RESUMEN

According to the Cholodny-Went hypothesis, gravitropic differential growth is brought about by the redistribution of auxin (indolyl-3-acetic acid, IAA). We reinvestigated the relevance of different auxins and studied the role of ethylene in hypocotyls of sunflower and shoots and roots of rye and maize seedlings. Incubation of coleoptiles and of sunflower hypocotyls in solutions of IAA and dichlorophenoxyacetic acid as well as naphthylacetic acid resulted in a two- to threefold length increase compared to water controls. In spite of this pronounced general effect on elongation growth, gravi-curvature was similar to water controls. In contrast to this, inhibition of ethylene synthesis by aminoethoxyvinylglycine prevented differential growth of both hypocotyls and coleoptiles and of roots of maize. In horizontally stimulated maize roots growing on surfaces, inhibition of ethylene perception by methylcyclopropene inhibited roots to adapt growth to the surface, resulting in a lasting vertical orientation of the root tips. This effect is accompanied by up- and down-regulation of a number of proteins as detected by two-dimensional matrix-assisted laser desorption-ionization time-of-flight mass spectrometry. Together the data query the regulatory relevance of IAA redistribution for gravitropic differential growth. They corroborate the crucial regulatory role of ethylene for gravitropic differential growth, both in roots and coleoptiles of maize as well as in hypocotyls.

Asunto(s)

Etilenos/metabolismo , Gravitropismo , Helianthus/crecimiento & desarrollo , Secale/crecimiento & desarrollo , Zea mays/crecimiento & desarrollo , Ácido 2,4-Diclorofenoxiacético/farmacología , Cotiledón/crecimiento & desarrollo , Cotiledón/metabolismo , Ciclopropanos/farmacología , Enzimas/metabolismo , Glicina/análogos & derivados , Glicina/farmacología , Gravitropismo/efectos de los fármacos , Helianthus/efectos de los fármacos , Helianthus/metabolismo , Herbicidas/farmacología , Hipocótilo/crecimiento & desarrollo , Hipocótilo/metabolismo , Ácidos Indolacéticos/farmacología , Modelos Biológicos , Ácidos Naftalenoacéticos/farmacología , Mapeo Peptídico , Reguladores del Crecimiento de las Plantas/farmacología , Proteínas de Plantas/metabolismo , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Secale/efectos de los fármacos , Secale/metabolismo , Espectrometría de Masa por Láser de Matriz Asistida de Ionización Desorción , Factores de Tiempo , Zea mays/efectos de los fármacos , Zea mays/metabolismo

RESUMEN

Marine macrolides latrunculins are highly specific toxins which effectively depolymerize actin filaments (generally F-actin) in all eukaryotic cells. We show that latrunculin B is effective on diverse cell types in higher plants and describe the use of this drug in probing F-actin-dependent growth and in plant development-related processes. In contrast to other eukaryotic organisms, cell divisions occurs in plant cells devoid of all actin filaments. However, the alignment of the division planes is often distorted. In addition to cell division, postembryonic development and morphogenesis also continue in the absence of F-actin. These experimental data suggest that F-actin is of little importance in the morphogenesis of higher plants, and that plants can develop more or less normally without F-actin. In contrast, F-actin turns out to be essential for cell elongation. When latrunculin B was added during germination, morphologically normal Arabidopsis and rye seedlings developed but, as a result of the absence of cell elongation, these were stunted, resembling either genetic dwarfs or environmental bonsai plants. In conclusion, F-actin is essential for the plant cell elongation, while this F-actin-dependent cell elongation is not an essential feature of plant-specific developmental programs.

Asunto(s)

Actinas/fisiología , Compuestos Bicíclicos Heterocíclicos con Puentes/farmacología , Plantas/efectos de los fármacos , Tiazoles/farmacología , División Celular/efectos de los fármacos , Ácidos Indolacéticos/farmacología , Mitosis , Desarrollo de la Planta , Tiazolidinas

RESUMEN

Differential growth of the nodal regions of graviresponding Tradescantia fluminensis (Wandering Jew) was analysed with special respect to the extension-restricting epidermal cells of the opposite growing and growth-inhibited organ flanks. Gravicurvature of horizontally gravistimulated isolated nodes depends on auxin (indolyl-3-acetic acid, IAA) and shows a node-specific profile in which the third node below the tip showed the greatest response. Exogenously supplied gibberellic acid induced no gravitropic growth. Vertically oriented isolated nodes supplied with exogenous IAA showed, on an electron microscopical level, conspicuous membrane invaginations with adjacent wall depositions restricted to the outer tangential epidermal cell walls. Their number was more than doubled by exogenously supplied Ca2+, which inhibited IAA-induced growth. No such changes could be detected in water-incubated segments or inner tissues of IAA-supplied segments. Gravistimulated differential growth of nodes of intact shoots and of nodal segments was characterized by changes similar to the ones induced by exogenous IAA, with greatly increased numbers of wall depositions within the epidermal cells of the growth-inhibited upper organ flank. Similar to the gravistimulated wall depositions, an asymmetric distribution pattern of Ca2+ was detected in the epidermal cell walls employing x-ray energy spectrum analysis (EDX). The results indicate that growth of nodes of Tradescantia fluminensis is regulated via IAA-induced secretion and subsequent infiltration of wall components enabling wall extension. The data support the hypothesis that temporary differential growth during gravicurvature of Tradescantia fluminensis is mediated by the antagonistic effect of Ca(2+)-ions on the infiltration of IAA-induced wall-loosening components into the outer, extension-restricting epidermal walls thereby inhibiting growth.

Asunto(s)

Gravitropismo , Ácidos Indolacéticos/metabolismo , Magnoliopsida/crecimiento & desarrollo , Periplasma/metabolismo , Epidermis de la Planta/crecimiento & desarrollo , Calcio/metabolismo , Calcio/farmacología , Pared Celular/metabolismo , Giberelinas/metabolismo , Giberelinas/farmacología , Ácidos Indolacéticos/farmacología , Magnoliopsida/metabolismo , Magnoliopsida/ultraestructura , Microscopía Electrónica de Rastreo , Epidermis de la Planta/metabolismo , Epidermis de la Planta/ultraestructura , Reguladores del Crecimiento de las Plantas/metabolismo , Reguladores del Crecimiento de las Plantas/farmacología

RESUMEN

Subsequent to inversion, horizontally pre-gravistimulated coleoptiles exhibit an increased gravicurvature capacity as compared to vertically pre-gravistimulated and subsequently horizontally gravistimulated coleoptiles. This indicates that gravistimulated inhibition of growth of the upper organ flank during gravicurvature is mediated via the retention of wall loosening potential. After inversion, this potential contributes to enhanced cell extension on the then physiologically lower side.

Asunto(s)

Pared Celular/fisiología , Cotiledón/crecimiento & desarrollo , Gravitropismo/fisiología , Secale/crecimiento & desarrollo , Cotiledón/citología , Cotiledón/metabolismo , Gravitación , Ácidos Indolacéticos/metabolismo , Periplasma/fisiología , Epidermis de la Planta/citología , Epidermis de la Planta/fisiología , Reguladores del Crecimiento de las Plantas/metabolismo , Secale/citología , Secale/metabolismo

RESUMEN

Gravitropic plant growth is due to gravistimulated asymmetric extension rates of the affected flanks of the graviresponding organ. Differential growth of the upper and lower flanks (UFs, LFs) of graviresponding plant organs may in principle be achieved by various biochemical and/or biophysical asymmetries. The gravistimulated mechanism(s) by which the different growth rates are determined is still unresolved, as is the mechanism of IAA-regulated growth. The purpose of this brief review is to summarize and critically evaluate data concerning gravistimulated asymmetries, especially with respect to the interface of the plasma membranes and of the extension-restricting, load-bearing epidermal cell walls (Masuda and Yamamoto 1972 Physiol Plant 27:109-115). In addition, recent results obtained by the author in experiments with rye coleoptiles will be presented and discussed in the context of a tentative model of gravistimulated wall asymmetries temporarily causing differential growth.

Asunto(s)

Gravitropismo/fisiología , Ácidos Indolacéticos/metabolismo , Epidermis de la Planta/citología , Epidermis de la Planta/ultraestructura , Reguladores del Crecimiento de las Plantas/metabolismo , Fenómenos Fisiológicos de las Plantas , Fenómenos Biofísicos , Biofisica , Calcio/metabolismo , Pared Celular/fisiología , Cotiledón/citología , Cotiledón/crecimiento & desarrollo , Cotiledón/ultraestructura , Electrofisiología , Epidermis de la Planta/crecimiento & desarrollo , Protones

RESUMEN

Surgical removal of the coleoptiles from germinating seedlings of Secale cereale L., Avena sativa L., and Zea mays L. leads to a total loss of gravitropic response of the shoot without affecting growth. The principal function of coleoptiles is therefore to guide the gravi-insensitive shoot to the soil surface.

Asunto(s)

Avena/crecimiento & desarrollo , Cotiledón/fisiología , Sensación de Gravedad/fisiología , Secale/crecimiento & desarrollo , Zea mays/crecimiento & desarrollo , Avena/fisiología , Cotiledón/crecimiento & desarrollo , Fenómenos Fisiológicos de las Plantas , Brotes de la Planta/crecimiento & desarrollo , Brotes de la Planta/metabolismo , Brotes de la Planta/fisiología , Secale/fisiología , Zea mays/fisiología

RESUMEN

In various studies, auxin (IAA)-induced coleoptile growth has been reported to be closely correlated with an increased occurrence of osmiophilic particles (OPs) at the inner surface of the outer, growth-limiting epidermal cell wall, indicating a possible function related to the mechanism of IAA-induced wall loosening. In order to test whether changes in cell elongation rates of upper and lower flanks (UFs, LFs, respectively) during graviresponsive growth are reflected in appropriate changes in the occurrence of OPs, rye (Secale cereale L.) coleoptiles either as segments or as part of intact seedlings, were gravitropically stimulated by positioning them horizontally for 2 h. Ultrastructural analyses within the UFs and LFs of the upward-bending coleoptiles revealed a distinct imbalance in the occurrence of OPs. The number of OPs per transverse epidermal cell section of the elongation-inhibited UF on average amounted to twice the number of OPs counted in epidermal cell sections of the faster-growing LF. As a hypothesis, the results lead us to suggest that OPs are involved in the mechanism of wall loosening and that temporary growth inhibition of epidermal cells of the UF during upward bending is mediated by inhibition of OP entry into the cell walls. Thereby, more OPs accumulate near the inner surface of the outer wall of epidermal cells of the UF compared with the LF.

Asunto(s)

Cotiledón/crecimiento & desarrollo , Cotiledón/ultraestructura , Gravitación , Gravitropismo/fisiología , Epidermis de la Planta/ultraestructura , Secale/ultraestructura , Pared Celular/ultraestructura , Cotiledón/metabolismo , Ácidos Indolacéticos/metabolismo , Microscopía Electrónica , Concentración Osmolar , Epidermis de la Planta/crecimiento & desarrollo , Reguladores del Crecimiento de las Plantas/metabolismo , Secale/crecimiento & desarrollo , Secale/metabolismo

RESUMEN

2,6-Dichlorobenzonitrile (DCB, 100 mum) inhibited by 80 to 85% the incorporation of [(3)H]glucose into cellulose in stem segments of etiolated pea (Pisum sativum) seedlings. The inhibition lasted for at least 24 h. In the period 1 to 4 h after the excision of the segments, DCB did not influence elongation in the presence or absence of 2,4-dichlorophenoxyacetic acid (2,4-D). However, during the period 1 to 24 h after excision, DCB enhanced endogenous and 2,4-D-stimulated elongation by 65 and 34%, respectively. DCB did not affect the incorporation of (3)H from [(3)H]arabinose into xyloglucan, and did not change the ability of the [(3)H]xyloglucan formed in vivo to bind strongly to the cell wall. Therefore, at least 80 to 85% of newly synthesized cellulose was excess to the requirements for tight wall binding of newly synthesized xyloglucan. This conflicts with the hypothesis that xyloglucan is held in the cell wall solely by direct hydrogen bonding to the surfaces of cellulosic microfibrils.