility, in an attempt to identify genes involved in the regulation of cell wall mechanical properties. Seedlings of each line were cultivated and the cell wall extensibility of their hypocotyls was measured with a tensile tester. Hypocotyls of lines with known cell wall-related genes showed higher or lower extensibility than those of the wild-type at high frequency, indicating that the protocol used was effective. In the first round of screening of randomly selected T-DNA insertion lines, we identified ANTHOCYANINLESS2 (ANL2), a gene involved in the regulation of cell wall mechanical properties. In the anl2 mutant, the cell wall extensibility of hypocotyls was significantly lower than that of the wild-type. Levels of cell wall polysaccharides per hypocotyl, particularly cellulose, increased in anl2. Microarray analysis showed that in anl2, expression levels of the major peroxidase genes also increased. Moreover, the activity of ionically wall-bound peroxidases clearly increased in anl2. The activation of peroxidases as well as the accumulation of cell wall polysaccharides may be involved in decreased cell wall extensibility. The approach employed in the present study could contribute to our understanding of the mechanisms underlying the regulation of cell wall mechanical properties. (C) 2016 Elsevier GmbH. All rights reserved.

DOI： 10.1016/j.jplph.2015.11.011

PubMed

The present experiment aims to clarify the roles of 65 kDa microtubule-associated protein-1 (MAP65-1) and basic proline-rich protein1 (BPP1), which are involved in the maintenance of transverse microtubule orientation, in gravity resistance, using green fluorescent protein (GFP)-expressing Arabidopsis lines. Hypergravity at 300 <i>G</i> inhibited elongation growth and promoted lateral expansion of epidermal cells in the subapical region of hypocotyls in GFP-MAP65-1 line expressing by native promoter and BPP1-GFP line expressing by a constitutive cauliflower mosaic virus <i>35S</i> promoter. In BPP1-GFP line, hypergravity showed smaller effects on modification of growth anisotropy than wild type. Also, hypergravity induced reorientation of cortical microtubules from transverse to longitudinal directions in both lines. However, in BPP1-GFP line, hypergravity showed smaller effects on reorientation of cortical microtubules. When the expression levels of MAP65-1 were determined by analyzing GFP fluorescence in hypocotyls of GFP-MAP65-1 line, hypergravity decreased the levels of MAP65-1 in the subapical region, where hypergravity modified growth anisotropy and orientation of cortical microtubules. These results indicate that the regulation of levels of MAP65-1 and BPP1 is involved in the hypergravity-induced reorientation of cortical microtubules, which may lead to modification of growth anisotropy, thereby developing a tough body against the gravitational force in Arabidopsis hypocotyls.

DOI： 10.2187/bss.30.1

CiNii Article

Publishing type：Research paper (scientific journal)  

Network structures created by hydroxycinnamate cross-links within the cell wall architecture of gramineous plants make the cell wall resistant to the gravitational force of the earth. In this study, the effects of microgravity on the formation of cell wall-bound hydroxycinnamates were examined using etiolated rice shoots simultaneously grown under artificial 1 g and microgravity conditions in the Cell Biology Experiment Facility on the International Space Station. Measurement of the mechanical properties of cell walls showed that shoot cell walls became stiff during the growth period and that microgravity suppressed this stiffening. Amounts of cell wall polysaccharides, cell wall-bound phenolic acids, and lignin in rice shoots increased as the shoot grew. Microgravity did not influence changes in the amounts of cell wall polysaccharides or phenolic acid monomers such as ferulic acid (FA) and p-coumaric acid, but it suppressed increases in diferulic acid (DFA) isomers and lignin. Activities of the enzymes phenylalanine ammonia-lyase (PAL) and cell wall-bound peroxidase (CW-PRX) in shoots also increased as the shoot grew. PAL activity in microgravity-grown shoots was almost comparable to that in artificial 1 g-grown shoots, while CW-PRX activity increased less in microgravity-grown shoots than in artificial 1 g-grown shoots. Furthermore, the increases in expression levels of some class III peroxidase genes were reduced under microgravity conditions. These results suggest that a microgravity environment modifies the expression levels of certain class III peroxidase genes in rice shoots, that the resultant reduction of CW-PRX activity may be involved in suppressing DFA formation and lignin polymerization, and that this suppression may cause a decrease in cross-linkages within the cell wall architecture. The reduction in intra-network structures may contribute to keeping the cell wall loose under microgravity conditions.

DOI： 10.1371/journal.pone.0137992

PubMed

Publishing type：Research paper (scientific journal)  

The effect of lead (Pb) on growth and mechanical properties of cell wall was investigated in rice seedlings. Caryopses of rice were germinated and grown in various concentrations of lead nitrate for 5 days at 25 degrees C in the dark. Growth of rice seedlings was suppressed by Pb ions; significant suppression was caused by low concentration of Pb as 1 mu M. Growth suppression was prominent in roots; but not clear in shoot organs, such as coleoptiles or first leaves, suggesting that roots are the primary target of Pb toxicity. The analysis of the cell wall extensibility of rice roots grown in Pb solution indicated that the cell wall extensibility was greatly decreased with increased concentration of Pb ions. These results suggest that Pb may influence the synthesis of cell wall polysaccharides, thereby decreasing the cell wall extensibility, resulting in growth suppression in rice roots.

Gravity resistance, mechanical resistance to the gravitational force, is a principal graviresponse in plants, comparable to gravitropism. The cell wall is responsible for the final step of gravity resistance. The gravity signal increases the rigidity of the cell wall via the accumulation of its constituents, polymerization of certain matrix polysaccharides due to the suppression of breakdown, stimulation of cross-link formation, and modifications to the wall environment, in a wide range of situations from microgravity in space to hypergravity. Plants thus develop a tough body to resist the gravitational force via an increase in cell wall rigidity and the modification of growth anisotropy. The development of gravity resistance mechanisms has played an important role in the acquisition of responses to various mechanical stresses and the evolution of land plants. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.phytochem.2014.08.022

PubMed

Publishing type：Research paper (scientific journal)  

The effects of hypergravity on growth and osmoregulation were examined in dark-grown azuki bean epicotyls. Elongation growth of epicotyls was promptly suppressed by hypergravity at 300g. On the contrary, the increase in fresh weight of epicotyls during incubation was not suppressed by hypergravity at 300g at least up to 6 h. Also, the level of total osmotic solutes increased during epicotyl growth for 6 h, which was not affected by hypergravity. These results suggest that azuki bean epicotyls are capable of maintaining osmoregulation even under 300g conditions for a short period. On the other hand, the increase in fresh weight of epicotyls was suppressed, in addition to suppression of elongation growth, when seedlings were treated with 300g for 24 h. The increase in level of total osmotic solutes was also inhibited by 24 h hypergravity treatment, which was accounted by the reduced levels of organic solutes, such as sugars and amino acids. Furthermore, the dry weight of seeds decreased during incubation for 24 h, but the decrease was inhibited by hypergravity at 300g. Hypergravity treatment at 300g for 24 h also increased the pH value of apoplastic solution in epicotyls. Taken together, these results suggest that the translocation of organic solutes from the seed to epicotyls is inhibited by prolonged hypergravity treatment, which may underlie the suppression of epicotyl growth, and that the breakdown of H+ gradient across the plasma membrane in epicotyl cells may be at least partly involved in the reduction of organic solute accumulation under hypergravity conditions. (C) 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2012.09.013

Publishing type：Research paper (scientific journal)  

The relationship between the formation of cell wall-bound ferulic acid (FA) and diferulic acid (DFA) and the change in activities of phenylalanine ammonia-lyase (PAL) and cell wall-bound peroxidase (CW-PRX) was studied in rice shoots. The length and the fresh mass of shoots increased during the growth period from day 4 to 6, while coleoptiles ceased elongation growth on day 5. The amounts of FA and DFA isomers as well as cell wall polysaccharides continued to increase during the whole period. The activities of PAL and CW-PRX greatly increased in the same manner during the period. There were close correlations between the PAL activity and ferulate content or between the CW-PRX activity and DFA content. The expression levels of investigated genes for PAL and putative CW-PRX showed good accordance with the activities of these enzymes. These results suggest that increases in PAL and CW-PRX activities are cooperatively involved in the formation of ferulate network in cell walls of rice shoots and that investigated genes may be, at least in part, associated with the enzyme activities. The substantial increase in such network probably causes the maturation of cell walls and thus the cessation of elongation growth of coleoptiles. (C) 2011 Elsevier GmbH. All rights reserved.

DOI： 10.1016/j.jplph.2011.10.002

PubMed

The Japan Aerospace Exploration Agency (JAXA) has been developing several life science hardware components for the Japanese experiment module ‘Kibo’ in the International Space Station (ISS). The Cell Biology Experiment Facility (CBEF) is one of these. It contains an environmental control system to regulate variables such as the temperature and humidity. It is also equipped with a centrifuge and has the ability to culture bio-specimens in a temperature range of 15 to 40°C. In biological experiments that include <i>in vitro</i> cell culture, temperature control is a key factor in the success of the experiment. Thus, we first examined the temperature data in the CBEF on the ground while changing the room temperature and cooling water temperature to investigate the ability of the CBEF. Based on the ground experiment data, we carried out life science experiments onboard Kibo. Judging from the temperature data in the CBEF under microgravity, 12 life science experiments were successfully conducted up until 2011. Considering our present data, we strongly believe that the CBEF is a functional incubator in the ISS and will contribute to future experiments.

DOI： 10.2187/bss.26.12

CiNii Article

Gravity resistance is a principal graviresponse in plants. In resistance to hypergravity, the gravity signal may be perceived by the mechanoreceptors located on the plasma membrane, and then transformed and transduced via the structural continuum or physiological continuity of cortical microtubules-plasma membrane-cell wall, leading to an increase in the cell wall rigidity as the final response. The Resist Tubule experiment, which will be conducted in the Kibo Module on the International Space Station, aims to confirm that this hypothesis is applicable to resistance to 1 <i>G</i> gravity. There are two major objectives in the Resist Tubule experiment. One is to quantify the contributions of cortical microtubules to gravity resistance using Arabidopsis tubulin mutants with different degrees of defects. Another objective is to analyze the modifications to dynamics of cortical microtubules and membrane rafts under microgravity conditions on-site by observing green fluorescent protein (GFP)-expressing Arabidopsis lines with the fluorescence microscope in the Kibo. We have selected suitable mutants, developed necessary hardware, and fixed operation procedure for the experiment.

DOI： 10.2322/tastj.10.tp_1

CiNii Article

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DOI： 10.1016/j.jplph.2010.04.001

PubMed

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Mechanical resistance to the gravitational force is a principal gravity response in plants distinct from gravitropism. In the final step of gravity resistance, plants increase the rigidity of their cell walls. Here we discuss the role of cortical microtubules, which sustain the function of the cell wall, in gravity resistance. Hypocotyls of Arabidopsis tubulin mutants were shorter and thicker than the wild-type, and showed either left-handed or right-handed helical growth at 1 g. The degree of twisting phenotype was intensified under hypergravity conditions. Hypergravity also induces reorientation of cortical microtubules from transverse to longitudinal directions in epidermal cells. In tubulin mutants, the percentage of cells with longitudinal microtubules was high even at 1 g, and it was further increased by hypergravity. The left-handed helical growth mutants had right-handed microtubule arrays, whereas the right-handed mutant had left-handed arrays. Moreover, blockers of mechanoreceptors suppressed both the twisting phenotype and reorientation of microtubules in tubulin mutants. These results support the hypothesis that cortical microtubules play an essential role in maintenance of normal growth phe-notype against the gravitational force, and suggest that mechanoreceptors are involved in signal perception in gravity resistance. Space experiments will confirm whether this view is applicable to plant resistance to 1 g gravity, as to the resistance to hypergravity. © 2010 Landes Bioscience.

DOI： 10.4161/psb.5.6.11706

PubMed

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Gravity resistance is one of two principal gravity responses in plants, comparable to gravitropism. In the final step of gravity resistance, plants increase the rigidity of their cell walls via modifications to the metabolism. Various constituents of the plasma membrane and the cytoskeleton play an important role in sustaining functions of the cell wall in gravity resistance. Mechanoreceptors located on the plasma membrane are involved in the perception of gravity signal. The perceived signal may be, at least partly, transformed and transduced via membrane sterol rafts, depending on its magnitude. Cellulose synthases and proton pumps are responsible for modifications to the cell wall metabolism and the apoplastic environment, respectively. On the other hand, the reorientation of cortical microtubules contributes to modification of growth anisotropy, which is related to gravity resistance. Also, microtubule-associated proteins are important in maintenance of the structure and induction of the reorientation of cortical microtubules. Gravity resistance in plants is thus mediated by the structural continuum or physiological continuity of cortical microtubules-plasma membrane-cell wall.

DOI： 10.2187/bss.23.131

CiNii Article

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Resistance to the gravitational force is one of two major graviresponses in plants. However, only limited information has been obtained for its mechanism. The Resist Wall experiment aims to examine the role of the cortical microtubule-plasma membrane-cell wall continuum in gravity resistance, thereby clarifying its mechanism. For this purpose, we will cultivate <i>Arabidopsis</i> mutants defective in organization of cortical microtubules (<i>tua6</i>) or synthesis of membrane sterols (<i>hmg1</i>) as well as the wild type Columbia under microgravity and 1<i>G</i> conditions in the European Modular Cultivation System on the International Space Station up to reproductive stage, and compare phenotypes on growth and development using video images. These mutants are unable to form the normal cell wall and show disordered growth pattern on Earth. However, it is expected that the defects of such mutants are rescued and they can grow and develop more or less normally under microgravity in space, where formation of the tough cell wall is not required. We will also analyze changes in expression of genes involved in formation of the continuum and properties of related cellular components under microgravity conditions. The results of the Resist Wall experiment will clarify the molecular mechanism of gravity resistance and benefit efficient plant production not only in space but on Earth.

DOI： 10.2187/bss.21.56

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Presentation type：Oral presentation (general)  

Venue：長崎  

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Venue：名古屋  

Presentation type：Oral presentation (general)  

Venue：名古屋