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1.
Curr Biol ; 23(1): 53-7, 2013 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-23219726

RESUMO

Stomata are pores on the leaf surface, bounded by two guard cells, which control the uptake of CO(2) for photosynthesis and the concomitant loss of water vapor. In 1898, Francis Darwin showed that stomata close in response to reduced atmospheric relative humidity (rh); however, our understanding of the signaling pathway responsible for coupling changes in rh to alterations in stomatal aperture is fragmentary. The results presented here highlight the primacy of abscisic acid (ABA) in the stomatal response to drying air. We show that guard cells possess the entire ABA biosynthesis pathway and that it appears upregulated by positive feedback by ABA. When wild-type Arabidopsis and the ABA-deficient mutant aba3-1 were exposed to reductions in rh, the aba3-1 mutant wilted, whereas the wild-type did not. However, when aba3-1 plants, in which ABA synthesis had been specifically rescued in guard cells, were challenged with dry air, they did not wilt. These data indicate that guard cell-autonomous ABA synthesis is required for and is sufficient for stomatal closure in response to low rh. Guard cell-autonomous ABA synthesis allows the plant to tailor leaf gas exchange exquisitely to suit the prevailing environmental conditions.


Assuntos
Ácido Abscísico/biossíntese , Arabidopsis/fisiologia , Umidade , Estômatos de Plantas/fisiologia , Arabidopsis/genética , Arabidopsis/metabolismo , Dióxido de Carbono/metabolismo , Retroalimentação Fisiológica , Fotossíntese , Transcriptoma
2.
J Exp Bot ; 63(18): 6421-30, 2012 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-23136167

RESUMO

Resolving the physiological mechanisms by which rhizobacteria enhance plant growth is difficult, since many such bacteria contain multiple plant growth-promoting properties. To understand further how the 1-aminocyclopropane-1-carboxylate (ACC) deaminase (ACCd)-containing rhizobacterium Variovorax paradoxus 5C-2 affects plant growth, the flows and partitioning of mineral nutrients and abscisic acid (ABA) and ABA metabolism were studied in pea (Pisum sativum) plants following rhizosphere bacterial inoculation. Although root architecture was not affected, inoculation increased root and shoot biomass, and stomatal conductance, by 20, 15, and 24%, respectively, and increased N, P, K, Ca, and Mg uptake by 16, 81, 50, 46, and 58%, respectively. P deposition in inoculated plant roots was 4.9 times higher than that in uninoculated controls. Rhizobacterial inoculation increased root to shoot xylem flows and shoot to root phloem flows of K by 1.8- and 2.1-fold, respectively. In control plants, major sinks for K deposition were the roots and upper shoot (43% and 49% of total uptake, respectively), while rhizobacterial inoculation increased K distribution to the lower shoot at the expense of other compartments (xylem, phloem, and upper shoot). Despite being unable to metabolize ABA in vitro, V. paradoxus 5C-2 decreased root ABA concentrations and accumulation by 40-60%. Although inoculation decreased xylem ABA flows, phloem ABA flows increased. Whether bacterial ACCd attenuates root to shoot ABA signalling requires further investigation, since ABA is critical to maintain growth of droughted plants, and ACCd-containing organisms have been advocated as a means of minimizing growth inhibition of plants in drying soil.


Assuntos
Ácido Abscísico/metabolismo , Comamonadaceae/fisiologia , Pisum sativum/microbiologia , Pisum sativum/fisiologia , Reguladores de Crescimento de Plantas/metabolismo , Aclimatação , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Carbono-Carbono Liases/genética , Carbono-Carbono Liases/metabolismo , Comamonadaceae/genética , Modelos Biológicos , Pisum sativum/genética , Reguladores de Crescimento de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Raízes de Plantas/microbiologia , Brotos de Planta/crescimento & desenvolvimento , Brotos de Planta/metabolismo
3.
New Phytol ; 194(2): 402-415, 2012 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-22296281

RESUMO

During harvest, fleshy berry tomato fruits (Solanum lycopersicum) were wounded at their stem scar. Within 3 d, this wound was rapidly sealed by a process covering the wound site with a membranous layer which effectively protects the tomato fruit from excessive water loss, nutrient elution and the entry of pathogens. Chemical analysis of the de novo synthesized stem scar tissue revealed the presence of aromatic and aliphatic components characteristic of the biopolyester suberin. Gene expression patterns associated with suberization were identified at the stem scar region. Changes in the relative abundance of different transcripts suggested a potential involvement of the plant hormone abscisic acid (ABA) in the wound-healing processes. The amount of ABA present in the stem scar tissue showed a significantly increased level during wound healing, whereas ABA-deficient mutants notabilis, flacca and sitiens were largely devoid of this rise in ABA levels. The mutant fruits showed a retarded and less efficient suberization response at the stem scar wound, whereas the rate and strength of this response were positively correlated with ABA content. These results clearly indicate in vivo the involvement of ABA in the suberization-based wound-healing processes at the stem scar tissue of tomato fruits.


Assuntos
Ácido Abscísico/farmacologia , Frutas/metabolismo , Lipídeos/química , Caules de Planta/metabolismo , Solanum lycopersicum/efeitos dos fármacos , Solanum lycopersicum/metabolismo , Frutas/citologia , Frutas/efeitos dos fármacos , Frutas/microbiologia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Íons , Solanum lycopersicum/genética , Solanum lycopersicum/microbiologia , Membranas/efeitos dos fármacos , Permeabilidade/efeitos dos fármacos , Doenças das Plantas/microbiologia , Caules de Planta/citologia , Caules de Planta/efeitos dos fármacos , Caules de Planta/microbiologia , Água , Cicatrização/efeitos dos fármacos
4.
J Exp Bot ; 62(14): 4965-74, 2011 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-21772019

RESUMO

The early (2-4 d) effects of slowly imposed soil water deficit on Lupinus albus photosynthetic performance, carbon metabolism, and hormonal balance in different organs (leaf blade, stem stele, stem cortex, and root) were evaluated on 23-d-old plants (growth chamber assay). Our work shows that several metabolic adjustments occurred prior to alteration of the plant water status, implying that water deficit is perceived before the change in plant water status. The slow, progressive decline in soil water content started to be visible 3 d after withholding water (3 DAW). The earliest plant changes were associated with organ-specific metabolic responses (particularly in the leaves) and with leaf conductance and only later with plant water status and photosynthetic rate (4 DAW) or photosynthetic capacity (according to the Farquhar model; 6 DAW). Principal component analysis (PCA) of the physiological parameters, the carbohydrate and the hormone levels and their relative values, as well as leaf water-soluble metabolites full scan data (LC-MS/MS), showed separation of the different sampling dates. At 6 DAW classically described stress responses are observed, with plant water status, ABA level, and root hormonal balance contributing to the separation of these samples. Discrimination of earlier stress stages (3 and 4 DAW) is only achieved when the relative levels of indole-3-acetic acid (IAA), cytokinins (Cks), and carbon metabolism (glucose, sucrose, raffinose, and starch levels) are taken into account. Our working hypothesis is that, in addition to single responses (e.g. ABA increase), the combined alterations in hormone and carbohydrate levels play an important role in the stress response mechanism. Response to more advanced stress appears to be associated with a combination of cumulative changes, occurring in several plant organs. The carbohydrate and hormonal balance in the leaf (IAA to bioactive-Cks; soluble sugars to IAA and starch to IAA; relative abundances of the different soluble sugars) flag the initial responses to the slight decrease in soil water availability (10-15% decrease). Further alterations in sucrose to ABA and in raffinose to ABA relative values (in all organs) indicate that soil water availability continues to decrease. Such alterations when associated with changes in the root hormone balance indicate that the stress response is initiated. It is concluded that metabolic balance (e.g. IAA/bioactive Cks, carbohydrates/IAA, sucrose/ABA, raffinose/ABA, ABA/IAA) is relevant in triggering adjustment mechanisms.


Assuntos
Carbono/metabolismo , Lupinus/fisiologia , Fotossíntese , Reguladores de Crescimento de Plantas/metabolismo , Água/metabolismo , Citocininas/metabolismo , Ácidos Indolacéticos/metabolismo , Solo/análise , Estresse Fisiológico
5.
Planta ; 233(1): 87-94, 2011 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-20924765

RESUMO

We studied the possible involvement of ABA in the control of water relations under conditions of increased evaporative demand. Warming the air by 3°C increased stomatal conductance and raised transpiration rates of hydroponically grown Triticum durum plants while bringing about a temporary loss of relative water content (RWC) and immediate cessation of leaf extension. However, both RWC and extension growth recovered within 30 min although transpiration remained high. The restoration of leaf hydration and growth were enabled by increased root hydraulic conductivity after increasing the air temperature. The use of mercuric chloride (an inhibitor of water channels) to interfere with the rise on root hydraulic conductivity hindered the restoration of extension growth. Air warming increased ABA content in roots and decreased it in shoots. We propose this redistribution of ABA in favour of the roots which increased the root hydraulic conductivity sufficiently to permit rapid recovery of shoot hydration and leaf elongation rates without the involvement of stomatal closure. This proposal is based on known ability of ABA to increase hydraulic conductivity confirmed in these experiments by measuring the effect of exogenous ABA on osmotically driven flow of xylem sap from the roots. Accumulation of root ABA was mainly the outcome of increased export from the shoots. When phloem transport in air-warmed plants was inhibited by cooling the shoot base this prevented ABA enrichment of the roots and favoured an accumulation of ABA in the shoot. As a consequence, stomata closed.


Assuntos
Ácido Abscísico/metabolismo , Raízes de Plantas/fisiologia , Transpiração Vegetal/fisiologia , Triticum/fisiologia , Água/fisiologia , Biomassa , Floema/fisiologia , Estômatos de Plantas/fisiologia , Plântula/fisiologia , Temperatura , Triticum/crescimento & desenvolvimento , Xilema/fisiologia
6.
Plant J ; 62(6): 1072-82, 2010 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-20345603

RESUMO

Uptake of CO(2) by the leaf is associated with loss of water. Control of stomatal aperture by volume changes of guard cell pairs optimizes the efficiency of water use. Under water stress, the protein kinase OPEN STOMATA 1 (OST1) activates the guard-cell anion release channel SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1), and thereby triggers stomatal closure. Plants with mutated OST1 and SLAC1 are defective in guard-cell turgor regulation. To study the effect of stomatal movement on leaf turgor using intact leaves of Arabidopsis, we used a new pressure probe to monitor transpiration and turgor pressure simultaneously and non-invasively. This probe permits routine easy access to parameters related to water status and stomatal conductance under physiological conditions using the model plant Arabidopsis thaliana. Long-term leaf turgor pressure recordings over several weeks showed a drop in turgor during the day and recovery at night. Thus pressure changes directly correlated with the degree of plant transpiration. Leaf turgor of wild-type plants responded to CO(2), light, humidity, ozone and abscisic acid (ABA) in a guard cell-specific manner. Pressure probe measurements of mutants lacking OST1 and SLAC1 function indicated impairment in stomatal responses to light and humidity. In contrast to wild-type plants, leaves from well-watered ost1 plants exposed to a dry atmosphere wilted after light-induced stomatal opening. Experiments with open stomata mutants indicated that the hydraulic conductance of leaf stomata is higher than that of the root-shoot continuum. Thus leaf turgor appears to rely to a large extent on the anion channel activity of autonomously regulated stomatal guard cells.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Estômatos de Plantas/fisiologia , Proteínas Quinases/metabolismo , Água/fisiologia , Ácido Abscísico/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Dióxido de Carbono/metabolismo , Luz , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Mutação , Fotossíntese , Transpiração Vegetal , Pressão , Proteínas Quinases/genética
9.
Plant J ; 59(1): 39-51, 2009 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-19309463

RESUMO

During leaf senescence, resources are recycled by redistribution to younger leaves and reproductive organs. Candidate pathways for the regulation of onset and progression of leaf senescence include ubiquitin-dependent turnover of key proteins. Here, we identified a novel plant U-box E3 ubiquitin ligase that prevents premature senescence in Arabidopsis plants, and named it SENESCENCE-ASSOCIATED E3 UBIQUITIN LIGASE 1 (SAUL1). Using in vitro ubiquitination assays, we show that SAUL1 has E3 ubiquitin ligase activity. We isolated two alleles of saul1 mutants that show premature senescence under low light conditions. The visible yellowing of leaves is accompanied by reduced chlorophyll content, decreased photochemical efficiency of photosystem II and increased expression of senescence genes. In addition, saul1 mutants exhibit enhanced abscisic acid (ABA) biosynthesis. We show that application of ABA to Arabidopsis is sufficient to trigger leaf senescence, and that this response is abolished in the ABA-insensitive mutants abi1-1 and abi2-1, but enhanced in the ABA-hypersensitive mutant era1-3. We found that increased ABA levels coincide with enhanced activity of Arabidopsis aldehyde oxidase 3 (AAO3) and accumulation of AAO3 protein in saul1 mutants. Using label transfer experiments, we showed that interactions between SAUL1 and AAO3 occur. This suggests that SAUL1 participates in targeting AAO3 for ubiquitin-dependent degradation via the 26S proteasome to prevent premature senescence.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Ubiquitina-Proteína Ligases/metabolismo , Ácido Abscísico/metabolismo , Aldeído Oxidase/metabolismo , Alelos , Arabidopsis/enzimologia , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , DNA Bacteriano , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Luz , Mutagênese Insercional , Mutação , Folhas de Planta/fisiologia , RNA de Plantas/genética , Ubiquitina-Proteína Ligases/genética , Ubiquitinação
10.
Planta ; 229(2): 299-309, 2009 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-18946679

RESUMO

In this study the impact of salt stress on the physiology and wood structure of the salt-sensitive Populus x canescens was investigated. Two weeks of salt stress altered wood anatomy significantly. The xylem differentiation zone was reduced and the resulting vessels exhibited reduced lumina. To understand this phenomenon, ion composition, levels of corresponding transcripts and of the stress hormone ABA were analysed. With increasing sodium and chloride concentrations, a general reduction of potassium was found in roots and shoots, but not in leaves. Consequently, the corresponding K+ channel transcripts in roots favoured K+ release. The overall osmolarity in leaves was up to fourfold higher than in roots or shoots. Therefore, adjustment of the K+/Na+ balance seemed not to be required in leaves. Sodium increased gradually from roots to shoots and then to leaves indicating that sodium storage took place first in roots, then in shoots, and finally in leaves to protect photosynthesis from salt effects as long as possible. Since leaf abscisic acid levels markedly increased, stomatal closure seemed to limit CO2 uptake. As a consequence, diminished nutrient supply to the cambium in combination with lowered shoot K+ content led to decreased vessel lumina, and a reduction of the radial cambium was observed. Thus, xylem differentiation was curtailed and the development of full size vessels was impaired.


Assuntos
Diferenciação Celular/efeitos dos fármacos , Cruzamentos Genéticos , Populus/citologia , Populus/efeitos dos fármacos , Cloreto de Sódio/farmacologia , Estresse Fisiológico/efeitos dos fármacos , Xilema/citologia , Ácido Abscísico/metabolismo , Arabidopsis/genética , Transporte Biológico/efeitos dos fármacos , Elementos Químicos , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Malatos/metabolismo , Filogenia , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Raízes de Plantas/citologia , Raízes de Plantas/efeitos dos fármacos , Populus/genética , Potássio/metabolismo , Canais de Potássio/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Sódio/metabolismo , Madeira/citologia , Madeira/efeitos dos fármacos , Xilema/efeitos dos fármacos , Xilema/ultraestrutura
11.
New Phytol ; 180(3): 642-651, 2008.
Artigo em Inglês | MEDLINE | ID: mdl-18700860

RESUMO

* Proposed mechanisms of embolism recovery are controversial for plants that are transpiring while undergoing cycles of dehydration and rehydration. * Here, water stress was imposed on grapevines (Vitis vinifera), and the course of embolism recovery, leaf water potential (Psi(leaf)), transpiration (E) and abscisic acid (ABA) concentration followed during the rehydration process. * As expected, Psi(leaf) and E decreased upon water stress, whereas xylem embolism and leaf ABA concentration increased. Upon rehydration, Psi(leaf) recovered in 5 h, whereas E fully recovered only after an additional 48 h. The ABA content of recovering leaves was higher than in droughted controls, both on the day of rewatering and the day after, suggesting that ABA accumulated in roots during drought was delivered to the rehydrated leaves. In recovering plants, xylem embolism in petioles, shoots, and roots decreased during the 24 h following rehydration. * A model is proposed to describe plant recovery after rehydration based on three main points: embolism repair occurs progressively in shoots and further in roots and in petioles, following an almost full recovery of Psi(leaf); hydraulic conductance recovers during diurnal transpiring hours, when formation and repair of embolisms occurs in all plant organs; an ABA residual signal in rehydrated leaves hinders stomatal opening even when water relations have recovered, suggesting that an ABA-induced transpiration control promotes gradual embolism repair in rehydrated grapevines.


Assuntos
Ácido Abscísico/metabolismo , Desidratação , Transpiração Vegetal/fisiologia , Vitis/fisiologia , Água/fisiologia , Xilema/fisiologia , Adaptação Fisiológica , Transporte Biológico , Secas , Estômatos de Plantas/fisiologia , Estruturas Vegetais/fisiologia , Transdução de Sinais
12.
Physiol Plant ; 134(1): 13-21, 2008 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-18419740

RESUMO

Boron (B) is an essential nutrient required for plant growth and physiological processes. Long-distance B transport is facilitated by the formation of B-polyol complexes. We investigated B uptake and distribution in response to differing levels of exogenous nitrogen supply in the hemiparasitic association between Rhinanthus minor and Hordeum vulgare (barley) and in unparasitised barley and single Rhinanthus plants. In this system, the polyol mannitol is the major assimilate in Rhinanthus, whereas polyols are not detectable in barley. Furthermore, previous studies have shown that the accumulation of polyols within Rhinanthus is negatively affected by the application of exogenous nitrogen. Within the association, the strongest accumulation of B was detected in lateral buds and inflorescences of Rhinanthus, consistent with the greatest B demand in strong sink organs supplied through the phloem that contain high concentrations of mannitol. In the host, the strongest B accumulation was found in xylem-supported leaf lamellae. Roots and sheaths did not accumulate substantial amounts of B, while re-circulation of B through the phloem vessels accounted for only 10% (unparasitised) and 8% (parasitised) of the xylem sap-imported B in the mannitol-free barley hosts. In contrast, 53% (attached) and 39% (in the absence of a host) of the xylem sap-imported B was re-circulated in the phloem in the mannitol-rich Rhinanthus. We therefore present the first quantitative uptake and flow models of long-distance B transport in polyol-rich and polyol-free plants. Our findings are consistent with a close relationship between B re-translocation and mannitol concentrations in phloem vessels.


Assuntos
Boro/metabolismo , Hordeum/metabolismo , Orobanchaceae/metabolismo , Polímeros/metabolismo , Transporte Biológico , Hordeum/crescimento & desenvolvimento , Manitol/metabolismo , Modelos Biológicos , Nitrogênio/metabolismo , Orobanchaceae/crescimento & desenvolvimento , Floema/metabolismo , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo
13.
J Exp Bot ; 59(4): 917-25, 2008.
Artigo em Inglês | MEDLINE | ID: mdl-18308739

RESUMO

The high quality of leguminous hosts for the parasitic plant Rhinanthus minor (in terms of growth and fecundity), compared with forbs (non-leguminous dicots) has long been assumed to be a function of the legume's ability to fix atmospheric nitrogen (N) from the air and the potential for direct transfer of compatible amino compounds to the parasite. Using associations between Rhinanthus minor and Vicia faba (Fabaceae) that receive N either exclusively via symbiotic associations with rhizobia supplying organic N fixed from N(2) or exclusively through the supply of inorganic nitrate to the substrate, the underlying reasons for the quality of legumes as hosts for this parasite are unravelled. It is shown that sole dependence of the host, V. faba, on N fixation results in lower growth of the attached parasite than when the host is grown in a substrate supplied exclusively with inorganic N. In contrast, the host plants themselves achieved a similar biomass irrespective of their N source. The physiological basis for this is investigated in terms of N and abscisic acid (ABA) partitioning, haustorial penetration, and xylem sap amino acid profiles. It is concluded that legume N fixation does not underpin the quality of legumes as hosts for Rhinanthus but rather the well-developed haustorium formed by the parasite, coupled with the lack of defensive response of the host tissues to the invading haustorium and the presence of sufficient nitrogenous compounds in the xylem sap accessible to the parasite haustoria, would appear to be the primary factors influencing host quality of the legumes.


Assuntos
Fixação de Nitrogênio/fisiologia , Orobanchaceae/metabolismo , Vicia faba/metabolismo , Aminoácidos/metabolismo , Biomassa , Orobanchaceae/crescimento & desenvolvimento , Rhizobiaceae/fisiologia , Vicia faba/microbiologia , Xilema/metabolismo
14.
Plant Physiol Biochem ; 46(1): 64-70, 2008 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-18042393

RESUMO

Leaves of the mistletoe Viscum album (L.) show a high rate of transpiration, even when the host is under severe drought stress. The hypothesis that a strong control of ABA influx from the xylem sap of the host into the mistletoe prevents stomatal closure in mistletoe leaves was tested under the following conditions: sections of poplar twigs carrying a mistletoe were perfused with artificial xylem sap that contained different ABA concentrations and both transpiration and ABA levels were analysed in mistletoe leaves. Despite variation by a factor of 10(4), the ABA content of the host xylem did not affect ABA levels, leaf transpiration, CO(2) assimilation, WUE, or the degree of stomatal aperture in mistletoe leaves. These observations support the hypothesis of a strong control of ABA influx from the host of the xylem into the mistletoe, although degradation of ABA before it enters the mistletoe leaves cannot be excluded. This mechanism may ensure a water and nutritional status favourable for the mistletoe, even if the water status of the host is impaired. Despite the lack of short-term sensitivity of ABA levels in mistletoe leaves to even strong changes of ABA levels in the xylem sap of the host, ABA levels in mistletoe leaves were relatively high compared to ABA levels in the leaves of several tree species including poplar. Since significant transpiration of the mistletoe leaves was observed despite high ABA levels, a diminished sensitivity of the stomata of mistletoe leaves to ABA has to be concluded. The stomatal density of adaxial Viscum leaves of 89+/-23 stomata per mm is lower than those reported in a study performed at the end of the 19th century.


Assuntos
Ácido Abscísico/metabolismo , Dióxido de Carbono/metabolismo , Estômatos de Plantas/fisiologia , Transpiração Vegetal/fisiologia , Populus/metabolismo , Viscum album/fisiologia , Xilema/metabolismo , Ácido Abscísico/química , Ácido Abscísico/farmacologia , Desastres , Interações Hospedeiro-Parasita/efeitos dos fármacos , Interações Hospedeiro-Parasita/fisiologia , Reguladores de Crescimento de Plantas/química , Reguladores de Crescimento de Plantas/metabolismo , Reguladores de Crescimento de Plantas/farmacologia , Transpiração Vegetal/efeitos dos fármacos , Populus/química , Populus/parasitologia , Água/metabolismo , Xilema/química
15.
J Exp Bot ; 59(1): 37-43, 2008.
Artigo em Inglês | MEDLINE | ID: mdl-17595196

RESUMO

Abscisic acid (ABA) is a stress signal, which moves in the xylem from the roots to the aerial parts of the plant, where it regulates stomatal movement and the activity of shoot meristems. Root growth-promoting microorganisms in the rhizosphere, lateral ABA flows in the root cortex across apoplastic barriers, ABA redistribution in the stem, leaf apoplastic pH values, and the action of beta-glucosidases, both in the apoplast and the cytosol of the mesophyll, play an important role in the regulation of signal intensity. The significance of abscisic acid glucose ester as a long-distance stress signal is discussed.


Assuntos
Ácido Abscísico/metabolismo , Reguladores de Crescimento de Plantas/metabolismo , Plantas/metabolismo , Transdução de Sinais/fisiologia , Xilema/metabolismo , Raízes de Plantas/metabolismo
16.
Plant Physiol ; 145(3): 853-62, 2007 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-17827272

RESUMO

Crown gall tumors induced by Agrobacterium tumefaciens represent a sink that has to be provided with nutrients and water by the host plant. The lack of an intact epidermis or cuticle results in uncontrolled loss of water. However, neither the tumor nor the host plant displays wilting. This phenomenon points to drought adaptation in both tumors and the crown gall host plant. To understand the underlying molecular mechanisms of protection against desiccation the gene expression pattern of Arabidopsis (Arabidopsis thaliana) tumors was integrated with the profile of stress metabolites: Arabidopsis tumors accumulated high amounts of abscisic acid (ABA), the ethylene precursor aminocyclopropyl carboxylic acid, osmoprotectants, and form a suberized periderm-like protective layer. Suberization of the outer tumor cell layers most likely is mediated by ABA since external application of ABA induced suberization of Arabidopsis roots. However, the expression level of the classical marker genes, known to respond to drought stress and/or ABA, was lower in tumors. Instead another set of drought and/or ABA-inducible genes was more highly transcribed. Elevated transcription of several ABA-dependent aquaporin genes might indicate that ABA controls the water balance of the tumor. The retarded tumor growth on abi and aba mutant plants underlined the importance of a tumor-specific ABA signaling pathway. Taken together, we propose that ABA is an important signal for protection of tumors against desiccation and thus supports tumor development.


Assuntos
Ácido Abscísico/metabolismo , Arabidopsis/metabolismo , Arabidopsis/microbiologia , Tumores de Planta/microbiologia , Rhizobium/fisiologia , Água/metabolismo , Ácido Abscísico/farmacologia , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Dessecação , Desastres , Perfilação da Expressão Gênica , Regulação da Expressão Gênica de Plantas , Pressão Osmótica
17.
Physiol Plant ; 131(2): 311-21, 2007 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-18251902

RESUMO

This study investigated the mechanisms of salt resistance of four maize (Zea mays L.) hybrids [cultivar (cv.) Pioneer 3906 and newly developed hybrids SR03, SR12 and SR13] during the first phase of salt stress. Plants were grown in aerated nutrient solutions at 1 mM Na+ (control) and 100 mM Na+ (salt stress). Stress was imposed in 25 mM steps and plants were harvested after 2 days at 100 mM Na+. At 100 mM Na+ the area of the fourth leaf, which developed under salt stress, did not change significantly in SR03 and SR12 whereas significant reductions were observed in cv. Pioneer 3906 and SR13. Concentrations of assimilates (i.e. glucose, fructose and sucrose) in the shoot sap were significantly greater under salt stress in SR03 and SR12. However, the greater assimilate supply was not responsible for their salt resistance as there were no significant reductions in assimilate concentrations even in the other two genotypes. Shoot turgor and growth were maintained in SR03 and SR12 at 100 mM Na+ through significant increases in osmolality of the shoot sap. Concentrations of free ABA and ABA-glucose esters (ABA-GE) in the growing region of the fourth leaf increased significantly under salt stress in all genotypes. Leaf area at 100 mM Na(+), expressed as a percentage of that at 1 mM, showed significant positive relationships with free ABA (R(2) = 0.62) and the sum of free ABA and ABA-GE (R(2) = 0.65). Results of this study indicate clearly that a combination of partial osmotic adjustment, a possible reduction of the sensitivity of leaf growth under salt stress to increased ABA concentrations and a growth-promoting function regulated by ABA is responsible for salt resistance in the first phase of salt stress. Genotypic variation in these mechanisms can be utilized to breed salt-resistant genotypes in maize.


Assuntos
Ácido Abscísico/metabolismo , Cloreto de Sódio/farmacologia , Zea mays/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genótipo , Hibridização Genética , Íons/metabolismo , Pressão Osmótica , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/genética , Folhas de Planta/metabolismo , Brotos de Planta/efeitos dos fármacos , Brotos de Planta/genética , Brotos de Planta/metabolismo , Sódio/metabolismo , Zea mays/genética , Zea mays/metabolismo
18.
Funct Plant Biol ; 34(3): 237-245, 2007 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32689350

RESUMO

Facultative plant hemiparasites exhibit optimal growth only when attached to a suitable host. After attachment, stomata of the parasite remain continuously open, thus, optimising the extraction of host xylem sap. When the host shoot was removed from the hemiparasitic Rhinanthus/barley association ~14 days after attachment, the resulting host-free attached Rhinanthus continued to grow and develop similarly well as the attached parasites. These plants, however, showed altered stomatal behaviour: their stomata were open at daytime and closed at night, whereas parasitising Rhinanthus has continuously open stomata all day and night and unattached single Rhinanthus has practically closed stomata throughout day and night. After removal of the host the root growth was strongly increased, thereby increasing the root-to-shoot ratio. Abscisic acid and cytokinin relationships became more 'normal' with the Rhinanthus roots becoming able to synthesise zeatin nucleotides and zeatin ribosides, thus, behaving much as non-parasitic plants in general. It is suggested that the degrading root system of the host plant produces signals that trigger this conversion. Two explanations for these changes are discussed, the supply of dissolved organic nitrogen by the degrading host root system and a possible strong growth of growth promoting soil microorganisms using the degrading host root system as a substrate.

19.
Cell ; 126(6): 1109-20, 2006 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-16990135

RESUMO

Abscisic acid (ABA) is a phytohormone critical for plant growth, development, and adaptation to various stress conditions. Plants have to adjust ABA levels constantly to respond to changing physiological and environmental conditions. To date, the mechanisms for fine-tuning ABA levels remain elusive. Here we report that AtBG1, a beta-glucosidase, hydrolyzes glucose-conjugated, biologically inactive ABA to produce active ABA. Loss of AtBG1 causes defective stomatal movement, early germination, abiotic stress-sensitive phenotypes, and lower ABA levels, whereas plants with ectopic AtBG1 accumulate higher ABA levels and display enhanced tolerance to abiotic stress. Dehydration rapidly induces polymerization of AtBG1, resulting in a 4-fold increase in enzymatic activity. Furthermore, diurnal increases in ABA levels are attributable to polymerization-mediated AtBG1 activation. We propose that the activation of inactive ABA pools by polymerized AtBG1 is a mechanism by which plants rapidly adjust ABA levels and respond to changing environmental cues.


Assuntos
Ácido Abscísico/biossíntese , Arabidopsis/fisiologia , Ativação Enzimática/fisiologia , beta-Glucosidase/metabolismo , Adaptação Fisiológica/fisiologia , Arabidopsis/enzimologia , Arabidopsis/genética , Ritmo Circadiano/fisiologia , Desidratação/enzimologia , Meio Ambiente , Plantas Geneticamente Modificadas/enzimologia , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/fisiologia , Polímeros/metabolismo , Fatores de Tempo , Regulação para Cima/fisiologia
20.
Plant Cell Environ ; 29(8): 1595-605, 2006 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-16898020

RESUMO

Stomatal openings can be stimulated by light through two signalling pathways. The first pathway is blue light specific and involves phototropins, while the second pathway mediates a response to photosynthetically active radiation (PAR). This second pathway was studied with the use of albino Vicia faba plants and variegated leaves of Chlorophytum comosum. Treatment of V. faba with norflurazon (Nf) inhibits the synthesis of carotenoids and leads to albino leaves with guard cells that lack functional green chloroplasts. Guard cells in albino leaf patches of C. comosum, however, do contain photosynthetically active chloroplasts. Stomata in albino leaf patches of both plants did not respond to red light, although blue light could still induce stomatal opening. This shows that the response to PAR is not functioning in albino leaf patches, even though guard cells of C. comosum harbour chloroplasts. Stomata of Nf-treated plants still responded to CO2 and abscisic acid (ABA). The size of Nf-treated guard cells was increased, but impalement studies with double-barrelled microelectrodes revealed no changes in ion-transport properties at the plasma membrane of guard cells. Blue light could hyperpolarize albino guard cells by triggering outward currents with peak values of 37 pA in albino plants and 51 pA in green control cells. Because of the inhibition of carotenoid biosynthesis, Nf-treated V. faba plants contained only 4% of the ABA content found in green control plants. The ABA dose dependence of anion channel activation in guard cells was shifted in these plants, causing a reduced response to 10 microM ABA. These data show that despite the dramatic changes in physiology caused by Nf, the gross responsiveness of guard cells to blue light, CO2 and ABA remains unaltered. Stomata in albino leaf patches, however, do not respond to PAR, but require photosynthetically active mesophyll cells for this response.


Assuntos
Ácido Abscísico/farmacologia , Dióxido de Carbono/farmacologia , Luz , Fotossíntese/efeitos da radiação , Folhas de Planta/efeitos da radiação , Radiação , Asparagaceae/citologia , Asparagaceae/fisiologia , Asparagaceae/efeitos da radiação , Transporte Biológico/efeitos da radiação , Carotenoides/antagonistas & inibidores , Carotenoides/metabolismo , Membrana Celular/metabolismo , Cloroplastos/efeitos dos fármacos , Cloroplastos/metabolismo , Folhas de Planta/citologia , Folhas de Planta/fisiologia , Piridazinas/farmacologia , Vicia faba/citologia , Vicia faba/fisiologia , Vicia faba/efeitos da radiação
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