The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Marcel Quint - One of the best experts on this subject based on the ideXlab platform.
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a mobile auxin signal connects temperature sensing in cotyledons with growth responses in Hypocotyls
Plant Physiology, 2019Co-Authors: Julia Bellstaedt, Jana Trenner, Rebecca Lippmann, Yvonne Poeschl, Xixi Zhang, Jiri Friml, Marcel QuintAbstract:Plants have a remarkable capacity to adjust their growth and development to elevated ambient temperatures. Increased elongation growth of roots, Hypocotyls, and petioles in warm temperatures are hallmarks of seedling thermomorphogenesis. In the last decade, significant progress has been made to identify the molecular signaling components regulating these growth responses. Increased ambient temperature utilizes diverse components of the light sensing and signal transduction network to trigger growth adjustments. However, it remains unknown whether temperature sensing and responses are universal processes that occur uniformly in all plant organs. Alternatively, temperature sensing may be confined to specific tissues or organs, which would require a systemic signal that mediates responses in distal parts of the plant. Here, we show that Arabidopsis (Arabidopsis thaliana) seedlings show organ-specific transcriptome responses to elevated temperatures and that thermomorphogenesis involves both autonomous and organ-interdependent temperature sensing and signaling. Seedling roots can sense and respond to temperature in a shoot-independent manner, whereas shoot temperature responses require both local and systemic processes. The induction of cell elongation in Hypocotyls requires temperature sensing in cotyledons, followed by the generation of a mobile auxin signal. Subsequently, auxin travels to the hypocotyl, where it triggers local brassinosteroid-induced cell elongation in seedling stems, which depends upon a distinct, permissive temperature sensor in the hypocotyl.
U. Kutschera - One of the best experts on this subject based on the ideXlab platform.
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Sucrose metabolism and cellulose biosynthesis in sunflower Hypocotyls.
Physiologia Plantarum, 2002Co-Authors: U. Kutschera, A. HeiderichAbstract:The relationships between cellulose accumulation, changes in specific activities of enzymes of sucrose catabolism, levels of UDP-glucose and rate of dark respiration were investigated in the subapical 1 cm-hypocotyl region of 10- to 14-day-old-sunflower seedlings (Helianthus annuus L). The plants were grown under a light/dark regime in vermiculite that was soaked either with distilled water or half-strength Hoagland nutrient solution. At this stage of seedling development, the hypocotyl had ceased to elongate but increased in width. Stem thickening and the rate of cellulose accumulation were promoted by nutrient solution. The levels of the soluble (vacuolar) and wall-associated acid invertases (EC 3.2.1.26) were not correlated with these processes. However, the activities of the soluble (cytoplasmic) and membrane-bound sucrose synthases (EC 2.4.1.13) were larger in Hypocotyls that were grown in the presence of nutrient solution. The concentration of UDP-glucose was reduced, and the rate of dark respiration was enhanced in the Hypocotyls that were grown in Hoagland solution. The results support the hypothesis that both forms of the enzyme sucrose synthase play a critical role in cellulose biosynthesis of hypocotyl cells that had ceased to elongate and continue to grow by wall thickening.
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Effect of white light on meristematic activity in developing sunflower Hypocotyls
Protoplasma, 1996Co-Authors: T. Heupel, U. KutscheraAbstract:To determine whether hypocotyl elongation in sunflower seedlings ( Helianthus annuus L.) is dependent on cell divisions (meristematic activity), we used a specific inhibitor of DNA synthesis (fluorodeoxyuridine). The seedlings were either grown for 6 days in darkness or continuous white light (WL). Under both conditions hypocotyl growth was retarded by 30–70% in the presence of the inhibitor. Because the nuclei do not become endopolyploid we conclude that hypocotyl growth is dependent on cell reproduction. In the next step an immunocytochemical method was used to detect the percentage of nuclei in S-phase (meristematic activity) in different regions and tissues of the Hypocotyls. In the peripheral cell layers (epidermis, cortex) meristematic activity was much greater than in the pith of the organ. In rapidly growing (etiolated) Hypocotyls meristematic activity is largely restricted to the closed apical hook of the stem. After transfer to WL the hook opens and hypocotyl elongation is inhibited. In the epidermis and cortex of the apical hook a large WL-induced enhancement in the percentage of nuclei in S-phase occurred, which was followed by a light-mediated retardation of meristematic activity. Our data show that WL exerts a transient stimulatory effect on meristematic activity during photomorphogenesis of the sunflower seedling.
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cell wall synthesis and elongation growth in Hypocotyls of helianthus annuus l
Planta, 1990Co-Authors: U. KutscheraAbstract:The relationship between growth and increase in cell-wall material (wall synthesis) was investigated in Hypocotyls of sunflower seedlings (Helianthus annuus L.) that were either grown in the dark or irradiated with continuous white light (WL). The peripheral three to four cell layers comprised 30–50% of the entire wall material of the hypocotyl. The increase in wall material during growth in the dark and WL, respectively, was larger in the inner tissues than in the peripheral cell layers. The wall mass per length decreased continuously, indicating that wall thinning occurs during growth of the hypocotyl. When dark-grown seedlings were transfered to WL, a 70% inhibition of growth was observed, but the increase in wall mass was unaffected. Likewise, the composition of the cell walls (cellulose, hemicellulose, pectic substances) was not affected by WL irradiation. Upon transfer of dark-grown seedlings into WL a drastic increase in wall thickness and a concomitant decrease in cell-wall plasticity was measured. The results indicate that cell-wall synthesis and cell elongation are independent processes and that, as a result, WL irradiation of etiolated Hypocotyls leads to a thickening and mechanical stiffening of the cell walls.
Takayuki Hoson - One of the best experts on this subject based on the ideXlab platform.
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stimulation of elongation growth and xyloglucan breakdown in arabidopsis Hypocotyls under microgravity conditions in space
Planta, 2002Co-Authors: Kouichi Soga, Kazuyuki Wakabayashi, Seiichiro Kamisaka, Takayuki HosonAbstract:Seedlings of Arabidopsis thaliana (L.) Heynh. (ecotype Columbia and an ethylene-resistant mutant etr1-1) were cultivated for 68.5, 91.5 and 136 h on board during the Space Shuttle STS-95 mission, and changes in the elongation growth and the cell wall properties of Hypocotyls were analyzed. Elongation growth of dark-grown Hypocotyls of both Columbia and etr1-1 was stimulated under microgravity conditions in space. There were no clear differences in the degree of growth stimulation between Columbia and etr1-1, indicating that the ethylene level was not abnormally high in the cultural environment of this space experiment. Microgravity also increased the mechanical extensibility of cell walls in both cultivars, and such an increase was attributed to the increase in the apparent irreversible extensibility. The levels of cell wall polysaccharides per unit length of Hypocotyls decreased in space. Microgravity also reduced the weight-average molecular mass of xyloglucans in the hemicellulose-II fraction. Also, the activity of xyloglucan-degrading enzymes extracted from hypocotyl cell walls increased under microgravity conditions. These results suggest that microgravity reduces the molecular mass of xyloglucans by increasing xyloglucan-degrading activity. Modifications of xyloglucan metabolism as well as the thickness of cell wall polysaccharides seem to be involved in an increase in the cell wall extensibility, leading to growth stimulation of Arabidopsis Hypocotyls in space.
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gravitational force regulates elongation growth of arabidopsis Hypocotyls by modifying xyloglucan metabolism
Advances in Space Research, 2001Co-Authors: Kouichi Soga, Kazuyuki Wakabayashi, Takayuki Hoson, Seiichiro KamisakaAbstract:Abstract 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.
Julia Bellstaedt - One of the best experts on this subject based on the ideXlab platform.
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a mobile auxin signal connects temperature sensing in cotyledons with growth responses in Hypocotyls
Plant Physiology, 2019Co-Authors: Julia Bellstaedt, Jana Trenner, Rebecca Lippmann, Yvonne Poeschl, Xixi Zhang, Jiri Friml, Marcel QuintAbstract:Plants have a remarkable capacity to adjust their growth and development to elevated ambient temperatures. Increased elongation growth of roots, Hypocotyls, and petioles in warm temperatures are hallmarks of seedling thermomorphogenesis. In the last decade, significant progress has been made to identify the molecular signaling components regulating these growth responses. Increased ambient temperature utilizes diverse components of the light sensing and signal transduction network to trigger growth adjustments. However, it remains unknown whether temperature sensing and responses are universal processes that occur uniformly in all plant organs. Alternatively, temperature sensing may be confined to specific tissues or organs, which would require a systemic signal that mediates responses in distal parts of the plant. Here, we show that Arabidopsis (Arabidopsis thaliana) seedlings show organ-specific transcriptome responses to elevated temperatures and that thermomorphogenesis involves both autonomous and organ-interdependent temperature sensing and signaling. Seedling roots can sense and respond to temperature in a shoot-independent manner, whereas shoot temperature responses require both local and systemic processes. The induction of cell elongation in Hypocotyls requires temperature sensing in cotyledons, followed by the generation of a mobile auxin signal. Subsequently, auxin travels to the hypocotyl, where it triggers local brassinosteroid-induced cell elongation in seedling stems, which depends upon a distinct, permissive temperature sensor in the hypocotyl.
Kotaro T Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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space time analysis of gravitropism in etiolated arabidopsis Hypocotyls using bioluminescence imaging of the iaa19 promoter fusion with a destabilized luciferase reporter
Journal of Plant Research, 2017Co-Authors: Kotaro T Yamamoto, Masaaki K Watahiki, Jun Matsuzaki, Soichirou Satoh, Hisayo ShimizuAbstract:Imaging analysis was carried out during the gravitropic response of etiolated Arabidopsis Hypocotyls, using an IAA19 promoter fusion of destabilized luciferase as a probe. From the bright-field images we obtained the local deflection angle to the vertical, A, local curvature, C, and the partial derivative of C with respect to time, $$\partial C/\partial t$$ . These were determined every 19.9 µm along the curvilinear length of the hypocotyl, at ~10 min intervals over a period of ~6 h after turning Hypocotyls through 90° to the horizontal. Similarly from the luminescence images we measured the luminescence intensity of the convex and concave flanks of the hypocotyl as well as along the median of the hypocotyl, to determine differential expression of auxin-inducible IAA19. Comparison of these parameters as a function of time and curvilinear length shows that the gravitropic response is composed of three successive elements: the first and second curving responses and a decurving response (autostraightening). The maximum of the first curving response occurs when A is 76° along the entire length of the hypocotyl, suggesting that A is the sole determinant in this response; in contrast, the decurving response is a function of both A and C, as predicted by the newly-proposed graviproprioception model (Bastien et al., Proc Natl Acad Sci USA 110:755–760, 2013). Further, differential expression of IAA19, with higher expression in the convex flank, is observed at A = 44°, and follows the Sachs’ sine law. This also suggests that IAA19 is not involved in the first curving response. In summary, the gravitropic response of Arabidopsis Hypocotyls consists of multiple elements that are each determined by separate principles.
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inhibition of brassinosteroid biosynthesis by either a dwarf4 mutation or a brassinosteroid biosynthesis inhibitor rescues defects in tropic responses of Hypocotyls in the arabidopsis mutant nonphototropic hypocotyl 4
Plant Physiology, 2006Co-Authors: Daisuke Nakamoto, Tadao Asami, Akimitsu Ikeura, Kotaro T YamamotoAbstract:The nonphototropic hypocotyl 4 (nph4)/auxin response factor 7 (arf7) mutant of Arabidopsis (Arabidopsis thaliana) is insensitive to auxin and has defects in hypocotyl tropism, hook formation, differential leaf growth, and lateral root formation. To understand an auxin-signaling pathway through NPH4, we carried out screening of suppressor mutants of nph4-103 and obtained a dwarf suppressor mutant, suppressor of nph4 (snp2). snp2 had short Hypocotyls in the dark condition and dark green and round leaves, short petioles, and more lateral shoots than the wild type in the light condition. The snp2 phenotypes were rescued by adding brassinolide to the growth medium in both light and dark conditions. Genetic mapping, sequence analysis, and a complementation test indicated that snp2 was a weak allele of DWARF4 (DWF4), which functions in brassinosteroid (BR) biosynthesis. snp2, which was renamed dwf4-101, exhibited photo- and gravitropisms of Hypocotyls similar to those of the wild type with a slightly faster response in gravitropism. dwf4-101 almost completely suppressed defects in both tropisms of nph4-103 Hypocotyls and completely suppressed hyponastic growth of nph4-103 leaves. Treatment with brassinazole, an inhibitor of BR biosynthesis, also partially rescued the tropic defects in nph4-103. Hypocotyls of nph4-103 were auxin insensitive, whereas Hypocotyls of dwf4-101 were more sensitive than those of the wild type. dwf4-101 nph4-103 Hypocotyls were as sensitive as those of dwf4-101. Auxin inducibility of massugu 2 (MSG2)/IAA19 gene expression was reduced in nph4-103. mRNA level of MSG2 was reduced in dwf4-101 and dwf4-101 nph4-103, but both mutants exhibited greater auxin inducibility of MSG2 than the wild type. Taken together, dwf4-101 was epistatic to nph4-103. These results strongly suggest that BR deficiency suppresses nph4-103 defects in tropic responses of Hypocotyls and differential growth of leaves and that BR negatively regulates tropic responses.
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massugu2 encodes aux iaa19 an auxin regulated protein that functions together with the transcriptional activator nph4 arf7 to regulate differential growth responses of hypocotyl and formation of lateral roots in arabidopsis thaliana
The Plant Cell, 2004Co-Authors: Kiyoshi Tatematsu, Emmanuel Liscum, Masaaki K Watahiki, Satoshi Kumagai, Hideki Muto, Atsuko Sato, Renee M Harper, Kotaro T YamamotoAbstract:We have isolated a dominant, auxin-insensitive mutant of Arabidopsis thaliana, massugu2 (msg2), that displays neither hypocotyl gravitropism nor phototropism, fails to maintain an apical hook as an etiolated seedling, and is defective in lateral root formation. Yet other aspects of growth and development of msg2 plants are almost normal. These characteristics of msg2 are similar to those of another auxin-insensitive mutant, non-phototropic hypocotyl4 (nph4), which is a loss-of-function mutant of AUXIN RESPONSE FACTOR7 (ARF7) (Harper et al., 2000). Map-based cloning of the MSG2 locus reveals that all four mutant alleles result in amino acid substitutions in the conserved domain II of an Auxin/Indole-3-Acetic Acid protein, IAA19. Interestingly, auxin inducibility of MSG2/IAA19 gene expression is reduced by 65% in nph4/arf7. Moreover, MSG2/IAA19 protein binds to the C-terminal domain of NPH4/ARF7 in a Saccharomyces cerevisiae (yeast) two-hybrid assay and to the whole latter protein in vitro by pull-down assay. These results suggest that MSG2/IAA19 and NPH4/ARF7 may constitute a negative feedback loop to regulate differential growth responses of Hypocotyls and lateral root formation.
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The massugu1 Mutation of Arabidopsis Identified with Failure of Auxin-Induced Growth Curvature of Hypocotyl Confers Auxin Insensitivity to Hypocotyl and Leaf
Plant Physiology, 1997Co-Authors: Masaaki K Watahiki, Kotaro T YamamotoAbstract:Unilateral application of indole-3-acetic acid (IAA) in a lanolin base to Hypocotyls of partially etiolated seedlings of wild-type Arabidopsis thaliana induced growth curvature in a dose-dependent manner. The effects of IAA in concentrations from 1 to 1000 [mu]M were studied, with maximum IAA-induced curvature at 100 [mu]M. Three IAA-insensitive mutants were isolated and are all in the same locus, massugu1 (msg1). They did not undergo hypocotyl growth curvature at any of the IAA concentrations tested. msg1 is recessive and is located on chromosome 5. msg1 hypocotyl growth is resistant to 2,4-dichlorophenoxyacetic acid (2,4-D), but the roots are as sensitive to 2,4-D as the wild type. Growth of the hypocotyl was inhibited to essentially the same extent as the wild type by 6-benzylaminopurine, abscisic acid, and l-aminocyclopropane-1-carboxylate, an ethylene precursor. The msg1 leaves were also resistant to 2,4-D-induced chlorosis. The gravitropic response of the msg1 hypocotyl takes much more time to initiate and achieve the wild-type degree of curvature, whereas the msg1 roots responded normally to gravity. The mature plants and the etiolated seedlings of msg1 were generally wild type in appearance, except that their rosette leaves were either epinastic or hyponastic. msg1 is the first auxin-insensitive mutant in which its effects are mostly restricted to the hypocotyl and leaf, and msg1 also appears to be auxin specific.
