Effects of Previous Pollination and Stylar Ethylene on Pollen Tube Growth in Petunia hybrida Styles

The effect of ethylene on the growth rate of pollen tubes in styles of Petunia hybrida was examined. Apart from its strong inhibition of pollination-induced ethylene synthesis, aminoethoxyvinylglycine, placed on the stigma, did not impede tube growth. The inhibitors of the action of ethylene, silver thiosulfate and 2,5-norbornadiene, were similarly ineffective. Application of the ethylene precursor, 1-amino-cyclopropane-1-carboxylic acid, onto the stigma at different intervals prior to pollination evoked synthesis of ethylene, but was without effect on tube growth. However, prepollination (by 24 hours) with Nicotiana tabacum pollen, significantly enhanced tube growth of Petunia pollen. This enhancement was not counteracted by the pretreatment of stigmas with aminoethoxy-vinylglycine. It is concluded that the ethylene associated with pollination is without effect on pollen tube growth in the style, but that other pollination-induced factors may lead to an acceleration of growth.     

Ethylene is differentially regulated during sugar beet germination and affects early root growth in a dose-dependent manner

Main conclusion

By integrating molecular, biochemical, and physiological data, ethylene biosynthesis in sugar beet was shown to be differentially regulated, affecting root elongation in a concentration-dependent manner. There is a close relation between ethylene production and seedling growth of sugar beet (Beta vulgaris L.), yet the exact function of ethylene during this early developmental stage is still unclear. While ethylene is mostly considered to be a root growth inhibitor, we found that external 1-aminocyclopropane-1-carboxylic acid (ACC) regulates root growth in sugar beet in a concentration-dependent manner: low concentrations stimulate root growth while high concentrations inhibit root growth. These results reveal that ethylene action during root elongation is strongly concentration dependent. Furthermore our detailed study of ethylene biosynthesis kinetics revealed a very strict gene regulation pattern of ACC synthase (ACS) and ACC oxidase (ACO), in which ACS is the rate liming step during sugar beet seedling development.     

Role of ethylene and cytokinins in the initiation of lateral shoot growth in bromeliads

Aechmea victoriana var discolor L. B. Foster and Aechmea dactylina Bal. are commercially propagated in vitro through lateral shoot growth. A modified Murashige and Skoog medium is used which contains both BA and IAA. These growth substances were shown in the present study to synergistically stimulate the production of ethylene by the cultured plants. The stimulation of ethylene production is correlated with the outgrowth of the lateral buds. The rise in ethylene production was concluded to induce lateral shoot growth, because: (a) outgrowth of the shoots was blocked by preventing an increase in ethylene production, (b) 1-aminocyclopropane-1-carboxylic acid (ACC), the natural precursor of ethylene biosynthesis, substituted for IAA in the promotion of ethylene production and lateral bud outgrowth. Although ACC could substitute for IAA, it could not substitute for BA; therefore, cytokinins are concluded to be essential for lateral bud outgrowth in vitro in Aechmea. These results suggest that cytokinins and ethylene both play roles in natural lateral bud initiation and that the cytokinin function involves two stages of the process.     

Auxin stimulation of ethylene evolution

The stimulation of ethylene production from seedling tissue of Phascolus vulgaris, Helianthus annuus and Zea mays by growth regulators was inhibited by actinomycin D and puromycin and to a lesser extent by 2-thiouracil and p-fluorophenylalanine. It is concluded that the mechanism of action of growth regulators on the enhancement of ethylene production is the formation of enzymes involved in ethylene biogenesis.     

Ethylene Production by Plant Cell Cultures: Variations in Production during Growing Cycle and in Different Plant Species

Suspension cultures of Rosa sp., soybean (Glycine max L.), wheat (Triticum monococcum L.), sweet clover (Melilotus alba Desc.), Haplopappus gracilis Nutt., and rue (Ruta graveolens) produced ethylene. The amount varied with the species. The rate of formation in rose and Haplopappus cells paralleled growth but accelerated when the stationary phase was reached, after which the rate declined sharply. Light was not required for ethylene production. Exogenous ethylene could not replace 2,4-dichlorophenoxyacetic acid or naphthalineacetic acid in the cell cultures, and there was no stimulation of growth in the normal medium. Ethylene at 20 mm reduced growth of Ruta and rose cells by 30 and 20%, respectively. The amounts of ethylene produced by the cultures do not affect growth.     

Characterization of an Ethylene Overproducing Mutant of Tomato (Lycopersicon esculentum Mill. Cultivar VFN8)

Ethylene production rates and tissue ethylene concentrations were determined for the single-gene, Epinastic (Epi) tomato (Lycopersicon esculentum Mill.) mutant, and its parent, cv VFN8. The Epi phenotype was characterized by severe leaf epinasty, thickened stems and petioles, and a compact growth habit. In 4-day-old seedlings, ethylene production was significantly higher in Epi than in VFN8. Ethylene production rates also were higher for excised root, hypocotyl, cotyledon, and shoot tissue of 14-day-old Epi seedlings as compared with VFN8. The greatest difference in the ethylene production rate was observed in excised Epi shoot tissue, which was more than 2.5 times higher than in VFN8. Tissue ethylene concentrations of 19−, 25−, and 31-day-old Epi plants were 8, 172, and 307% higher than for VFN8, corresponding to increasing expression of the Epi phenotypic characteristics with age. The highest ethylene concentrations occurred in the shoot apex of both genotypes. Higher ethylene concentrations in Epi resulted from greater 1-aminocyclopropane-1-carboxylic acid content rather than increased ethylene-forming enzyme activity. The elevated ethylene levels in Epi did not result from increased auxin sensitivity. The sensitivity of root growth to inhibition by ethylene did not differ between VFN8 and Epi. Although elevated levels of ethylene in Epi plants apparently exacerbate its epinastic growth characteristics, other evidence indicates that this may not be the fundamental lesion. This mutant may provide a unique system for investigating the regulation of ethylene biosynthesis and the role of target cell types in plant development.     

Ethylene Modulates the Developmental Plasticity and the Growth Balance Between Shoot and Root Systems in the In Vitro Grown Epiphytic Orchid Catasetum fimbriatum

The epiphytic habitat is potentially one of the most stressful environments for plants, making the effective developmental control in response to external cues critical for epiphyte survival. Because ethylene mediates several abiotic stresses in plants, here, we have examined the ethylene influence in both shoot and root systems of the epiphytic orchid Catasetum fimbriatum. Under controlled conditions, ethylene production was quantified during an entire growth cycle of C. fimbriatum development in vitro, while treatments modulating either ethylene concentration or perception were carried out over the early growth phase of these plants. After treatments, growth measurements and histological features were studied in both shoot and root tissues. Ethylene production showed a decreasing trend over the period of organ elongation; however, it increased considerably when leaves were shed, and a new axillary bud was initiating. The early exposure of young plants to higher concentrations of ethylene triggered morphogenic responses that included root hair formation instead of velamen, and a combination of inhibitory effects (decreases in both stem enlargement and cellular/organ elongation) and inductive effects (increases in leaf and root formation, bud initiation and cellular thickening) on plant growth, which favored biomass allocation to roots. Conversely, inhibition of ethylene perception over the plant growth phase generally resulted in the opposite morphogenic responses. Our data indicate that periodic variations in ethylene concentration and/or sensitivity seem to modulate several developmental features in shoot and root systems of C. fimbriatum which could have adaptive significance during the growing phase of this epiphytic orchid.     

Auxin and Ethylene Regulation of Petiole Epinasty in Two Developmental Mutants of Tomato, diageotropica and Epinastic

The epinastic growth responses of petioles to auxin and ethylene were quantified in two developmental mutants of tomato (Lycopersicon esculentum Mill.). In the wild type parent line, cultivar VFN8, the epinastic response of excised petiole sections was approximately log-linear between 0.1 and 100 micromolar indole-3-acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D) concentrations, with a greater response to 2,4-D at any concentration. When ethylene synthesis was inhibited by aminoethoxyvinylglycine (AVG), epinasty was no longer induced by auxin, but could be restored by the addition of ethylene gas. In the auxin-insensitive mutant, diageotropica (dgt), no epinastic response to IAA was observed at IAA concentrations that effectively induced epinasty in VFN8. In the absence of added IAA, epinastic growth of dgt petioles in 1.3 microliters per liter exogenous ethylene gas was more than double that of VFN8 petioles. IAA had little additional effect in dgt, but promoted epinasty in VFN8. These results confirm that tomato petiole cells respond directly to ethylene and make it unlikely that the differential growth responsible for epinasty results from lateral auxin redistribution. The second mutant, Epinastic (Epi), exhibits constitutively epinasty, cortical swelling, and root branching symptomatic of possible alternation in auxin or ethylene regulation of growth. Only minor quantitative differences were observed between the epinastic responses to auxin and ethylene of VFN8 and Epi. However, in contrast to VFN8, when ethylene synthesis or action was inhibited in Epi, auxin still induced 40 to 50% of the epinastic response observed in the absence of inhibitors. This indicates that the target cells for epinastic growth in Epi are qualitatively different from those of VFN8, having gained the ability to grow differentially in response to auxin alone. The dgt and Epi mutants provide useful systems in which to study the genetic determination of target cell specificity for hormone action.     

Mechanism of Auxin-induced Ethylene Production

Indoleacetic acid-induced ethylene production and growth in excised segments of etiolated pea shoots (Pisum sativum L. var. Alaska) parallels the free indoleacetic acid level in the tissue which in turn depends upon the rate of indoleacetic acid conjugation and decarboxylation. Both ethylene synthesis and growth require the presence of more than a threshold level of free endogenous indoleacetic acid, but in etiolated tissue the rate of ethylene production saturates at a high concentration and the rate of growth at a lower concentration of indoleacetic acid. Auxin stimulation of ethylene synthesis is not mediated by induction of peroxidase; to the contrary, the products of the auxin action which induce growth and ethylene synthesis are highly labile.     

Ethylene production by plant cell cultures: the effect of auxins, abscisic Acid, and kinetin on ethylene production in suspension cultures of rose and ruta cells

Cell suspension cultures of Ruta graveolens (rue) and Rosa sp. produce ethylene. Both cultures grow at a high rate in hormone-free media. The rose cells are undifferentiated while the Ruta cells differentiate and form shoots after extended culture in hormone-free medium. Addition of 2,4-dichlorophenoxyacetic acid stimulated ethylene production in Ruta cells but not in rose cells. Abscisic acid (ABA) inhibited growth and ethylene production in rose, but only ethylene production in Ruta cells. Addition of kinetin reversed the inhibition by abscisic acid in the rose cells but not in the Ruta cells. The results suggested a distinct physiological difference between the two cultures. The Ruta cells responded to the growth regulators in a manner similar to whole plants.     

Involvement of ethylene in responses of etiolated bean hypocotyl hook to coumarin

Coumarin, at concentrations between 1.0 and 0.1 mm, inhibited red light-induced opening of the etiolated bean hypocotyl hook. In addition, anthocyanin synthesis and geotropic bending were inhibited. Coumarin stimulated ethylene synthesis, and ethylene was shown to mediate the inhibitory actions of coumarin. This conclusion was supported by: (a) the parallel concentration dependence and time sequence of hook closing and ethylene synthesis, (b) the restriction of the bulk of coumarin-induced ethylene production to the curved portion of the hook where opening is expressed, (c) the ability of both coumarin and ethylene to reclose partially opened hooks, and (d) the ability of exogenous ethylene, in the amounts produced by coumarintreated hooks, to duplicate the inhibitory effects of coumarin. There was an increasing stimulation of growth of the straight portion of the hypocotyl hook section as coumarin concentrations were increased from 0.1 to 1.0 mm. This action of coumarin was not duplicated by ethylene and occurred regardless of the presence or absence of added ethylene. The results of this study suggest that many actions of coumarin in growth systems are mediated by ethylene produced in response to the coumarin.     

Abscisic Acid and Ethylene Increase in Heterodera avenae-infected Tolerant or Intolerant Oat Cultivars

The relationship between root stunting caused by the cereal cyst nematode and levels of two root growth inhibiting hormones, abscisic acid and ethylene, was investigated in aseptically cultured root segments and in intact roots of two oat cultivars differing in tolerance to the nematode. Cultured root segments of oat cultivars New Zealand Cape (tolerant) and Sual (intolerant) were inoculated with sterilized Heterodera avenae second-stage juveniles. Suppressed growth of root axes and emerged laterals following nematode penetration corresponded to an increase in abscisic acid and ethylene in roots of both intolerant and tolerant cultivars. When the experiment was repeated on intact root systems, nematodes retarded root growth of Sual more than New Zealand Cape despite an increase in ABA and ethylene in both cultivars. Abscisic acid and (or) ethylene may be involved in growth inhibition of H. avenae-infected roots but appear to play no direct role in determining tolerance.     

Effect of Inhibitors and Stimulators of Ethylene Production on Gall Development in Meloidogyne javanica-Infected Tomato Roots

Excised tomato roots infected with Meloidogyne javanica produced ethylene at 3-6 times the rate of noninfected roots. This increase in ethylene production started 5 days after inoculation. Gall growth and ethylene production in infected roots were accelerated by 1-aminocyclopropane-1-carboxylic acid (ACC), indole acetic acid (IAA), and ethrel known as ethylene production stimulators. When inhibitors of ethylene production, like aminoethoxyvinylglycine (AVG) or aminoxyacetic acid (AOA), or inhibitors of ethylene action like silver thiosulfate (STS), were applied, gall growth and ethylene production were inhibited. Enhanced expansion of parenchymatous cells was observed in sections from nematode-induced galls and ethylene-treated roots. Lignification of xylem elements and fibers in the vascular cylinder was markedly inhibited in the gall, compared with noninfected root tissue. Because ethylene is known to induce cell expansion and to inhibit lignification, it is suggested that this plant hormone plays a major role in the development of M. javanica-induced galls. Ethylene affects gall size by enhancing parenchymatous tissue development and allows expansion of giant cells and the nematode body by reducing tissue lignification.     

Influence of Acetylene on Growth of Sulfate-Respiring Bacteria

At a concentration of 20% of the atmosphere of the culture flasks, acetylene inhibited growth and carbon dioxide production by Desulfovibrio desulfuricans and Desulfovibrio gigas. The bacteria did not reduce acetylene to ethylene, and neither acetylene dicarboxylic acid nor ethylene was inhibitory. At 10%, acetylene was partially inhibitory for the desulfovibrios. At 5%, acetylene impeded the rate but did not limit the extent of growth and catabolism of the desulfovibrios. Desulfotomaculum ruminis was affected only negligibly, if at all, by acetylene and ethylene at any of these concentrations.     

The aux1 Mutation of Arabidopsis Confers Both Auxin and Ethylene Resistance

Mutagenized populations of Arabidopsis thaliana seedlings were screened for plants capable of root growth on inhibitory concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid. Four of the mutant lines recovered from this screen display a defect in root gravitropism as well as hormone resistance. The aerial portions of these plants are similar to wild-type in appearance. Genetic analysis of these four mutants demonstrated that hormone resistance segregated as a recessive trait and that all four mutations were alleles of the auxin-resistant mutation aux1 [Maher HP, Martindale SJB (1980) Biochem Genet 18: 1041-1053]. These new mutants have been designated aux1-7, 1-12, 1-15, and 1-19. The sensitivity of wild-type and aux1-7 roots to indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid, and ethylene was determined. The results of these assays show that aux1-7 plants require a 12-fold (indole-3-acetic acid) or 18-fold (2,4-dichlorophenoxyacetic acid) higher concentration of auxin than wild-type for a 50% inhibition of root growth. In addition, ethylene inhibition of root growth in aux1-7 plants is approximately 30% that of wild-type at saturating ethylene concentrations. These results indicate that aux1 plants are resistant to both auxin and ethylene. We have also determined the effect of ethylene treatment on chlorophyll loss and peroxidase activity in the leaves of aux1 and wild-type plants. No difference between mutant and wild-type plants was observed in these experiments, indicating that hormone resistance in aux1 plants may be limited to root growth. Our studies suggest that the AUX1 gene may have a specific function in the hormonal regulation of gravitropism.     

Interrelationships between Ethylene Production,Gall Formation,and Root-knot Nematode Development in Tomato Plants Infected with Meloidogyne javanica

Ethylene production was determined in excised tomato (Lycopersicon esculentum) root cultures of Meloidogyne javanica susceptible and resistant cultivars infected with M. javanica. Uninfected cultivars produced very low amounts of ethylene. Relatively high amounts of ethylene were produced by the infected susceptible cultivars. Peak production of 1.6 n moles * g root⁻¹ * h¹⁻ occurred between 9 and 16 days after inoculation (DAI). The period of high ethylene production coincided with that of rapid increase in gall weight. Low amounts of ethylene were also released by the infected resistant cultivar between 9 and 12 DAI, which follows the hypersensitivity reaction. Ethylene production in infected intact plants during the period of rapid gall growth was twice as much as in uninfected plants during the same time. Exposing excised root cultures to 0.5 or l0 ppm ethylene accelerated the rate of increase in gall weight of M. javanica infected roots. In contrast, overall root growth was inhibited by these treatments, compared to infected roots which were not exposed to ethylene.     

Inhibitory action of auxin on root elongation not mediated by ethylene

The inhibitory effects of indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylic acid (ACC) on elongation growth of pea (Pisum sativum L.) seedling roots were investigated in relation to the effects of these compounds on ethylene production by the root tips. When added to the growth solution both compounds caused a progressively increasing inhibition of growth within the concentration range of 0.01 to 1 micromolar. However, only ACC increased ethylene production in root tips excised from the treated seedlings after 24 hours. High auxin concentrations caused a transitory increase of ethylene production during a few hours in the beginning of the treatment period, but even in 1 micromolar IAA this increase was too low to have any appreciable effect on growth. ACC, but not IAA, caused growth curvatures, typical of ethylene treatment, in the root tips. IAA caused conspicuous swelling of the root tips while ACC did not. Cobalt and silver ions reversed the growth inhibitory effects induced by ACC but did not counteract the inhibition of elongation or swelling caused by IAA. The growth effects caused by the ACC treatments were obviously due to ethylene production. We found no evidence to indicate that the growth inhibition or swelling caused by IAA is mediated by ethylene. It is concluded that the inhibitory action of IAA on root growth is caused by this auxin per se.