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Sand verbenas (Abronia spp., Nyctaginaceae) germinate in response to ethylene
Abstract
Sand verbenas (Abronia spp., Nyctaginaceae) are difficult to germinate in the laboratory. This hinders conservation and restoration efforts for Abronia spp. some of which are rare and others of which have been displaced from dune environments by invasive species and human activities. The possibility that ethylene (supplied as the liquid ethephon) could promote germination was investigated for Abronia fragrans, Abronia maritima, Abronia umbellata, and Abronia villosa. Germination of achenes from which the anthocarp had been removed ranged from 0% to 15% in deionized water and at alternating temperatures of 27/20 °C associated with a 12-h light/12-h dark cycle. For A. maritima and A. umbellata under similar conditions of temperature and light, germination exceeded 90% for all concentrations of ethephon tested (10, 100, and 500 μ mol l−1). The rate of germination was highest at 500 μ mol l−1; however, the radicles were stunted at this concentration. Germination was also promoted by imbibition of the achenes with ripe apple tissue providing evidence that the ethephon effects are due to ethylene. Ethephon treatment (100 μ mol l −1) also significantly increased germination for A. fragrans and A. villosa suggesting that the different species of sand verbena may have similar dormancy mechanisms.
... Abronia villosa is a member of Nyctaginaceae family and it is well known with other names like; hairy sand-verbena. This plant is originally from southwestern United States and northern Mexico and it is usually grown in southern California and Baja coast between February and May [14]. ...
The aim of this study was to evaluate the antibacterial and antifungal activities of eco-friendly synthesized silver nanoparticles. The silver nanoparticles were synthesized by biological method using aqueous extract of Abronia villosa. Synthesis of silver nanoparticles was confirmed by color change and characterized using UV-visible spectroscopy, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), and zeta potential analysis. The SEM analysis revealed the presence of spherical silver nanoparticles of the size range 21 to 33 nm. Synthesized silver nanoparticles were used to evaluate their antibacterial effects at different concentrations (25, 50, 75 and 100 µg/ml) on gram negative and gram positive bacteria. The biggest halo zone was observed at 75 and 100 µg/ml concentrations of silver nanoparticles against both gram positive and gram negative bacteria. Antifungal activity of biosynthesized silver nanoparticles was evaluated against seven different phytopathogenic fungi. AgNPs showed high inhibition of radial growth toward all tested fungi. The highest inhibition of fungal growth by AgNPs was recorded against Macrophomina phaseolina (86.06±0.92%). Biosynthesized AgNPs using plant extract are a promising to use safety for various biomedical and agricultural applications.
Plant hormones are signaling molecules that are present in small quantities. They act differently depending upon the concentration and environmental conditions. The main plant hormones are auxins such as indole-3-acetic acid (IAA), the gibberellins (GAs), abscisic acid (ABA), cytokinins, and ethylene. The effect of IAA varies with the concentration and the part of the plant where it is applied. Its exact mechanism of action is not completely known, but it is believed that it is involved in the activation of enzymes, which increases the plasticity of the cell walls, thereby increasing the cell volume and, consequently, the growth of the plant. The GAs are a large family of diterpenes, an important group of plant hormones, which exert several effects on the growth and development of plants, such as germination, growth of leaves, and flower development. Auxins stimulate the transfer activity of the vascular system, causing increased formation of xylem and phloem in woody plants. ABA is associated with the seed maturation and desiccation tolerance of viviparity. Cytokinins, such as zeatin, promote cell division and differentiation of organs, having widely used in the culture and handling plant tissue in vitro. It is also important to cite the ethylene, a gaseous hormone that stimulates fruit ripening, abscission, senescence, and, for some species, flowering. Considering the great importance of agriculture to the global economy, the demand for alternatives to the increase production of various agricultural products is justified. Plant hormones (phytohormones) appear then to increase the technical and economic efficiency of various agricultural production systems. Thus, this chapter focuses on plant hormones and phytochemicals, their structure, mode of action, and its great economic importance for agriculture as well as alternatives that enable their production and use on a large scale.
Abronia macrocarpa is endemic to Texas and it is listed as endangered by federal and state agencies, but it is believed to have a high potential for recovery. Reintroduction is a potential option for recovery of this species and this could be accomplished using seeds planted in the field or transplanting individuals produced ex situ from seeds. We used a split-plot design to determine the percentage of seeds germinating in the field and to test effects of planting seeds in spring versus autumn. Season of planting significantly influenced percentage of germination. Seeds planted in spring (April 2005) exhibited 27.8% germination, while germination of seeds planted in autumn (November 2005) was only 0.8%. We also investigated the induction of seed germination in the laboratory. Difference in germination was 0–68.6% between the control and treatments. Combining scarification then warm stratification followed by cold stratification resulted in significantly higher germination than other treatments.
Pink sandverbena (Abronia umbellata ssp. breviflora) is an endangered plant of Pacific Coast beaches. Restoration efforts have focused on the development of seed germination and field propagation techniques. Germination in the laboratory was highest when seeds were removed from the fruit and received alternating temperatures (20 o C/30 C) and photoperiods. Benefits from cold stratification differed strongly from site to site and year to year. Field-sowing of seeds is also a viable propagation method.
Genetic monitoring of reintroduced plantpopulations can allow assessment of the successin establishing new populations thatgenetically resemble native populations. Weused a PCR-based method (Intersimple SequenceRepeats) to quantify genetic variation in fourreintroduced populations of Abroniaumbellata ssp. breviflora, an annualforb native to the Pacific Coast that isstate-listed endangered in Oregon. Thereintroduced populations ranged in size from 18to 4,111 individuals in the year they weresampled. Genetic variation was also quantifiedin the natural population that served as theseed source for the reintroduction efforts. Atotal of 77 loci (bands) was observed using twoISSR primers, providing 65 polymorphic loci. Asignificant, positive regression was observedbetween the log of population size for the fivepopulations and genetic variation when measuredas percent polymorphic loci (P), expectedheterozygosity (He>
), and with adissimilarity index (1 – Sxy) based on bandsharing. Two of the reintroduced populationsmaintained approximately 90% of the geneticvariation we observed in the source population. Based on these results, we predict thatreintroduced populations of A. u. ssp.breviflora that have at least 1,000individuals should maintain 90% of the geneticvariation of the source population.
The purpose of our research was to determine why seeds of Schoenoplectus hallii germinate only in some wet years. Seeds mature in autumn, at which time they are dormant. Seeds come out of dormancy during winter, if buried in nonflooded, moist soil, but they remain dormant if buried in flooded soil. Nondormant seeds require flooding, light, and exposure to ethylene to germinate. One piece of apple in water (1/12 of an apple in 125 mL of water in a glass jar for a depth of 5 cm) or a 1-μmol/L solution of ethephon elicited very similar (high) germination percentages and vigor of seedlings. Apple, which was shown to produce ethylene in the air space of the jar, was used in a series of experiments to better understand germination. Seeds germinated to 72% if apple was removed from the water after 1 d of incubation, and they germinated to 97% if seeds were washed and placed in fresh water after 3 d of exposure to apple. No seeds germinated in control with no apple. Seeds incubated in apple leachate for 5 d and then transferred to filter paper moistened with distilled water germinated to 90%. Minimum depth of flooding in apple leachate (no soil in jars) for optimum germination was ≥3 cm. Buried seeds of S. hallii exhibited an annual conditional dormancy/nondormancy cycle. Regardless of the month in which seeds were exhumed, they germinated to 59-100% in light in water with apple at daily alternating temperature regimes of 25°/15°, 30°/15°, and 35°/20°C, but germination at 20°/10°C (and to some extent at 15°/6°C) tended to peak in autumn to spring. Thus, seeds can germinate throughout the summer if flooded (ethylene production) and exposed to light. An ethylene cue for germination serves as a "flood-detecting" mechanism and may serve as an indirect signal that water is available for completion of the life cycle and competing species are absent.
The effect of supraoptimal temperatures (30 degrees C, 35 degrees C) on germination and ethylene production of Cicer arietinum (chick-pea) seeds was measured. Compared with a 25 degrees C control, these temperatures inhibited both germination and ethylene production. The effect of supraoptimal temperatures could be alleviated by treating the seeds with ethylene. It was concluded that one effect of high temperature on germination was due to its negative effect on ethylene production. This inhibitory effect of high temperature was due to increased conjugation of 1-aminocyclopropane-1-carboxylic acid to 1-(malonylamino)cyclopropane-1-carboxylic acid and to an inhibition of ethylene-forming enzyme activity.
Abronia macrocarpa, large-fruited sand verbena, is an endangered Texas endemic. A previous study showed that flowers of A. macrocarpa experimentally self-pollinated do not produce seed; only cross-pollination leads to successful seed set. This study examined the selfing barrier. Flowers were experimentally self- and outcrossed, then pollen germination and relative growth of pollen tubes were examined using fluorescent microscopy. Self- and cross-pollen readily adhered to the stigma and germinated forming pollen tubes. Initial rates of pollen tube growth were similar for self- and cross-pollen. However, growth of self-pollen tubes was arrested and the tubes did not penetrate the stigma. Failure to set seed following self-pollination is the result of a pre-fertilization barrier. The inability of self-pollen tubes to penetrate the stigma, presence of trinucleate pollen, and a dry stigma provide evidence suggesting that the self-incompatibility system is likely to be sporophytic.
High O2 tensions, CO4, C2H4 and high temperatures were effective not only in breaking the dormancy of cocklebur (Xanthium pennsylvanicum Wallr.) seeds but also in increasing the germination potential of the nondormant but small seeds. There were few qualitative differences in response to these factors between the dormant and impotent seeds. Unlike CO2, however, enriched O2 and C2H4 were stimulative even at the low temperature of 13°C.
Germination induced by CO2, C2H4 and high temperature treatments was lowered when endogenously evolved C2H4 or CO2 was removed, whereas the effect of O2 enrichment was not affected by their removal. CO2 and high temperatures remarkably stimulated C2H4 production, whereas O2 enrichment had no such effect.
C2H4 productivity was lower in the dormant than non-dormant seeds, suggesting that the after-ripening is characterized by increasing C2H4 production.
1. One temperature shift from 20 to 30 degrees C in darkness induces 30-40% germination in Rumex obtusifolius seeds. The same germination percentages are found with heat treatment varying between 1 and 6 h duration, indicating that the total heat sum of the temperature shift is not important. 2. Germination is greatly enhanced by three consecutive heat shifts of 1 h at 30 degrees C separated by 1 h periods at 20 degrees C. 3. The seeds are activated to a small extent after a slow warming (+2 degrees C h(-1)) from 20 to 30 degrees C, followed by incubation for 1 h at 30 degrees C. Germination is much higher after rapid heating (+10 degrees C h(-1)) to 30 degrees C, followed by Ih incubation at this temperature. Repeated fast heating treatments on four consecutive days enhances germination. Moderately rapid heatings (+3.3 degrees C h(-1)) give intermediate results. 4. The rate of cooling does not influence the germination percentage. Cooling alone cannot induce germination. 5. Heating alone from 15 to 25 degrees C without cooling also activates germination. In this temperature range the seeds are more activated by rapid warming than by slow warming. 6. The ecological relevance of the response to different warming rate is discussed. The insensitivity of seeds to a slow warming might keep deeply buried seeds in a dormant stage.
Plants other than grasses constitute an important part of the native grasslands of North America. Most of these are forbs, a few are shrubs and half-shrubs. Probably 85 to 90 percent of the forbs are perennial and most are as deeply rooted and many far more deeply rooted than the grasses. Their number varies considerably from place to place. In the prairie of the central part of the North American Lowland and on the hard lands and sandy soils of the Great Plains they compose, perhaps, between 5 and 15 percent of the vegetation. They are least abundant in the drier habitats. A recent summary of the community root habits of grasses and an interpretation of the findings included a discussion of soils and climate of each of these extensive areas (Weaver 1958). Hence this need not be repeated here. Suffice it to say that in mixed prairie westward the drier air and decreased water content of soil become limiting factors for growth. Forbs decrease gradually in number, size of individuals, and in the extent of their groupings in societies. This condition prevails despite the fact that the more mesic species of prairie are largely replaced by more xerophytic ones of the Great Plains.
An analysis of the variation patterns in the three Pacific Coast maritime species ofAbronia (Nyctaginaceae) based on 95 population studies, is presented in the form of scatter diagrams. The relationship of this group
of species to other members of the genus, such asA. gracilis Benth., is considered. Despite widespread evidence of hybridization and introgression, the three maritime species (A. latifolia Eschsch.,A. maritima Nutt. ex S. Wats., andA. umbellata Lam.) maintain their distinctness. Most of the taxonomic segregants in this group have been based on what appear to be hybrid
or introgressed individuals, many of which closely resemble members of a series of artificial hybrids made in the greenhouse.
The chromosome number of all three species is estimated as 2n = ca. 46. The species are shown to differ markedly in ecological preference:A. latifolia competing successfully on stable areas of dunes from Vancouver Island, British Columbia, to Santa Barbara Co., California;A. maritima being the major foredune former along the strand from San Luis Obispo Co., California, south to Nayarit, Mexico; andA. umbellata occurring on more stable dunes from San Luis Obispo to San Diego Co., California, and sporadically north and south of this
area. The latter species is pollinated chiefly by nocturnal insects and is fragrant in the evening, whereas the other two
have diurnal flowers. One widespread and two rarer, more northern subspecies ofA. umbellata are recognized in the taxonomic revision, while the other two species are not subdivided taxonomically.
The synthesis and action of ethylene are absolute requirements for seed germination in Cyclopia intermedia (resprouter) and C. subternata (seeder). Stratification at 2 °C in the dark resulted in the breaking of dormancy in the resprouter and the stimulation of the initial rate of germination in the seeder. The dormancy-breaking effect of low temperatures could be substituted for by treatment with ethylene, GA3 or BA. However, in the seeder, only ethylene could mimic the effect of stratification on the rate of seed germination. Inhibition of ethylene action by NBD inhibited the dormancy-breaking effect of stratification, ethylene, GA3 and BA in the resprouter and suppressed germination in the seeder to the levels of the resprouter. Stratification or treatment with GA3 and BA resulted in the suppression of ethylene production due to the suppression of the conversion of ACC to ethylene. The results of this study indicate that the effects of stratification, GA3 and BA on dormancy-breaking and germination could be ascribed to the effects of these treatments on the ability of the seeds to react to ethylene.
Preliminary research indicates that treating arrow-leaved balsamroot (Balsamorhiza sagittata (Pursh) Nutt. [Asteraceae]) seeds with ethylene before stratification increases germination without affecting seedling morphology. Arrow-leaved balsamroot is one of the most dominant forbs in sagebrush and grassland ecosystems of the Interior Plateau of northwest North America. Widely used as a food and medicinal plant by indigenous peoples of this region, this plant has shown in recent research that it has potential as a medicinal herb, as a source of inulin, for ecological restoration purposes, and in horticulture. The significance of this species in native ecosystems and the difficulty inherent in wild harvesting of balsamroot identifies it as a candidate for crop development to meet future needs. Improving germination is the first step to meeting the objectives of economic development in First Nations communities and for environmental conservation.
Genetic variation was evaluated in the federally endangered species Abronia macrocarpa(large-fruited sand-verbena), an herbaceous perennial restricted to deep sandy soils and endemic to three counties of east-central Texas. Seven of the ten known populations were sampled and analyzed using starch gel electrophoresis of eight enzymes coded by 18 interpretable loci. Duplicate gene expression was observed for four loci, suggesting polyploid ancestry for the lineage that includes A. macrocarpa. Values for estimators of genetic polymorphism within populations (ranges: P 5 38.9%-61.1%, A 5 1.7-2.1, H 5 0.122-0.279) exceeded average values for seed plants (P 5 34.2%, A 5 1.53, H 5 0.113). Genotype proportions at most loci in most populations were in Hardy-Weinberg equilibrium, consistent with obligate outcrossing previously docu- mented for this species; exceptions could be attributed to population substructure. Values of FST tended to be high, ranging from 0.021 to 0.481 for individual loci (mean FST 5 0.272), indicating substantial divergence and limited gene flow among populations, despite their close geographic proximity. Pairwise values of Nei's genetic identity between populations ranged from 0.799 to 0.975 and tended to be influenced by geographic proximity of population pairs. Collectively, these data suggest a long history of isolation among populations that have not been subjected to bottlenecks. Isolation of A. macrocarpa populations apparently results from the disjunct occurrence of suitable habitat and perhaps has been accentuated by human disturbance.
We examined the breeding system, reproductive output and pollination ecology of Abronia ammophila Greene, a rare and highly restricted endemic of Yellowstone National Park, Wyoming, USA. Floral morphology permits the automatic deposition of self-pollen on the stigma of individual flowers, and male and female reproductive functions temporally overlap. In controlled hand-pollination treatments, we found no significant difference among pollination treatments (unmanipulated, self-pollinated or cross-pollination). The species maintains a long reproductive season with high reproductive output (natural seed set ranged from 59 to 84%). Our results, along with pollinator observations, suggest that A. ammophila exhibits a mixed-mating system: the species can produce seed without pollinators (via either autogamy or agamospermy), but is also visited by an array of pollinating insects that included moths, butterflies and bumblebees. However, noctuid moths were the most abundant pollinators. In contrast, other Abronia species are obligate outcrossers. The mixed-mating system of A. ammophila may have evolved as a consequence of ecological pressures such as scarcity of mates or pollinators.
1. One temperature shift from 20 to 30°C in darkness induces 30–40% germination in Rumex obtusifolius seeds. The same germination percentages are found with heat treatment varying between 1 and 6h duration, indicating that the total heat sum of the temperature shift is not important.
2. Germination is greatly enhanced by three consecutive heat shifts of 1h at 30°C separated by 1h periods at 20°C.
3. The seeds are activated to a small extent after a slow warming (+2°Ch–1) from 20 to 30°C, followed by incubation for 1h at 30°C. Germination is much higher after rapid heating (+10°Ch–1) to 30°C, followed by 1h incubation at this temperature. Repeated fast heating treatments on four consecutive days enhances germination. Moderately rapid heatings (+3·3°Ch–1) give intermediate results.
4. The rate of cooling does not influence the germination percentage. Cooling alone cannot induce germination.
5. Heating alone from 15 to 25°C without cooling also activates germination. In this temperature range the seeds are more activated by rapid warming than by slow warming.
6. The ecological relevance of the response to different warming rate is discussed. The insensitivity of seeds to a slow warming might keep deeply buried seeds in a dormant stage.
Differences in inflorescence maturation patterns, in the scar at the apex of the anthocarp after abscission of the upper portion
of the perianth, and between receptacles give additional support for the recognition ofAbronia andTripterocalyx as separate genera. Keys, descriptions, and distribution of 11 species ofAbronia and three species ofTripterocalyx are given.
Cumulative germination percentages for (A) Abronia maritima and (B) Abronia umbellata imbibed in deionized water in the presence or absence of a slice of ripe apple. Bar represents the maximum LSD
- Article In
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ARTICLE IN PRESS Fig. 2. Cumulative germination percentages for (A) Abronia maritima and (B) Abronia umbellata imbibed in deionized water in the presence or absence of a slice of ripe apple. Bar represents the maximum LSD (P ¼ 0.05).
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