Competition of unsaturated compounds with ethylene for binding and action in plants

The compounds 2,5-norbornadiene, cyclopentadiene, furan, pyrrole, thiophene, 1-methylpyrrole, dicyclopentadiene, methylcyclopentadiene (dimer), and cycloheptatriene have been tested for competition with ethylene for binding and for biological activity using banana fruit. In addition, acetylene, allene, and 1,3-butadiene were tested. All of these compounds competed with ethylene for binding in vitro in a Triton X-100 extract of mung bean sprouts and in vivo in tobacco leaves. Only acetylene, allene, and furan are active in giving an ethylene response in banana. the others all suppress the ethylene response. Only acetylene and allene stimulate ethylene synthesis. Most of the compounds diffuse away from the binding site upon exposure to air.R.J. Reynolds Research Apprentice     

Nonphysiological binding of ethylene by plants

Ethylene binding to seedling tissue of Vicia faba, Phaseolus vulgaris, Glycine max, and Triticum aestivum was demonstrated by determining transit time required for ethylene to move through a glass tube filled with seedling tissue. Transit time for ethylene was greater than that for methane indicating that these tissues had an affinity for ethylene. However, the following observations suggest that the binding was not physiological. Inhibitors of ethylene action such as Ag⁺ ions and CO₂ did not decrease binding. Mushrooms which have no known sites of ethylene action also demonstrated ethylene binding. The binding of acetylene, propylene, ethylene, propane, and ethane more closely followed their solubility in water than any known physiological activity.     

Current methods for detecting ethylene in plants

Background

In view of ethylene''s critical developmental and physiological roles the gaseous hormone remains an active research topic for plant biologists. Progress has been made to understand the ethylene biosynthesis pathway and the mechanisms of perception and action. Still numerous questions need to be answered and findings to be validated. Monitoring gas production will very often complete the picture of any ethylene research topic. Therefore the search for suitable ethylene measuring methods for various plant samples either in the field, greenhouses, laboratories or storage facilities is strongly motivated.

Scope

This review presents an update of the current methods for ethylene monitoring in plants. It focuses on the three most-used methods – gas chromatography detection, electrochemical sensing and optical detection – and compares them in terms of sensitivity, selectivity, time response and price. Guidelines are provided for proper selection and application of the described sensor methodologies and some specific applications are illustrated of laser-based detector for monitoring ethylene given off by Arabidopsis thaliana upon various nutritional treatments.

Conclusions

Each method has its advantages and limitations. The choice for the suitable ethylene sensor needs careful consideration and is driven by the requirements for a specific application.Key words: Ethylene, Arabidopsis thaliana, gas sampling, gas chromatography, electrochemical sensing, laser-based detector     

Competition for nitrogen between plants and soil microorganisms

Experiments suggest that plants and soil microorganisms are both limited by inorganic nitrogen, even on relatively fertile sites. Consequently, plants and soil microorganisms may compete for nitrogen. While past research has focused on competition for inorganic nitrogen, recent studies have found that plants/mycorrhizae in a wide range of ecosystems can use organic nitrogen. A new view of competitive interactions between plants and soil microorganisms is necessary in ecosystem where plant uptake of organic nitrogen is observed.     

Regulation of ethylene biosynthesis in plants

Ethylene is one of the plant hormones that controls growth and development. There are many responses regulated via ethylene in response to exogenous stimuli. Research on ethylene biosynthesis and the signalling pathway enabled us to understand the mechanism of the regulation of these responses. Different temporal and spatial expression of genes encoding enzymes involved in ethylene biosynthesis is of great importance for the regulation of ethylene responses. Also, post-translational regulation of the enzymes seems to be a key regulatory mechanism for the control of their activity. Because of versatile regulation of its production, ethylene can control plant development at many levels.     

Changes in ethylene production of vernalized plants

The rate of ethylene production (seed/day) in sprouted seedsof radish and pea increased during the first 9 and 13 days,respectively, after the start of low temperature treatment,and decreased thereafter. Ethylene production of vernalizedplants after transfer to high temperature was compared withthat of nonvernalized plants at nearly the same developmentalstage. In all three vernalizable plants, radish, pea and wheat,vernalized seedlings showed decreased rates of ethylene production.After vernalization, a new peak of an unidentified volatile,which was slightly slower than that of ethylene in its retentiontime on gas-chromatography, appeared in all three vernalizableplants. This new peak in radish appeared after about 6 daysof chilling which corresponds to the minimum chilling periodrequired for flower promotion. (Received February 8, 1977; )     

Genetic modulation of ethylene biosynthesis and signaling in plants

With the isolation and characterization of the key enzymes and proteins, and the corresponding genes, involved in ethylene biosynthesis and sensing it has become possible to manipulate plant ethylene levels and thereby alter a wide range of physiological processes. The phytohormone ethylene is an essential signaling molecule that affects a large number of physiological processes; plants deprived of ethylene do not grow and develop normally. In a search for flexible on-off ethylene control, scientists have used inducible organ- and tissue-specific promoters to drive expression of different transgenes. Here, the various strategies that have been used to genetically engineer plants with decreased ethylene biosynthesis and sensitivity are reviewed and discussed.     

Competition for RISC binding predicts in vitro potency of siRNA

Short interfering RNAs (siRNA) guide degradation of target RNA by the RNA-induced silencing complex (RISC). The use of siRNA in animals is limited partially due to the short half-life of siRNAs in tissues. Chemically modified siRNAs are necessary that maintain mRNA degradation activity, but are more stable to nucleases. In this study, we utilized alternating 2′-O-methyl and 2′-deoxy-2′-fluoro (OMe/F) chemically modified siRNA targeting PTEN and Eg5. OMe/F-modified siRNA consistently reduced mRNA and protein levels with equal or greater potency and efficacy than unmodified siRNA. We showed that modified siRNAs use the RISC mechanism and lead to cleavage of target mRNA at the same position as unmodified siRNA. We further demonstrated that siRNAs can compete with each other, where highly potent siRNAs can compete with less potent siRNAs, thus limiting the ability of siRNAs with lower potency to mediate mRNA degradation. In contrast, a siRNA with low potency cannot compete with a highly efficient siRNA. We established a correlation between siRNA potency and ability to compete with other siRNAs. Thus, siRNAs that are more potent inhibitors for mRNA destruction have the potential to out-compete less potent siRNAs indicating that the amount of a cellular component, perhaps RISC, limits siRNA activity.     

Novel inhibitors of ethylene production in higher plants

Of a number of O-substituted hydroxylamine derivatives, N-benzyloxycarbonyl-L-a-aminooxy-propionicacid and -aminooxyacetic acid inhibited ethylene productionby etiolated mung bean hypocotyls by 50% at 3 and 6 µmconcentrations, respectively. Their potency is thus similarto that of aminoethoxyvinylglycine (50% inhibition at 2 µM),the most potent inhibitor of ethylene production hitherto known.Methionine partially alleviated inhibition of ethylene productionby a-aminooxy-acetic acid. The results are in agreement withthe postulated involvement of pyridoxal phosphate in ethylenebiosynthesis. (Received August 31, 1979; )     

Interplay between ethylene and nitrogen nutrition: How ethylene orchestrates nitrogen responses in plants

The stress hormone ethylene plays a key role in plant adaptation to adverse environmental conditions.Nitrogen(N) is the most quantitatively required mineral nutrient for plants,and its availability is a major determinant for crop production.Changes in N availability or N forms can alter ethylene biosynthesis and/or signaling.Ethylene serves as an important cellular signal to mediate root system architecture adaptation,N uptake and translocation,ammonium toxicity,anthocyanin accumulation,and prem...     

Measurement of ethylene binding in plant tissue

Tobacco leaves were exposed to ¹⁴C-labeled ethylene (3.7 × 10⁻² microliters per liter) in the presence and absence of unlabeled ethylene and other compounds. Most of the [¹⁴C]ethylene appears to be bound to displaceable sites. Lineweaver-Burk plots for a one-half maximum response in a tobacco leaf respiration test gave a value of 0.3 microliter per liter for ethylene, 50 microliters per liter for propylene, and 266 microliters per liter for carbon monoxide. Scatchard plots for displacement of [¹⁴C]ethylene from the site gave 0.27 microliters per liter for ethylene, 42 microliters per liter for propylene, and 746 microliters per liter for carbon monoxide. At 2%, CO₂ displaces about 35% of the bound ethylene, but increasing the concentration to 10% does not displace the remaining [¹⁴C]ethylene. A value of 3.5 nanomolar was calculated for the concentration of ethylene-binding sites available to exogenous ethylene. This does not account for the sites occupied by endogenous ethylene, and the total number of binding sites is probably somewhat higher. Using tissue culture material, the system was shown to be stable to freezing and thawing; and the π-acceptors, carbon monoxide, cyanide, n-butyl isocyanide, phosphorous trifluoride, and tetrafluoroethylene, were shown to compete with ethylene for binding.     

A potent inhibitor of ethylene action in plants

Ag(I), applied foliarly as AgNO(3), effectively blocked the ability of exogenously applied ethylene to elicit the classical "triple" response in intact etiolated peas (Pisum sativumcv. Alaska); stimulate leaf, flower, and fruit abscission in cotton (Gossypium hirsutumcv. Stoneville 213); and induce senescence of orchids (Hybrid white Cattleya, Louise Georgeianna). This property of Ag(I) surpasses that of the well known ethylene antagonist, CO(2), and its persistence, specificity, and lack of phytotoxicity at effective concentrations should prove useful in defining further the role of ethylene in plant growth.     

Cross-talk between sulfur assimilation and ethylene signaling in plants

Sulfur (S) deficiency is prevailing all over the world and becoming an important issue for crop improvement through maximising its utilization efficiency by plants for sustainable agriculture. Its interaction with other regulatory molecules in plants is necessary to improve our understanding on its role under changing environment. Our knowledge on the influence of S on ethylene signaling is meagre although it is a constituent of cysteine (Cys) required for the synthesis of reduced glutathione (GSH) and S-adenosyl methionine (SAM), a precursor of ethylene biosynthesis. Thus, there may be an interaction between S assimilation, ethylene signaling and plant responses under optimal and stressful environmental conditions. The present review emphasizes that responses of plants to S involve ethylene action. This evaluation will provide an insight into the details of interactive role of S and ethylene signaling in regulating plant processes and prove profitable for developing sustainability under changing environmental conditions.     

A role for ethylene in the metabolism of cyanide by higher plants

The action of ethylene on the capacity of plant tissues to metabolize cyanide to β-cyanoalanine was examined. Beta-cyanoalanine synthase (EC 4.4.1.9) catalyzes the reaction between cyanide and cysteine to form β-cyanoalanine and hydrogen sulfide. Levels of β-cyanoalanine synthase activity in tissues of 6 day old etiolated pea (Pisum sativum) seedlings were enhanced severalfold by 1 microliter per liter ethylene. The promotive effect of ethylene increased with increasing ethylene concentrations from 0.01 to 100 microliters per liter and with the period of exposure from 3 to 24 hours. Ethylene enhanced β-cyanoalanine synthase activity in all regions of the seedling (shoots and roots, internodal regions, cotyledons). The promotive effect was eliminated by norbornadiene, a competitive inhibitor of ethylene action. Levels of β-cyanoalanine synthase in seedlings of four other dicots (Phaseolus aureas, Glycine max, Lactuca sativa, Sinapis arvensis) and two monocots (Hordeum vulgares, Triticum aestivum) were also increased in response to ethylene. Our results suggest an important regulatory role for ethylene in the metabolism of cyanide by higher plants.     

Effect of antagonists of ethylene action on binding of ethylene in cut carnations

Five hours after cut carnations had been treated with a pulse of 1 or 4 mM silver thiosulfate (STS), in vivo ethylene binding in petals was inhibited by 22 and 29%, respectively. When binding was measured 4 days after the 4-mM STS treatment, binding was inhibited by 81%. 2,5-Norbornadiene, which substantially delays carnation senescence, inhibited ethylene binding by 41% at a concentration of 1000 l/l. The Kd for ethylene binding in carnations was estimated to be 0.1 l/l in petals and 0.09 l/l in leaves. The concentration of binding sites was estimated to be 6.0×10^–9 mol/kg of petals and 2.0×10^–9 mol/kg of leaves     

A MAPK pathway mediates ethylene signaling in plants

Ethylene signal transduction involves ETR1, a two-component histidine protein kinase receptor. ETR1 functions upstream of the negative regulator CTR1. The similarity of CTR1 to members of the Raf family of mitogen-activated protein kinase kinase kinases (MAPKKKs) suggested that ethylene signaling in plants involves a MAPK pathway, but no direct evidence for this has been provided. Here we show that distinct MAPKs are activated by the ethylene precursor aminocyclopropane-1-carboxylic acid (ACC) in Medicago and ARABIDOPSIS: In Medicago, the ACC-activated MAPKs were SIMK and MMK3, while in Arabidopsis MPK6 and another MAPK were identified. Medicago SIMKK specifically mediated ACC-induced activation of SIMK and MMK3. Transgenic Arabidopsis plants overexpressing SIMKK have constitutive MPK6 activation and ethylene-induced target gene expression. SIMKK overexpressor lines resemble ctr1 mutants in showing a triple response phenotype in the absence of ACC. Whereas MPK6 was not activated by ACC in etr1 mutants, ein2 and ein3 mutants showed normal activation profiles. In contrast, ctr1 mutants showed constitutive activation of MPK6. These data indicate that a MAPK cascade is part of the ethylene signal transduction pathway in plants.     

The measurement of ethylene binding and metabolism in plant tissue

Methods are described for the rigorous measurement of C₂H₄ metabolism and C₂H₄ binding in plant tissue. Comparisons are drawn between the results obtained using other methods and those which emerge from our studies, indicating that significant misapprehensions may have arisen in relation both to the distribution of metabolism and binding.