Página 1 dos resultados de 1180 itens digitais encontrados em 0.004 segundos

Controle do desenvolvimento vegetal pela interação auxina-citocinina. Uma nova abordagem baseada no estudo de mutantes de tomateiro (Solanun lycopersicum cv Micro-Tom); Control of plant development by auxin-cytokinin interactions. A new approach based on tomato (Solanum lycopersicum cv Micro-Tom) mutants.

Pino-Nunes, Lilian Ellen
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/06/2009 PT
Relevância na Pesquisa
37.5%
Os hormônios auxina e citocininas são essenciais ao desenvolvimento das plantas, pois controlam os processos de divisão, expansão e diferenciação celular, os quais, por sua vez, influenciam desde a formação do embrião até o amadurecimento dos frutos e senescência. Auxinas e citocininas regulam respostas fisiológicas comuns, sugerindo haver múltiplos mecanismos de interação. Neste trabalho, um modelo para estudar a interação entre auxinas e citocininas no controle do desenvolvimento é proposto, sendo baseado em plantas mutantes e transgênicas, além de duplos mutantes, com alterações na sensibilidade ou metabolismo de auxina e citocinina. O mutante bushy root (brt) foi caracterizado como pouco sensível à citocinina e sugere uma importante função da citocinina no desenvolvimento da semente e na determinação da dominância apical em tomateiro. Os mutantes potato leaf (c) e entire (e) foram introgredidos no background Micro-Tom (MT), caracterizados e utilizados para verificar como eles afetam a sensibilidade à auxina e como interferem no desenvolvimento da planta. Esses mutantes foram comparados com MT, com o mutante diageotropica (dgt), que é pouco sensível à auxina, e com os duplos mutantes c dgt e dgt e. A mutação c não alterou a sensibilidade à auxina e estaria influenciando apenas a arquitetura foliar. O mutante e parece ser mais sensível à auxina com relação à capacidade de formar raízes in vitro e partenocarpia. O duplo mutante dgt e mostrou fenótipo aditivo (intermediário)...

Characterization and expression of cytokinin signalling genes in sulfur deficient grapevine (Vitis vinifera L.)

Fernandes, João Carlos Martins
Fonte: Universidade Técnica de Lisboa Publicador: Universidade Técnica de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2009 ENG
Relevância na Pesquisa
37.31%
Mestrado em Engenharia Agronómica - Instituto Superior de Agronomia; Sulfur (S) is an essential macronutrient for plant growth and development. In vitro grapevine callus, cells and shoots in culture media in the absence of sulfur (-S) respond markedly with a reduction of growth and shoot multiplication. This may result from an interference of -S with cytokinin signal pathway (CSP) or at shoot apical meristem (SAM) or axillary meristem (AM) identity level. Cytokinins are essential plant hormones that control various processes in plants. As in Arabidopsis, Vitis CSP is composed by receptors (HKs), phosphotransmitters (HPTs) and two types of response regulators (A-type and B-type RRs). Cells in -S in the presence of cytokinin show a downregulation of most CSP genes while -S without cytokinin leads to an upregulation of A-type RRs. CSP is not significantly affected by –S in in vitro shoots, so the multiplication inhibition can be caused by a downregulation of the expression of SAM and AM identity genes, respectively STM and LAS. In vitro conditions more similar to autotrophy as Temporary Immersion System, the scarce multiplication impairment must result from the reduction of B-type RRs transcription. As a whole the present work provides new insights on the crosstalk between –S and cytokinin signaling in in vitro grapevine model systems.

Cytokinin Dehydrogenase activity in primary roots and characterization of primary metabolites from leaves and rootlets of Ricinus Communis

Marques,Maria Elizabeth da Costa; Freitas,Beatriz Tupinambá; Guedes,Tarciana Oliveira; Fernandes,Roberta Pereira Miranda
Fonte: Instituto de Tecnologia do Paraná - Tecpar Publicador: Instituto de Tecnologia do Paraná - Tecpar
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2013 EN
Relevância na Pesquisa
36.98%
The aim of this study was to determine the activity of cytokinin dehydrogenase (CKX) and to measure other biochemical components in the primary leaves and radicles of castor seedlings (BRS Energia) in the initial phase of growth. The crude protein extract obtained after a 1-h extraction from the root tissues of seedlings showed no detectable CKX enzymatic activity when incubated with the substrate isopentenyl adenine for 1 h. However, after precipitation with ammonium sulfate at 70% saturation, the pellet showed CKX activity. The peroxidase enzyme activity was higher in the leaves than in the radicles. The total and reducing sugar content was 1.5 times higher in the leaves than in the radicles. The amino acid and protein contents were 6.4 and 9.2 times higher in the leaves than in the radicles, respectively.

The Diageotropica Gene Differentially Affects Auxin and Cytokinin Responses throughout Development in Tomato1

Coenen, Catharina; Lomax, Terri L.
Fonte: American Society of Plant Physiologists Publicador: American Society of Plant Physiologists
Tipo: Artigo de Revista Científica
Publicado em /05/1998 EN
Relevância na Pesquisa
27.58%
The interactions between the plant hormones auxin and cytokinin throughout plant development are complex, and genetic investigations of the interdependency of auxin and cytokinin signaling have been limited. We have characterized the cytokinin sensitivity of the auxin-resistant diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) in a range of auxin- and cytokinin-regulated responses. Intact, etiolated dgt seedlings showed cross-resistance to cytokinin with respect to root elongation, but cytokinin effects on hypocotyl growth and ethylene synthesis in these seedlings were not impaired by the dgt mutation. Seven-week-old, green wild-type and dgt plants were also equally sensitive to cytokinin with respect to shoot growth and hypocotyl and internode elongation. The effects of cytokinin and the dgt mutation on these processes appeared additive. In tissue culture organ regeneration from dgt hypocotyl explants showed reduced sensitivity to auxin but normal sensitivity to cytokinin, and the effects of cytokinin and the mutation were again additive. However, although callus induction from dgt hypocotyl explants required auxin and cytokinin, dgt calli did not show the typical concentration-dependent stimulation of growth by either auxin or cytokinin observed in wild-type calli. Cross-resistance of the dgt mutant to cytokinin thus was found to be limited to a small subset of auxin- and cytokinin-regulated growth processes affected by the dgt mutation...

The Effects of Cytokinin and Light on Hypocotyl Elongation in Arabidopsis Seedlings Are Independent and Additive.

Su, W.; Howell, S. H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1995 EN
Relevância na Pesquisa
27.58%
Cytokinin has been reported to mimic some of the effects of light on de-etiolation responses in dark-grown Arabidopsis seedlings. The interaction between cytokinin and light was examined by analyzing cytokinin dose and light fluence effects on hypocotyl elongation in wild-type and mutant Arabidopsis seedlings with defects in light or hormone responses. It was found that (a) cytokinin and light-response systems have independent and additive effects on the inhibition of hypocotyl elongation and (b) either cytokinin or light can saturate the morphogenic responses. As a consequence, cytokinin has no effect on hypocotyl elongation under normal growth conditions because light levels saturate the hypocotyl inhibition response. To determine whether a functional light-response pathway is required for cytokinin responses, light-insensitive long hypocotyl (hy) mutants were tested for cytokinin responses. The hy mutants (hy1 to hy6) had normal cytokinin responses, except phyB-1 (hy3-1), in which hypocotyl elongation was insensitive to cytokinin. Cytokinin insensitivity in phyB-1 was attributed to an indirect effect of the mutation on cytokinin responses. The effects of cytokinin on the inhibition of hypocotyl elongation are largely mediated by ethylene...

Cell-autonomous cytokinin-independent growth of tobacco cells transformed by Agrobacterium tumefaciens strains lacking the cytokinin biosynthesis gene.

Black, R C; Binns, A N; Chang, C F; Lynn, D G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1994 EN
Relevância na Pesquisa
27.52%
Mutations at the cytokinin biosynthesis locus (tmr) of Agrobacterium tumefaciens usually result in strains that induce tumors exhibiting the rooty phenotype associated with high auxin-to-cytokinin ratios. However, tobacco (Nicotiana tabacum cv Havana 425) leaf disc explants responded to tmr- mutant strain A356 by producing rapidly growing, unorganized tumors, indicating that these lines can grow in a cytokinin-independent fashion despite the absence of a functional tmr gene. Several methods have been used to characterize the physiological and cellular basis of this phenotype. The results indicate that tmr- tumors have a physiologically distinct mechanism for cytokinin-independent growth in comparison to tumors induced by wild-type bacteria. The cytokinin-independent phenotype of the tmr- transformants appears to be cell autonomous in nature: only the transformed cells and their progeny were capable of cytokinin-independent growth. Specifically, the tmr- tumors did not accumulate cytokinin, and clonal analysis indicated the tmr- transformed cells were not capable of stimulating the growth of neighboring nontransformed cells. Finally, the cytokinin-independent phenotype of the tmr- transformants was shown to be cold sensitive, whereas the wild-type tumors exhibited a cold-resistant cytokinin-independent phenotype. Potential mechanisms for this novel form of cytokinin-independent growth...

Expression Profiling of Cytokinin Action in Arabidopsis1[w]

Rashotte, Aaron M.; Carson, Susan D.B.; To, Jennifer P.C.; Kieber, Joseph J.
Fonte: The American Society for Plant Biologists Publicador: The American Society for Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /08/2003 EN
Relevância na Pesquisa
27.55%
The phytohormone cytokinin is an important regulator of plant growth and development; however, relatively few genes that mediate cytokinin responses have been identified. Genome-wide analyses of Arabidopsis seedlings using the approximately 8,300-element Affymetrix Arabidopsis GeneChips (Affymetrix, Santa Clara, CA) to examine cytokinin-responsive genes were conducted, revealing at least 30 genes whose steady-state level of mRNA was elevated and at least 40 that were down-regulated at multiple time points after application of cytokinin. The cytokinin up-regulated genes include the type-A Arabidopsis response regulators (ARRs), which had been shown previously to be cytokinin primary response genes, cytokinin oxidase, which encodes an enzyme that degrades cytokinins, and several transcription factors. Cytokinin down-regulated genes include several peroxidases and kinases and an E3 ubiquitin ligase. We identified a common sequence motif enriched in the upstream regions of the most consistently cytokinin up-regulated genes. This motif is highly similar to the optimal DNA-binding sites for ARR1/ARR2, type-B ARRs that have been implicated in the transcriptional elevation of the type-A ARRs. Additionally, genome-wide analyses of cytokinin receptor mutants (wol/cre1) revealed large-scale changes in gene expression...

Cross Talk between Gibberellin and Cytokinin: The Arabidopsis GA Response Inhibitor SPINDLY Plays a Positive Role in Cytokinin Signaling

Greenboim-Wainberg, Yaarit; Maymon, Inbar; Borochov, Roy; Alvarez, John; Olszewski, Neil; Ori, Naomi; Eshed, Yuval; Weiss, David
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /01/2005 EN
Relevância na Pesquisa
27.54%
SPINDLY (SPY) is a negative regulator of gibberellin (GA) responses; however, spy mutants exhibit various phenotypic alterations not found in GA-treated plants. Assaying for additional roles for SPY revealed that spy mutants are resistant to exogenously applied cytokinin. GA also repressed the effects of cytokinin, suggesting that there is cross talk between the two hormone-response pathways, which may involve SPY function. Two spy alleles showing severe (spy-4) and mild (spy-3) GA-associated phenotypes exhibited similar resistance to cytokinin, suggesting that SPY enhances cytokinin responses and inhibits GA signaling through distinct mechanisms. GA and spy repressed numerous cytokinin responses, from seedling development to senescence, indicating that cross talk occurs early in the cytokinin-signaling pathway. Because GA3 and spy-4 inhibited induction of the cytokinin primary-response gene, type-A Arabidopsis response regulator 5, SPY may interact with and modify elements from the phosphorelay cascade of the cytokinin signal transduction pathway. Cytokinin, on the other hand, had no effect on GA biosynthesis or responses. Our results demonstrate that SPY acts as both a repressor of GA responses and a positive regulator of cytokinin signaling. Hence...

Genotypic Variation in Cytokinin Oxidase from Phaseolus Callus Cultures 1

Kaminek, Miroslav; Armstrong, Donald J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1990 EN
Relevância na Pesquisa
27.54%
Genotypic variation in cytokinin oxidase has been detected in enzyme preparations from Phaseolus vulgaris L. cv Great Northern and Phaseolus lunatus L. cv Kingston callus cultures. Although cytokinin oxidase preparations from Great Northern and Kingston callus tissues appear to have very similar substrate specificities, the cytokinin oxidase activities from the two callus tissues were found to differ in a number of other properties. The cytokinin oxidase from P. vulgaris cv Great Northern callus tissue exhibited a pH optimum of 6.5 (bisTris) and had a strong affinity for the lectin concanavalin A. The cytokinin oxidase from P. lunatus cv Kingston callus tissue exhibited a pH optimum of 8.4 (Taps) and did not bind to concanavalin A. The two enzymes also differed in position of elution when chromatographed on DEAE-cellulose. Both cytokinin oxidase activities exhibited enhanced activity and lower pH optima in the presence of copper-imidazole complexes, but the optimum copper-imidazole ratio and the magnitude of enhancement differed for the two activities. In both callus tissues, transient increases in the supply of exogenous cytokinins induced increases in cytokinin oxidase activity. The differences in pH optima and in glycosylation (as evidenced by the observed difference in lectin affinity) of the cytokinin oxidases from Great Northern and Kingston callus tissues suggest that the compartmentation of cytokinin oxidase may differ in the two callus tissues. The possibility that enzyme compartmentation and isozyme variation in cytokinin oxidase may play a role in the regulation of cytokinin degradation in plant tissues is discussed in relation to known differences in the rates of cytokinin degradation in Great Northern and Kingston callus tissues.

Cytokinin Autonomy in Tissue Cultures of Phaseolus: A Genotype-Specific and Heritable Trait

Mok, Machteld C.; Mok, David W. S.; Armstrong, Donald J.; Rabakoarihanta, Aimée; Kim, Sang-Gu
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1980 EN
Relevância na Pesquisa
27.54%
Intra- and interspecific differences in cytokinin requirement were detected in callus cultures of Phaseolus vulgaris L. and P. lunatus L. Of the ten genotypes of P. vulgaris tested in the present study, one required cytokinin for callus growth, six exhibited some to moderate growth on cytokinin-free medium, and the remaining three grew uniformly in the absence of cytokinin. In contrast, six of the P. lunatus genotypes were strictly cytokinin-dependent, while four genotypes displayed irregular amount of callus growth on cytokinin-free medium. The genotype-specific behavior of Phaseolus callus tissues was independent of the tissue of origin and the time in culture. The inheritance of the cytokinin requirement of Phaseolus tissue cultures was studied in hybrid tissues resulting from crosses between a strictly cytokinin-dependent genotype (P.I. 200960) and two independent genotypes (cv. G 50 and P.I. 286303) of P. vulgaris. Fresh weights of hybrid tissues on cytokinin-free medium were intermediate between and significantly different from the parental tissues. No differences were found between reciprocal hybrids. These results suggest that cytokinin autonomy in tissue cultures of P. vulgaris is a genetic trait under nuclear control. Both parental and intermediate phenotypes were recovered in the F2 progeny. The frequency distribution of cytokinin-dependent progeny in F2 and backcross populations indicates that the cytokinin requirement of P. vulgaris callus tissue may be regulated by one set of alleles.

A subset of Arabidopsis AP2 transcription factors mediates cytokinin responses in concert with a two-component pathway

Rashotte, Aaron M.; Mason, Michael G.; Hutchison, Claire E.; Ferreira, Fernando J.; Schaller, G. Eric; Kieber, Joseph J.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.54%
The plant hormone cytokinin regulates numerous growth and developmental processes. A signal transduction pathway for cytokinin has been elucidated that is similar to bacterial two-component phosphorelays. In Arabidopsis, this pathway is comprised of receptors that are similar to sensor histidine kinases, histidine-containing phosphotransfer proteins, and response regulators (ARRs). There are two classes of response regulators, the type-A ARRs, which act as negative regulators of cytokinin responses, and the type-B ARRs, which are transcription factors that play a positive role in mediating cytokinin-regulated gene expression. Here we show that several closely related members of the Arabidopsis AP2 gene family of unknown function are transcriptionally up-regulated by cytokinin through this pathway, and we have designated these AP2 genes CYTOKININ RESPONSE FACTORS (CRFs). In addition to their transcriptional regulation by cytokinin, the CRF proteins rapidly accumulate in the nucleus in response to cytokinin, and this relocalization depends on the histidine kinases and the downstream histidine-containing phosphotransfer proteins, but is independent of the ARRs. Analysis of loss-of-function mutations reveals that the CRFs function redundantly to regulate the development of embryos...

Gene Regulation by Cytokinin in Arabidopsis

Brenner, Wolfram G.; Ramireddy, Eswar; Heyl, Alexander; Schmülling, Thomas
Fonte: Frontiers Research Foundation Publicador: Frontiers Research Foundation
Tipo: Artigo de Revista Científica
Publicado em 31/01/2012 EN
Relevância na Pesquisa
27.57%
The plant hormone cytokinin realizes at least part of its signaling output through the regulation of gene expression. A great part of the early transcriptional regulation is mediated by type-B response regulators, which are transcription factors of the MYB family. Other transcription factors, such as the cytokinin response factors of the AP2/ERF family, have also been shown to be involved in this process. Additional transcription factors mediate distinct parts of the cytokinin response through tissue- and cell-specific downstream transcriptional cascades. In Arabidopsis, only a single cytokinin response element, to which type-B response regulators bind, has been clearly proven so far, which has 5′-GAT(T/C)-3′ as a core sequence. This motif has served to construct a synthetic cytokinin-sensitive two-component system response element, which is useful for monitoring the cellular cytokinin status. Insight into the extent of transcriptional regulation has been gained by genome-wide gene expression analyses following cytokinin treatment and from plants having an altered cytokinin content or signaling. This review presents a meta analysis of such microarray data resulting in a core list of cytokinin response genes. Genes encoding type-A response regulators displayed the most stable response to cytokinin...

Transcriptome Analysis of Cytokinin Response in Tomato Leaves

Shi, Xiuling; Gupta, Sarika; Lindquist, Ingrid E.; Cameron, Connor T.; Mudge, Joann; Rashotte, Aaron M.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 25/01/2013 EN
Relevância na Pesquisa
27.55%
Tomato is one of the most economically and agriculturally important Solanaceous species and vegetable crops, serving as a model for examination of fruit biology and compound leaf development. Cytokinin is a plant hormone linked to the control of leaf development and is known to regulate a wide range of genes including many transcription factors. Currently there is little known of the leaf transcriptome in tomato and how it might be regulated by cytokinin. We employ high throughput mRNA sequencing technology and bioinformatic methodologies to robustly analyze cytokinin regulated tomato leaf transcriptomes. Leaf samples of two ages, 13d and 35d were treated with cytokinin or the solvent vehicle control dimethyl sulfoxide (DMSO) for 2 h or 24 h, after which RNA was extracted for sequencing. To confirm the accuracy of RNA sequencing results, we performed qPCR analysis of select transcripts identified as cytokinin regulated by the RNA sequencing approach. The resulting data provide the first hormone transcriptome analysis of leaves in tomato. Specifically we identified several previously untested tomato orthologs of cytokinin-related genes as well as numerous novel cytokinin-regulated transcripts in tomato leaves. Principal component analysis of the data indicates that length of cytokinin treatment and plant age are the major factors responsible for changes in transcripts observed in this study. Two hour cytokinin treatment showed a more robust transcript response indicated by both greater fold change of induced transcripts and the induction of twice as many cytokinin-related genes involved in signaling...

In vitro multiplication of 'Flordaguard' rootstock: cytokinin source and concentration effects, explants orientation and period of permanence in the culture medium

Radmann,Elizete Beatriz; Bianchi,Valmor João; Fachinello,José Carlos; Ferreira,Letícia Vanni; Oliveira,Roberto Pedroso de
Fonte: Instituto de Tecnologia do Paraná - Tecpar Publicador: Instituto de Tecnologia do Paraná - Tecpar
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2011 EN
Relevância na Pesquisa
36.98%
This work aimed at studying the effects of different sources and cytokinin concentrations, as well as explants orientation and time of their permanence in shoots induction medium to obtain high multiplication rate. Four experiments were carried out to evaluate the sprout percentage mean, shoots number per explant, elongated shoots percentage and shoots length. The treatments with 2iP and zeatin did not promote in vitro plant multiplication. When different BAP concentrations were tested, an increase in sprout percentage was obtained using BAP concentration up to 3.66 mg L-1 (80%), and for shoots number per explant a linear behavior was observed, showing a mean of four shoots per explant with 4.0 mg L-1 BAP. For the 'Flordaguard' rootstocks, the explants orientation did not alter the potential in vitro multiplication and the shoots growth. However, the explants permanence in the shoots induction medium for 40 days provided the best results for shoots growth.

Exogenous supply of glutamine and active cytokinin to the roots reduces NO3- uptake rates in poplar

Gessler, Arthur; Dluzniewska , Paulina; Kopriva, Stanislav; Strnad , Miroslav; Novak, Ondrej; Dietrich , Henriette; Rennenberg, Heinz
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.13%
The present study shows for the first time the influence of exogenously applied amino acids and cytokinin on the physiological and molecular aspects of N metabolism in poplar trees. In a short-term feeding experiment, glutamine or trans-zeatin riboside (t

Multiple roles for cytokinin receptors and cross-talk of signaling pathways

Coba de la Peña, Teodoro; Cárcamo, Claudia B.; Lucas, M. Mercedes; Pueyo, José J.
Fonte: Landes Bioscience Publicador: Landes Bioscience
Tipo: Artículo Formato: 118908 bytes; application/pdf
ENG
Relevância na Pesquisa
37.31%
4 pages.; Cytokinin receptors (CRs) are hybrid-type histidine kinases, membrane proteins with a cytokinin-binding extracellular domain. CRs initiate and propagate cytokinin signaling by means of phosphorylation and phosphotransfer to downstream proteins. In legumes, some members of the CR multigenic family are essential for nodulation. In two recent works, we investigated the involvement of two new CRs, MsHK1 from Medicago sativa, and LaHK1 from Lupinus albus, in nodule morphogenesis, senescence and stress response. LaHK1 expression increased during the first stages of lupin nodule development, while MsHK1 expression was localized in the meristem and the invasion zone of alfalfa nodules pointing to a role for CRs in nodule cell proliferation and differentiation. Both CRs were also induced during nodule senescence. MsHK1 expression increased under osmotic stress and both genes were induced following dark stress, indicating that CRs are also likely to play a significant role in the response to stress. We propose multiple roles for CRs which, when analyzed jointly with recent results from other authors, suggest coordinated cross-talk of different signaling systems.; Peer reviewed

A cytokinin receptor homologue is induced during root nodule organogenesis and senescence in Lupinus albus L.

Coba de la Peña, Teodoro; Cárcamo, Claudia B.; Almonacid, Luis; Zaballos, Ángel; Lucas, M. Mercedes; Balomenos, Dimitrios; Pueyo, José J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 450461 bytes; application/pdf
ENG
Relevância na Pesquisa
37.13%
6 pages; Here we report the isolation of a new cytokinin receptor homologue, LaHK1, from lupin (Lupinus albus) root nodules. LaHK1 transcript accumulation was detected in different plant organs, and expression was analyzed throughout nodule development. We observed notably higher expression in nodule primordia and young nodules compared to the root or to mature nodules. We also detected elevated transcript accumulation in naturally senescent nodules and in senescent nodules subjected to foliar dark stress. The results could be an indication of a putative role of this cytokinin receptor homologue in nodule development, from morphogenesis through senescence.; Peer reviewed

A salt stress-responsive cytokinin receptor homologue isolated from Medicago sativa nodules

Coba de la Peña, Teodoro; Cárcamo, Claudia B.; Almonacid, Luis; Zaballos, Ángel; Lucas, M. Mercedes; Balomenos, Dimitrios; Pueyo, José J.
Fonte: Springer Publicador: Springer
Tipo: Artículo Formato: 3764668 bytes; application/pdf
ENG
Relevância na Pesquisa
37.37%
11 pages and 8 figures; A new cytokinin receptor homologue, MsHK1, was isolated from Medicago sativa root nodules. MsHK1 expression was induced in alfalfa seedlings by exogenous application of the cytokinin trans-zeatin. Transcript accumulation was detected in diVerent plant organs. MsHK1 expression was induced by salt stress in alfalfa roots, leaves and nodules, and transcript accumulation in the vascular bundles pointed to a putative role in osmosensing for MsHK1 and/or other close cytokinin receptor homologues. Expression in the meristem and the invasion zone of the nodule suggest a role for cytokinin receptors in cytokinin sensing during nodule cell division and diferentation; Peer reviewed

Temporal and spatial order of events during the induction of cortical cell divisions in white clover by Rhizobium leguminosarum bv. trifolii inoculation or localized cytokinin addition

Mathesius, Ulrike; Charon, Celine; Rolfe, Barry; Kondorosi, Adam; Crespi, Martin
Fonte: APS Press Publicador: APS Press
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.48%
We examined the timing and location of several early root responses to Rhizobium leguminosarum bv. trifolii infection, compared with a localized addition of cytokinin in white clover, to study the role of cytokinin in early signaling during nodule initiation. Induction of ENOD40 expression by either rhizobia or cytokinin was similar in timing and location and occurred in nodule progenitor cells in the inner cortex. Inoculation of rhizobia in the mature root failed to induce ENOD40 expression and cortical cell divisions (ccd). Nitrate addition at levels repressing nodule formation inhibited ENOD40 induction by rhizobia but not by cytokinin. ENOD40 expression was not induced by auxin, an auxin transport inhibitor, or an ethylene precursor. In contrast to rhizobia, cytokinin addition was not sufficient to induce a modulation of the auxin flow, the induction of specific chalcone synthase genes, and the accumulation of fluorescent compounds associated with nodule initiation. However, cytokinin addition was sufficient for the localized induction of auxin-induced GH3 gene expression and the initiation of ccd. Our results suggest that rhizobia induce cytokinin-mediated events in parallel to changes in auxin-related responses during nodule initiation and support a role of ENOD40 in regulating ccd. We propose a model for the interactions of cytokinin with auxin...

The Cytokinin Requirement for Cell Division in Cultured Nicotiana plumbaginifolia Cells Can be Satisfied by Yeast Cdc25 Protein Tyrosine Phosphatase. Implications for Mechanisms of Cytokinin Response and Plant Development

Zhang, Kerong; John, Peter Crook; Diederich, Ludger
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.41%
Cultured cells of Nicotiana plumbaginifolia, when deprived of exogenous cytokinin, arrest in G2 phase prior to mitosis and then contain cyclin-dependent protein kinase (CDK) that is inactive because phosphorylated on tyrosine (Tyr). The action of cytokinin in stimulating the activation of CDK by removal of inhibitory phosphorylation from Tyr is not a secondary downstream consequence of other hormone actions but is the key primary effect of the hormone in its stimulation of cell proliferation, since cytokinin could be replaced by expression of cdc25, which encodes the main Cdc2 (CDK)-Tyr dephosphorylating enzyme of yeast (Saccharomyces cerevisiae). The cdc25 gene, under control of a steroid-inducible promoter, induced a rise in cdc25 mRNA, accumulation of p67Cdc25 protein, and increase in Cdc25 phosphatase activity that was measured in vitro with Tyr-phosphorylated Cdc2 as substrate. Cdc25 phosphatase activity peaked during mitotic prophase at the time CDK activation was most rapid. Mitosis that was induced by cytokinin also involved increase in endogenous plant CDK Tyr phosphatase activity during prophase, therefore indicating that this is a normal part of plant mitosis. These results suggest a biochemical mechanism for several previously described transgene phenotypes in whole plants and suggest that a primary signal from cytokinin leading to progression through mitosis is the activation of CDK by dephosphorylation of Tyr.