A CHEMICAL AND PHYSIOLOGICAL STUDY OF TRAUMATIN, A PLANT WOUND HORMONE.
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Journal Article↗
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Results for “PLANT HORMONES”
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Abscisic Acid and cytokinin contents of leaves in relation to salinity and relative humidity.
The question is raised whether the hormonal modifications in a plant exposed to osmotic root stress result directly from the decrease in water potential of the root environment or from disturbances of the plant's water balance.Tobacco plants were held for 24 hours under either high or low relative humidities, with or without salt. The amount of abscisic acid in the leaves of salinized plants rose markedly in low, but not in high, relative humidity. No change in the amount of extractable cytokinins was detected in any treatment. It is tentatively suggested that variations in the water content of leaves constitute a primary signal for modification of plant hormonal balance.
Journal Article↗
Biochemical and molecular analyses of gibberellin biosynthesis in fungi.
The plant hormone, gibberellin (GA), regulates plant growth and development. It was first isolated as a superelongation-promoting diterpenoid from the fungus, Gibberella fujikuroi. G. fujikuroi uses different GA biosynthetic intermediates from those in plants to produce GA3. Another class of GA-producing fungus, Phaeosphaeria sp. L487, synthesizes GA1 by using the same intermediates as those in plants. A molecular analysis of GA biosynthesis in Phaeosphaeria sp. has revealed that diterpene cyclase and cytochrome P450 monooxygenases were involved in the plant-like biosynthesis of GA1. Fungal ent-kaurene synthase is a bifunctional cyclase. Subsequent oxidation steps are catalyzed by P450s, leading to biologically active GA1. GA biosynthesis in plants is divided into three steps involving soluble enzymes and membrane-bound cytochrome P450. The activation of plant GAs is catalyzed by soluble 2-oxoglutarate-dependent dioxygenases, which is in contrast to the catalysis of fungal GA biosynthesis. This difference suggests that the origin of fungal GA biosynthesis is evolutionally independent of that in plants.
Catalysis↗
Effects of some growth hormones on plant vigour and volatile oil of Origanum majorana L.
Origanum majorana L. treated with either 50 or 100 mg/l of maleic hydrazide (MH), 2.4-dichlorophenoxy acetic acid (2.4-D), N-dimethylaminosuccinamic acid (B995), [2-chloroethyl]-trimethyl ammonium chloride (CCC), indol-3-yl-acetic acid (IAA) or gibberellic acid (GA3) in the presence or absence of 25 mg/l kinetin, showed that only 100 mg/l GA3 with or without kinetin was able to increase plant height than all other treatments and the controls. On the other hand, both IAA and GA3 concentrations and 2000 mg/l CCC markedly increased the dry weight of the plants in the absence of kinetin, whereas when kinetin was combined, only IAA in both concentrations increased the dry weight of the whole plants. Concerning essential oil %, the highest yields were obtained using 100 mg/l MH, 50 mg/l 2.4-D and 2000 mg/l CCC for leaves and 100 mg/l MH, 1000 mg/l B995 and 50 mg/l 2.4-D for flowers in the absence of kinetin, whereas in the presence of kinetin, the higher yields of essential oil were obtained by using 1000 mg/l B995 and 25 mg/l 2.4-D for flowers and only 50 mg/l 2.4-D for leaves.
Gibberellins↗
Phytoestrogens. Getting your hormones from plants.
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Journal Article↗
[The grain test, an old pregnancy test; effects of human and animal hormones on plants].
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Animals↗
The coming of age of sex hormones in plants.
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Animals↗
Gibberellin metabolism and signaling.
Gibberellins (GAs) are a family of plant hormones controlling many aspects of plant growth and development including stem elongation, germination, and the transition from vegetative growth to flowering. Cloning of the genes encoding GA biosynthetic and inactivating enzymes has led to numerous insights into the developmental regulation of GA hormone accumulation that is subject to both positive and negative feedback regulation. Genetic and biochemical analysis of GA-signaling genes has revealed that posttranslational regulation of DELLA protein accumulation is a key control point in GA response. The highly conserved DELLA proteins are a family of negative regulators of GA signaling that appear subject to GA-stimulated degradation through the ubiquitin-26S proteasome pathway. This review discusses the regulation of GA hormone accumulation and signaling in the context of its role in plant growth and development.
Gibberellins↗
Calcium Requirement for Ethylene-Dependent Responses.
Ethylene, a gaseous plant hormone, plays a role in plant development, defense, and climacteric fruit ripening. Both genetic and biochemical evidence suggest that the response of plants to ethylene is mediated by a specific ethylene receptor. The signal emanating from the receptor-effector complex is then presumably transduced via an unknown cascade pathway. We have used the plant pathogenesis response, exemplified by the induction of the pathogenesis-related gene chitinase, as a paradigm to investigate ethylene-dependent signal transduction in the plant cell. We showed that calcium is necessarily involved in the ethylene-mediated pathogenesis response. Blocking calcium fluxes with chelators inhibited ethylene-dependent induction of chitinase accumulation, but not ethylene independent induction. Artificially increasing cytosolic calcium levels by treatments with the calcium ionophore ionomycin or the calcium pump blocker thapsigargin stimulated chitinase accumulation. Plants grown in calcium-poor soil showed a 10-fold reduction in leaf extractable calcium. Their leaves exhibited a reduced pathogenesis reaction to ethylene and were impaired in another hormone response mediated by calcium, i.e., abscisic acid-controlled closure of guard cells. The addition of calcium to leaves excised from calcium-deficient plants restored their sensitivity to ethylene. Ethylene participates in the control of seedling growth, promoting the so-called "triple response" that results in distinct morphological development, such as hypocotyl hook formation. This effect, similar to the ethylene-promoted pathogenesis response, was found to be calcium dependent. The results indicate that calcium is required for a variety of ethylene-dependent processes.
Journal Article↗
Effect of hormones and related compounds on the multiplication of Tetrahymena.
The vertebrate hormone triiodothyronine, the commonly occurring animal and plant hormone serotonin, and the plant alkaloid gramine, chemically related to the latter, stimulated the multiplication of Tetrahymena. Neither epinephrine nor gibberellin had such an effect. These experimental observations support the previous suggestion that unicellular animals possess structures capable of responding to certain hormones, which do not seem to elicit specific responses of the unicellular animal, but rather act through the activation of certain general functions.
Alkaloids↗
The GUS reporter-aided analysis of the promoter activities of Arabidopsis ACC synthase genes AtACS4, AtACS5, and AtACS7 induced by hormones and stresses.
Ethylene biosynthesis in higher plants is regulated developmentally and environmentally. To investigate the regulation of ACC synthase gene expression, the promoters of Arabidopsis ACS genes, AtACS4, AtACS5, and AtACS7, were fused to a GUS reporter gene, and the recombinant transgenes were introduced into Arabidopsis to produce three groups of AtACS::GUS transgenic plants. Histochemic and fluorometric study of these transgenic plants revealed that promoters of AtACS4, AtACS, and AtACS7 are all active in dark-germinated seedlings. AtACS5 has the highest promoter activity in leaves of 2-week-old light-grown seedlings among the three AtACS genes studied. In the mature leaves, AtACS4 and AtACS7 genes are expressed in both veins and areoles, whereas AtACS5 is expressed at a higher level in the areoles and epidermal cells surrounding trichomes. The promoter activities of all these AtACS genes are found in the reproductive organs. AtACS5 and AtACS7 are highly expressed in petals, sepals, carpels, stamens, cauline leaves, inflorescence stems, and siliques, while AtACS4 expression is undetectable in the petals of open flowers. All three AtACS genes are expressed in root tissue. In the 2-week-old light-grown Arabidopsis, the AtACS4 promoter is responsive to the plant hormones IAA, ethylene, and ABA, and to darkness and wounding; the AtACS5 promoter to IAA, ABA, salt, high temperature, and wounding; and the AtACS7 promoter to GA3, ethylene, and ABA, and to darkness and salt. Low-temperature treatment abolishes the darkness-induced AtACS7 gene expression, but not that of AtACS4. Each AtACS gene has a unique expression profile during growth and development. It appears that at any developmental stage or any growth period of Arabidopsis, there is always a member of AtACS multigene family that is actively expressed.
Arabidopsis↗
A transcriptome-based characterization of habituation in plant tissue culture.
For the last 50 years, scientists have recognized that varying ratios of the plant hormones cytokinin and auxin induce plant cells to form particular tissues: undifferentiated calli, shoot structures, root structures, or a whole plant. Proliferation of undifferentiated callus tissue, greening, and the formation of shoot structures are all cytokinin-dependent processes. Habituation refers to a naturally occurring phenomenon whereby callus cultures, upon continued passage, lose their requirement for cytokinin. Earlier studies of calli with a higher-than-normal cytokinin content indicate that overproduction of cytokinin by the culture tissues is a possible explanation for this acquired cytokinin independence. A transcriptome-based analysis of a well established habituated Arabidopsis (Arabidopsis thaliana) cell culture line was undertaken, to explore genome-wide expression changes underlying the phenomenon of habituation. Increased levels of expression of the cytokinin receptor CRE1, as well as altered levels of expression of several other genes involved in cytokinin signaling, indicated that naturally acquired deregulation of cytokinin-signaling components could play a previously unrecognized role in habituation. Up-regulation of several cytokinin oxidases, down-regulation of several known cytokinin-inducible genes, and a lack of regulation of the cytokinin synthases indicated that increases in hormone concentration may not be required for habituation. In addition, up-regulation of the homeodomain transcription factor FWA, transposon-related elements, and several DNA- and chromatin-modifying enzymes indicated that epigenetic changes contribute to the acquisition of cytokinin habituation.
Amino Acid Sequence↗
Gain of function assays identify non-rol genes from Agrobacterium rhizogenes TL-DNA that alter plant morphogenesis or hormone sensitivity.
This study tested the morphogenetic potential of 15 open reading frames of the TL-DNA of Agrobacterium rhizogenes strain HRI. These open reading frames were expressed individually under the control of the 35S RNA promoter in transgenic tobacco plants (Nicotiana tabacum L.). Expression of three T-DNA loci, ORF3n, ORF8 and ORF13, alters plant morphogenesis or the response of transgenic tissues to plant hormones. ORF3n transgenic plants are characterized by retarded flowering, altered internode elongation, altered leaf shape and, in particular, leaf tip necrosis. ORF3n and ORF8 expression reduces the sensitivity to auxin and cytokinin in combination or auxin alone. Tetracycline-dependent expression of ORF13 overcomes a selection of low levels of expression during plant regeneration and reveals a strong inhibitory effect of the ORF13 gene product on cell division and cell elongation. We conclude that the A. rhizogenes TL-DNA harbors genetic information that is important for pathogenicity apart from the well studied rol genes. We propose that these genes play mainly a negative regulatory role during pathogenesis. Moreover, these loci might be relevant to successful infections in specific host plants.
Amino Acid Sequence↗
A novel wound-responsive cis-element, VWRE, of the vascular system-specific expression of a tobacco peroxidase gene, tpoxN1.
The wound-induced expression of tpoxN1, encoding a tobacco peroxidase, is unique because of its vascular system-specific expression and insensitivity to known wound-signal compounds such as jasmonic acid, ethylene, and plant hormones [Sasaki et al. (2002) Plant Cell Physiol 43:108-117]. To study the mechanism of expression, the 2-kbp tpoxN1 promoter region and successive 5'-deletion of the promoter were introduced as GUS fusion genes into tobacco plants. Analysis of GUS activity in transgenic plants indicated that a vascular system-specific and wound-responsive cis-element (VWRE) is present at the -239/-200 region of the promoter. Gel mobility shift assays suggested that a nuclear factor(s) prepared from wounded tobacco stems binds a 14-bp sequence (-229/-215) in the -239/-200 region in a sequence-specific manner. A mutation in this 14-bp region of the -239 promoter fragment resulted in a considerable decrease in wound-responsive GUS activity in transgenic plants. An 11-bp sequence, which completely overlaps with the 14-bp sequence, was found in the 5' distal region (-420/-410) and is thought to contribute to the wound-induced expression together with the 14-bp. The -114-bp core promoter of the tpoxN1 gene was indispensable for wound-induced expression, indicating that the 14-bp region is a novel wound-responsive cis-element VWRE, which may work cooperatively with other factors in the promoter.
Base Sequence↗
Pattern formation of leaf veins by the positive feedback regulation between auxin flow and auxin efflux carrier.
The generation of vascular pattern formation in plants is an interesting process of pattern formation in organisms. It is well known that the plant hormone auxin is involved in plant vascular differentiation and that the PIN1 protein, an auxin efflux carrier, localizes to one side of the cell membrane. Several hypotheses have been proposed to explain the formation of leaf venation. One is the canalization hypothesis that is based on the assumption that a positive feedback regulation exists between the flow of a signal molecule and the capacity of its flow. Here, we attempted to integrate the canalization hypothesis and experimental data. We investigated models of the positive feedback regulation between the auxin flow and PIN1 localization. Model 1, with conserved PIN1 amount in each cell, can generate a branching pattern similar to that of plant leaf venation. We introduced the diffusible enhancer "e" into the model as unknown factor. The obtained patterns show a quasi-periodic distribution of auxin flow paths, when the model dynamics includes domain growth. In order to understand the early initiation process that generates an inhomogeneity from an almost homogeneous distribution, we introduced model 2, a simplified version of model 1. Model 2 can generate inhomogeneity with a parameter dependency similar to that of model 1. To analyse parameter condition required for pattern development, approximated equations are obtained from model 2. The isocline analysis of the equations without spatial structure shows that the inhomogeneous distribution occurs from an almost homogeneous distribution. This parameter condition for generating inhomogeneity is consistent with the results of models 1 and 2.
Arabidopsis Proteins↗
Plant response regulators implicated in signal transduction and circadian rhythm.
The so-called 'response regulators' were originally discovered as common components of the widespread histidine (His)-->aspartate (Asp) phosphorelay signal transduction system in prokaryotes. Through the course of evolution, higher plants have also come to employ such prokaryotic response regulators (RRs) for their own signal transduction, such as the elicitation of plant hormone (e.g. cytokinin) responses. Furthermore, plants have evolved their own atypical variants of response regulators, pseudo response regulators (PRRs), which are used to modulate sophisticated biological processes, including circadian rhythms and other light-signal responses. Recent studies using the model plant Arabidopsis thaliana have begun to shed light on the interesting functions of these plant response regulators.
Arabidopsis↗
Efficiency of different methods of extraction and purification of cytokinins.
The increasing use of advanced methods, such as mass spectrometry, for the determination of cytokinins has raised special requirements for the extraction and purification of this class of plant hormones. Extraction of Arabidopsis thaliana plants with three different solvents, [80% (v/v) MeOH, Bieleski's MCF-7, and modified Bieleski's] provided similar yields of most analyzed cytokinins determined by high-performance liquid chromatography-tandem mass spectrometry (HPLC/MS/MS). However, the extraction with a modified Bieleski's solvent (MeOH-HCO2H-H2O [15:1:4, v/v/v]) gave the highest responses of deuterated cytokinins (used as test compounds) in plant extracts as compared to the responses of pure deuterated standards (relative internal standard response, RISR). Purification of cytokinins using Oasis MCX sorbent with reversed-phase and cation-exchange characteristics, in comparison to the DEAE Sephadex RP-C18 method, provided higher levels of zeatin riboside monophosphate and similar levels of cytokinin bases, ribosides and glucosides. Using this method the content of UV-absorbing contaminates was decreased by about 90% and the RISR values of all tested cytokinin standards but riboside monophosphates were increased about two-fold. The former method provided preparations more suitable for HPLC/MS/MS analysis with respect to simplicity and sample purity.
Arabidopsis↗
The diageotropica gene differentially affects auxin and cytokinin responses throughout development in tomato.
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 cells. 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, indicating that auxin and cytokinin regulate plant growth through both shared and separate signaling pathways.
2,4-Dichlorophenoxyacetic Acid↗