PubMed Health⌕ Search

Biomedical subjects

T Hoson

Publications and source records attributed to T Hoson.

At least 19 recordsLinked to original sources
PubMed2003

Hypergravity-induced changes in gene expression in Arabidopsis hypocotyls.

Under hypergravity conditions, the cell wall of stem organs becomes mechanically rigid and elongation growth is suppressed, which can be recognized as the mechanism for plants to resist gravitational force. The changes in gene expression by hypergravity treatment were analyzed in Arabidopsis hypocotyls by the differential display method, for identifying genes involved in hypergravity-induced growth suppression. Sixty-two cDNA clones were expressed differentially between the control and 300 g conditions: the expression levels of 39 clones increased, whereas those of 23 clones decreased under hypergravity conditions. Sequence analysis and database searching revealed that 12 clones, 9 up-regulated and 3 down-regulated, have homology to known proteins. The expression of these genes was further analyzed using RT-PCR. Finally, six genes were confirmed to be up-regulated by hypergravity. One of such genes encoded 3-hydroxy-3-methylglutaryl-Coenzyme A reductase (HMGR), which catalyzes a reaction producing mevalonic acid, a key precursor of terpenoids such as membrane sterols and several types of hormones. The expression of HMGR gene increased within several hours after hypergravity treatment. Also, compactin, an inhibitor of HMGR, prevented hypergravity-induced growth suppression, suggesting that HMGR is involved in suppression of Arabidopsis hypocotyl growth by hypergravity. In addition, hypergravity increased the expression levels of genes encoding CCR1 and ERD15, which were shown to take part in the signaling pathway of environmental stimuli such as temperature and water, and those of the alpha-tubulin gene. These genes may be involved in a series of cellular events leading to growth suppression of stem organs under hypergravity conditions.

Arabidopsis↗
PubMed2003

Growth restoration in azuki bean and maize seedlings by removal of hypergravity stimuli.

Hypergravity stimuli, gravitational acceleration of more than 1 x g, decrease the growth rate of azuki bean epicotyls and maize coleoptiles and mesocotyls by decreasing the cell wall extensibility via an increase in the molecular mass of matrix polysaccharides. An increase in the pH in the apoplastic fluid is hypothesized to be involved in the processes of the increase in the molecular mass of matrix polysaccharides due to hypergravity. However, whether such physiological changes by hypergravity are induced by normal physiological responses or caused by physiological damages have not been elucidated. In the present study, we examined the effects of the removal of hypergravity stimuli on growth and the cell wall properties of azuki bean and maize seedlings to clarify whether the effects of hypergravity stimuli on growth and the cell wall properties are reversible or irreversible. When the seedlings grown under hypergravity conditions at 300 x g for several hours were transferred to 1 x g conditions, the growth rate of azuki bean epicotyls and maize coleoptiles and mesocotyls greatly increased within a few hours. The recovery of growth rate of these organs was accompanied by an immediate increase in the cell wall extensibility, a decrease in the molecular mass of matrix polysaccharides, and an increase in matrix polysaccharide-degrading activities. The apoplastic pH also decreased promptly upon the removal of hypergravity stimuli. These results suggest that plants regulate the growth rate of shoots reversibly in response to hypergravity stimuli by changing the cell wall properties, by which they adapt themselves to different gravity conditions. This study also revealed that changes in growth and the cell wall properties under hypergravity conditions could be recognized as normal physiological responses of plants. In addition, the results suggest that the effects of microgravity on plant growth and cell wall properties should be reversible and could disappear promptly when plants are transferred from microgravity to 1 x g. Therefore, plant materials should be fixed or frozen on orbit for detecting microgravity-induced changes in physiological parameters after recovering the materials to earth in space experiments.

Cell Wall↗
PubMed2001

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.

Arabidopsis↗
PubMed2001

Gravitational force regulates elongation growth of Arabidopsis hypocotyls by modifying xyloglucan metabolism.

Growth of dark-grown Arabidopsis hypocotyls was suppressed under hypergravity conditions (300 g), or was stimulated under microgravity conditions in space (Space Shuttle STS-95). The mechanical extensibility of cell walls decreased and increased under hypergravity and microgravity conditions, respectively. The amounts of cell wall polysaccharides (pectin, hemicellulose-I, hemicellulose-II and cellulose) per unit length of hypocotyls increased under hypergravity conditions, and decreased under microgravity conditions. The amount and the molecular mass of xyloglucans also increased under the hypergravity conditions, while those decreased under microgravity conditions. The activity of xyloglucan-degrading enzymes extracted from hypocotyl cell walls decreased and increased under hypergravity and microgravity conditions, respectively. These results indicate that the amount and the molecular mass of xyloglucans are affected by the magnitude of gravity and that such changes are caused by changes in xyloglucan-degrading activity. Modifications of xyloglucan metabolism as well as the thickness of cell walls by gravity stimulus may be the primary event determining the cell wall extensibility, thereby regulating the growth rate of Arabidopsis hypocotyls.

Arabidopsis↗
PubMed2001

A new type of endo-xyloglucan transferase devoted to xyloglucan hydrolysis in the cell wall of azuki bean epicotyls.

A new type of xyloglucan-degrading enzyme was isolated from the cell wall of azuki bean (Vigna angularis Ohwi et Ohashi cv. Takara) epicotyls and its characteristics were determined. The enzyme was purified to apparent homogeneity by Concanavalin A (Con A)-Sepharose, cation exchange, and gel filtration columns from a cell wall protein fraction extracted with 1 M sodium chloride. The purified enzyme gave a single protein band of 33 kDa on SDS-PAGE. The enzyme specifically cleaved xyloglucans and showed maximum activity at pH 5.0 when assayed by the iodine-staining method. An increase in reducing power in xyloglucan solution was clearly detected after treatment with the purified enzyme. Xyloglucans with molecular masses of 500 and 25 kDa were gradually hydrolyzed to 5 kDa for 96 h without production of any oligo- or monosaccharide with the purified enzyme. The purified enzyme did not show an endo-type transglycosylation reaction, even in the presence of xyloglucan oligosaccharides. Partial amino acid sequences of the enzyme shared an identity with endo-xyloglucan transferase (EXGT) family, especially with xyloglucan endotransglycosylase (XET) from nasturtium. These results suggest that the enzyme is a new member of EXGT devoted solely to xyloglucan hydrolysis.

Cell Wall↗
PubMed2001

[Usefulness of the Centrifuge Accommodation Module for analyzing gravity responses in plant seedlings].

Onboard centrifuges are indispensable tools for clarifying the effects of microgravity on various physiological processes in plant seedlings. Centrifuges are basically attached to the incubators designed for the International Space Station (ISS). However, because of the limitation in size, that loaded to the Cell Biology Experiment Facility (CBEF) is usable only to some small seedlings such as Arabidopsis. The Centrifuge Accommodation Module (CAM) has great advantages in the size and the amounts of plant materials feasible to load, the quality of acceleration produced, and the easiness of operation on it. The CAM is an apparatus that characterizes the ISS most and its construction on schedule is highly expected.

Centrifugation↗
PubMed2000

Involvement of ethylene and gibberellin signalings in chromosaponin I-induced cell division and cell elongation in the roots of Arabidopsis seedlings.

Chromosaponin I (CSI), a triterpenoid saponin isolated from pea, stimulates the growth of roots in Arabidopsis thaliana seedlings on wetted filter paper in the light for 14 d. The growth rates of roots in Columbia (Col) and Landsberg erecta (Ler) wild-types were 0.92 and 0.26 mm d(-1), respectively, and they were accelerated to 3.46 (Col) and 2.20 (Ler) mm d(-1) by treating with 300 microM CSI. The length of mature epidermal cells was increased by 1.8-fold (Col) and 2.81-fold (Ler) compared with control and the number of epidermal cells was increased by a factor of 1.65 (Col) and 2.12 (Ler). Treatment with 2-aminoethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis, also increased cell length but not cell number. The effects of CSI on root growth were not detected in the ethylene-insensitive mutant ein2-1. CSI did not inhibit ethylene production but stimulated the growth of roots in ctr1-1, the constitutive triple response mutant for ethylene, indicating that CSI inhibits ethylene signaling, especially downstream of CTR1. In the GA-insensitive mutant gai and the mutant spy-3, in which the basal level of GA signaling is activated, CSI did not increase cell number, although both CSI and AVG stimulated cell elongation in these mutants. These results suggest that the inhibition of ethylene signaling is the cause of CSI-induced cell elongation. A possible involvement of both GA and ethylene signalings is discussed for the CSI-induced cell division.

Aminobutyrates↗
PubMed2000

Changes in the apoplastic pH are involved in regulation of xyloglucan breakdown of azuki bean epicotyls under hypergravity conditions.

Hypergravity inhibited elongation growth of azuki bean (Vigna angularis Ohwi et Ohashi) epicotyls by decreasing the mechanical extensibility of cell walls via the increase in the molecular mass of xyloglucans [Soga et al. (1999) Plant Cell Physiol. 40: 581]. Here, we report that the pH value of the apoplastic fluid in epicotyls increased from 5.8 to 6.6 by hypergravity (300 x g) treatment. When the xyloglucan-degrading enzymes extracted from cell walls of the 1 x g control epicotyls were assayed in buffer at pH 6.6 and 5.8, the activity at pH 6.6 was almost half of that at pH 5.8. In addition, when enzymically active cell wall preparations obtained from 1 x g control epicotyls were autolyzed in buffer at pH 5.8 and 6.6 and then xyloglucans were extracted from the autolyzed cell walls, the molecular mass of xyloglucans incubated at pH 5.8 decreased during the autolysis, while that at pH 6.6 did not change. Thus, the xyloglucans were not depolymerized by autolysis at the pH value (6.6) observed in the hypergravity-treated epicotyls. These findings suggest that in azuki bean epicotyls, hypergravity decreases the activities of xyloglucan-degrading enzymes by increasing the pH in the apoplastic fluid, which may be involved in the processes of the increase in the molecular mass of xyloglucans, leading to the decrease in the cell wall extensibility.

Biomechanical Phenomena↗
PubMed2000

Flower stalk segments of Arabidopsis thaliana ecotype Columbia lack the capacity to grow in response to exogenously applied auxin.

Exogenously applied IAA stimulated cell elongation of segments excised from flower stalks of Arabidopsis thaliana ecotype Landsberg erecta (Ler) by increasing the cell wall extensibility, but it did not affect that of ecotype Columbia (Col). Treatment with a low pH buffer solution (pH 4.0) or fusicoccin (FC), a reagent activating H(+)-ATPases, significantly increased the cell wall extensibility and promoted elongation growth of flower stalk segments of both ecotypes, indicating that the flower stalk segments of Col possess the capacity to grow under acidic pH conditions. IAA promoted the proton excretion in segments of Ler but not of Col. On the other hand, FC increased the proton excretion in segments of Col as much as that of Ler. These results suggest that IAA activates the plasma membrane H(+)-ATPases in the segments of Ler but not those of Col, while FC activates them in both ecotypes. Flower stalks of Col may lack the mechanisms of activation by IAA of the plasma membrane H(+)-ATPases.

Arabidopsis↗
PubMed2000

Growth regulation mechanisms in higher plants under microgravity conditions - changes in cell wall metabolism.

During Space Shuttle STS-95 mission, we cultivated seedlings of rice (Oryza sativa L. cv. Koshihikari and cv. Tan-ginbozu) and Arabidopsis (Arabidopsis thaliana L. cv. Columbia and cv. etr1-1) for 68.5, 91.5, and 136 hr on board, and then analyzed changes in the nature of their cell walls, growth, and morphogenesis under microgravity conditions. In space, elongation growth of both rice coleoptiles and Arabidopsis hypocotyls was stimulated. Also, the increase in the cell wall extensibility, especially that in the irreversible extensibility, was observed for such materials. The analyses of the amounts, the structure, and the physicochemical properties of the cell wall constituents indicated that the decreases in levels and molecular masses of cell wall polysaccharides were induced under microgravity conditions, which appeared to contribute to the increase in the wall extensibility. The activity of certain wall enzymes responsible for the metabolic turnover of the wall polysaccharides was increased in space. By the space flight, we also confirmed the occurrence of automorphogenesis of both seedlings under microgravity conditions; rice coleoptiles showed an adaxial bending, whereas Arabidopsis hypocotyls elongated in random directions. Furthermore, it was shown that spontaneous curvatures of rice coleoptiles in space were brought about uneven modifications of cell wall properties between the convex and the concave sides.

Arabidopsis↗
PubMed2000

Suitable experimental design for determination of auxin polar transport in space using a spacecraft.

It is necessary to establish a suitable experimental design for the determination of auxin (indole-3-acetic acid: IAA) polar transport in space using a spacecraft in concerning with the role of gravity. Problems in space experiments are as follows: I) Selection of suitable plant species; II) Preservation of integrity of plant segments for activities of auxin polar transport; III) Stop of auxin polar transport of the segments after the transport experiment in space. Segments of etiolated pea epicotyls and etiolated maize coleoptiles showed relatively high activities of auxin polar transport among dicotyledonous and monocotyledonous plants tested, respectively. The activities decreased dramatically when the segments were pre-stored at 25 degrees C only for 1 day. On the other hand, the storage at low temperature (5 degrees C) in the presence of antioxidants or chelating agents, especially EGTA, maintained relatively high activities of auxin polar transport in pea epicotyl segments. Low temperature (5 degrees C) substantially inhibited the activity of auxin polar transport. Based on the results in this study, a suitable experimental design for the space experiment of auxin polar transport using a spacecraft is also proposed.

Biological Transport↗
PubMed2000

Hypergravity-induced increase in the apoplastic pH and its possible involvement in suppression of beta-glucan breakdown in maize seedlings.

Elongation growth of both coleoptiles and mesocotyls of maize (Zea mays L. cv. Cross Bantam T51) seedlings was inhibited under basipetal hypergravity (300 g) conditions. Hypergravity increased the pH of the apoplastic fluid of coleoptiles from 5.0 to 5.5 and mesocotyls from 5.2 to 5.7. When beta-1,3:1,4-D-glucanases (beta-glucanases) extracted from cell walls of the 1-g control coleoptiles and mesocotyls were assayed at pH 5.0 and 5.5 for coleoptiles, and at 5.2 and 5.7 for mesocotyls, respectively, the activity in the increased pH conditions was significantly lower than that in the control pH conditions. During the autolysis of the enzymically active cell wall preparations obtained from 1-g control organs, a molecular mass downshift of hemicellulosic polysaccharides occurred in cell walls. This downshift was suppressed in the increased pH conditions as compared with the control pH conditions. It was reported that hypergravity increased the molecular mass of hemicellulosic polysaccharides by decreasing the beta-glucanase activity, and thereby decreased the mechanical extensibility of cell walls in maize coleoptiles and mesocotyls. These results suggest that, in maize coleoptiles and mesocotyls, hypergravity-induced increase in the pH in the apoplastic fluid is involved in the reduction of the activity of beta-glucanases which, in turn, causes an increase in the molecular mass of hemicellulosic polysaccharides and inhibits elongation growth.

Cell Wall↗