Growth inhibition of pollen tubes by blocking the aromatic or branched-chain amino acid pathways of biosynthesis

A number of organic molecules that appear to block the ethylene receptor have been discovered recently. For example, on irradiation with visible light, diazocyclopentadiene (DACP), gives rise to some potent but as yet unidentified inhibitor compounds. Some synthetic cyclopropenes have been shown to bind to the ethylene receptor and prevent the physiological action of ethylene for extended periods. Cyclopropene (CP). 1-methylcyclopropene (1-MCP) and 3,3-dimethylcyclopropene (3,3-DMCP) have been shown to prevent ethylene effects in a number of plants. As low a concentration as 0.5 nl l⁻¹ of 1-MCP is sufficient to protect carnation ( Dianthus caryophyllus ) flowers for several days against ethylene, and 0.7 nl l⁻¹ 1-MCP or CP will prevent the ripening of banana ( Musa sapientum ) for 12 days at 24°C. Some plant organs require higher concentrations of these inhibitors. Complete inhibition of ethylene effects in pea seedlings requires treatment with 40 n1 1⁻¹ of 1-MCP. These novel inhibitors appear to be suitable for many commercial applications including extending the vase life of cut flowers and the display life of potted plants. Since 1-MCP apparently is non-toxic at concentrations that are active, it may in future be available for regulating the ripening of fruits and preventing the deleterious effects of ethylene in vegetables.     

The discovery and development of compounds counteracting ethylene at the receptor level

The discovery and development of 1-methylcyclopropene (1-MCP) was not done as a single step but rather was found by studying various aspects of ethylene action and the ethylene receptors. It was first noted that 2, 5-norbornadiene seemed to counteract ethylene. Studies showed it was a competitive inhibitor of ethylene responses, and knowledge that ethylene antagonists like ethylene agonists bound to silver in the same order as they were active as inhibitors was obtained. Ring strain appeared to be a primary factor that led to trans-cyclooctene then to diazocyclopentadiene. This same concept allowed for the use of chemical concepts that lead to cyclopropenes. More recent work indicates additional factors can come into play in the development of ethylene antagonists at the receptor level and these are now being utilized to find additional and improved antagonists. 1-MCP is likely to remain a primary means of controlling ethylene responses for the immediate future.     

Deciphering the Role of Ethylene in Plant–Herbivore Interactions

Most plants emit ethylene in response to herbivory by insects from many different feeding guilds. The elicitors of these ethylene emissions are thought to be microorganisms or oral secretion-specific compounds that are transferred when the attacking insect feeds. To find the receptors for these elicitors and describe the signaling cascades that are subsequently activated will be the challenge of future research. Past experiments on the function of herbivore-induced ethylene, which were biased toward the use of chemical treatments to manipulate ethylene, identified seven ethylene-dependent defense responses. In contrast, a genetic toolbox that consists of several mutants has rarely been used and to date, mutants have helped to identify only one additional ethylene-dependent defense response. Ethylene-dependent responses include the emission of specific volatile organic compounds as indirect defense, the accumulation of phenolic compounds, and proteinase inhibitor activity. Besides being ethylene regulated, these defenses depend strongly on the wound-hormone jasmonic acid (JA). That ethylene requires the concomitant induction of JA, or other signals, appears to be decisive. Rather than being the principal elicitor of defense responses, ethylene modulates the sensitivity to a second signal and its downstream responses. Given this modulator role, and the artifacts associated with the use of chemical treatments to manipulate ethylene production and perception, future advances in the study of ethylene’s function in plant–herbivore interactions will likely come from the use of signaling mutants or transgenic plants. It will be exciting to see if adaptive phenotypic plasticity is largely an ethylene-mediated response.     

采后果蔬对乙烯受体抑制剂的响应及贮运保鲜技术的研究

近几年来 ,随着重氮环戊二烯和环丙烯类等乙烯受体抑制剂的发现 ,为控制乙烯敏感型的果蔬采后成熟、衰老提供新的技术手段。从乙烯受体抑制剂的特性、作用特点以及可能作用机理等方面概述了采后果蔬对乙烯受体抑制剂的响应和应用乙烯受体抑制剂延长采后果蔬贮运保鲜的技术。     

Role of ethylene receptors during senescence and ripening in horticultural crops

The past two decades have been rewarding in terms of deciphering the ethylene signal transduction and functional validation of the ethylene receptor and downstream genes involved in the cascade. Our knowledge of ethylene receptors and its signal transduction pathway provides us a robust platform where we can think of manipulating and regulating ethylene sensitivity by the use of genetic engineering and making transgenic. This review focuses on ethylene perception, receptor mediated regulation of ethylene biosynthesis, role of ethylene receptors in flower senescence, fruit ripening and other effects induced by ethylene. The expression behavior of the receptor and downstream molecules in climacteric and non climacteric crops is also elaborated upon. Possible strategies and recent advances in altering the ethylene sensitivity of plants using ethylene receptor genes in an attempt to modulate the regulation and sensitivity to ethylene have also been discussed. Not only will these transgenic plants be a boon to post-harvest physiology and crop improvement but, it will also help us in discovering the mechanism of regulation of ethylene sensitivity.     

Ethylene regulation of fruit ripening: Molecular aspects

Progress in ethylene regulating fruit ripening concerning itsperception and signal transduction and expression of ACC synthaseand ACC oxidase genes is reviewed. ACC synthase and ACC oxidasehave been characterized and their genes cloned from various fruittissues. Both ACC synthase and ACC oxidase are encoded bymultigene families, and their activities are associated withfruit ripening. In climacteric fruit, the transition toautocatalytic ethylene production appears to be due to a seriesof events in which ACC sythase and ACC oxidase genes have beenexpressed developmentally. Differential expression of ACCsynthase and ACC oxidase gene family members is probably involvedin such a transition that ultimately controls the onset of fruitripening.In comparison to ACC synthase and ACC oxidase, less is knownabout ethylene perception and signal transduction because of thedifficulties in isolating and purifying ethylene receptors orethylene-binding proteins using biochemical methods. However, theidentification of the Nr tomato ripening mutant as anethylene receptor, the applications of new potent anti-ethylenecompounds and the generation of transgenic fruits with reducedethylene production have provided evidence that ethylenereceptors regulate a defined set of genes which are expressedduring fruit ripening. The properties and functions of ethylenereceptors, such as ETR1, are being elucidated.Application of molecular genetics, in combination withbiochemical approaches, will enable us to better understand theindividual steps leading from ethylene perception and signaltransduction and expression of ACC synthase and ACC oxidase genefamily member to the physiological responses.     

Control of ethylene activity in various plant systems by structural analogues of 1-methylcyclopropene

Two structural analogues of 1-methylcyclopropene (1-MCP), 1-ethylcyclopropene (1-ECP) and 1-propylcyclopropene (1-PCP) were found to inhibit ethylene action and thereby the responses to ethylene in various plant systems. When applied prior to exposure to ethylene, the analogues considerably delayed ethylene-induced ripening of avocado and tomato fruits, delayed citrus leaf explants abscission and reversed ethylene-induced swelling and inhibition of elongation in etiolated pea plants. The analogues exerted their effect in a concentration-depended manner, at a range of several parts per million. Of the two analogues, 1-ECP was found in all cases more potent than 1-PCP but less potent then the mother compound 1-MCP. It is proposed that the analogues inhibit ethylene action by competing for the sites of binding on the ethylene receptor, similar to the mode of action suggested for 1-MCP. Findings revealed in this study imply that the competition of ethylene and the analogues for the ethylene site of binding is of a non-competitive nature. The analogues effectively inhibited ethylene action only if applied before the plant material was exposed to ethylene, or in the case of fruits shortly after harvest. Simultaneous application of the analogues and ethylene reduced the inhibitory effect of the analogues. Application of the analogues after exposure to ethylene or after fruit ripening had nullified the inhibitory effect of the analogues. Ripening of fruits, treated with the analogues, was inhibited for a finite period of time after which the fruits ripened normally. This resumption of ripening ability is attributed to presence of free binding sites on the ethylene receptor at the point of recovery from the inhibition. As the analogues are volatile, non-corrosive, non-toxic, odorless compounds and effective at minute concentrations, they can be considered promising candidates for practical use.     

1-甲基环丙烯采后处理对樱桃番茄果实成熟过程的影响

研究了不同浓度(0、0.035、0.07和0.11μL/L)的乙烯受体竞争性抑制剂1-甲基环丙烯(1-MCP)采后处理对绿熟期樱桃番茄的乙烯合成、果实软化、果实色素(叶绿素、茄红素、β-胡萝卜素)含量消长的影响.0.07 μL/L及其以上浓度的1-MCP降低了前期乙烯合成,同时推迟了乙烯释放高峰,但0.035 μL/L浓度的1-MCP处理并不能抑制内源乙烯合成.1-MCP显著延迟了果实软化和叶绿素降解,但并不影响这两个过程的启动.茄红素合成的启动和积累均受到了1-MCP抑制,而1-MCP并不推迟β-胡萝卜素合成的启动,只抑制其积累.这些结果提示了乙烯调节成熟生理过程的不同机制.对于绿熟期的樱桃番茄,0.07～0.11μL/L的1-MCP是实用的有效处理浓度.1-MCP有效浓度可能用于了解果实的乙烯受体水平和乙烯敏感性.     

Ethylene and fruit ripening

The latest advances in our understanding of the relationship between ethylene and fruit ripening are reviewed. Considerable progress has been made in the characterisation of genes encoding the key ethylene biosynthetic enzymes, ACC synthase (ACS) and ACC oxidase (ACO) and in the isolation of genes involved in the ethylene signal transduction pathway, particularly those encoding ethylene receptors ( ETR ). These have allowed the generation of transgenic fruit with reduced ethylene production and the identification of the Nr tomato ripening mutant as an ethylene receptor mutant. Through these tools, a clearer picture of the role of ethylene in fruit ripening is now emerging. In climacteric fruit, the transition to autocatalytic ethylene production appears to result from a series of events where developmentally regulated ACO and ACS gene expression initiates a rise in ethylene production, setting in motion the activation of autocatalytic ethylene production. Differential expression of ACS and ACO gene family members is probably involved in such a transition. Finally, we discuss evidence suggesting that the NR ethylene perception and transduction pathway is specific to a defined set of genes expressed in ripening climacteric fruit and that a distinct ETR pathway regulates other ethylene-regulated genes in both immature and ripening climacteric fruit as well as in non-climacteric fruit. The emerging picture is one where both ethylene-dependent and -independent pathways coexist in both climacteric and non-climacteric fruits. Further work is needed in order to dissect the molecular events involved in individual ripening processes and to understand the regulation of the expression of both ethylene-dependent and -independent genes.     

Effects of novel oxime ether derivatives of aminooxyacetic acid on ethylene formation in leaves of oilseed rape and barley and on carnation flower senescence

New derivatives of aminooxyacetic acid were tested for their ability to inhibit ethylene formation in higher plants. Treatments with {[(isopropylidene)-aminojoxy}-acetic acid-2-(methoxy)-2-oxoethyl ester, {[(isopropylidene)-aminojoxy}-acetic acid-2-(hexyloxy)-2-oxoethyl ester or {[(cyclohexylidene)-amino]oxy}-acetic acid-2-(isopropyloxy)-2-oxoethyl ester reduced ethylene evolution by leaf discs of oilseed rape and drought-stressed barley leaves. The new compounds delayed senescence of cut carnation flowers. The endogenous levels of 1-aminocyclopropane-1-carboxylic acid (ACC) and its N-malonyl conjugate were also reduced in the leaf discs of oilseed rape. This suggests that a step in the biosynthesis of ethylene, prior to the formation of ACC, is inhibited by these new compounds. A lag phase in response suggests that these compounds have to be activated most likely by the production of metabolites with a free aminooxy group.     

Ethylene and plant responses to stress

When plants are subject to a variety of stresses they often exhibit symptoms of exposure to ethylene. Although this relationship usually results from induction of ACC synthase thus raising the concentration of the precursor of ethylene, it is now apparent that there are numerous other ways that stresses produce ethylene-like symptoms. This complex relationship between stress and ethylene-like symptoms is here termed the stress ethylene syndrome. ACC synthase exists as a multi-gene family whose individual members are differentially regulated, many by various stresses. In addition, ACC oxidase. AdoMet synthetase, enzymes in the Yang methionine cycle, and enzymes that conjugate ACC are regulated by stress. In more unusual cases, ethylene production is not increased by stress or may be reduced. There is evidence for stress effects on perception of ethylene and the potential exists that some steps of the ethylene signal transduction pathway may be influenced by stress. Because of the variability possible in the stress ethylene syndrome, it continues to be studied for a number of stresses and species. In particular, attention is being given to wounding, mechanical stress, drought, heat and water deficit stress, chilling, air pollution, chemical and salt stress, and low O₂stress. It is becoming more apparent that a number of stress responses involve interactions with other hormones.     

乙烯受体差异性协作与Raf-like蛋白CTR1负调控的乙烯信号转导

以拟南芥为模式植物研究植物激素乙烯信号转导,在过去20年来取得了长足进展,并以遗传学与生物化学为基础建立了一个线性的信号转导途径模型．虽然这个模型基本上解释了乙烯信号组分参与的信号传递过程,但是,其中仍然存在若干问题亟待进一步研究．例如,上游的多个乙烯受体家族成员与CONSTITUTIVETRIPLE—RESPONSE1蛋白如何协同作用,下游的ETHYLENEINsENsITIVE2（EIN2）如何将乙烯信号传递给转录激活因子EIN3,以及是否存在其他的信号途径调控乙烯反应等．本文将着重阐述不同乙烯受体家族成员的协作对乙烯信号途径的差异性调控,植物利用多个乙烯受体感受乙烯的生物学意义,以及乙烯受体除了通过CTR1蛋白调节EIN2功能外,是否还存在其他的信号转导途径．     

花衰老相关的乙烯信号转导基因研究进展

乙烯在许多切花衰老过程中起着重要的调节作用,不同的植物乙烯信号转导组分在花衰老过程中有不同的转录调节特性。根据乙烯信号转导标准模式,通过调节乙烯信号转导基因表达能够调控花对乙烯的敏感性,深入研究乙烯信号转导机制;可能有多条途径可延缓切花衰老。综述了香石竹和月季等几种观赏植物在花衰老过程中乙烯受体和乙烯信号转导基因表达及特性。     

Identification of Novel Inhibitors of 1-Aminocyclopropane-1-carboxylic Acid Synthase by Chemical Screening in Arabidopsis thaliana

Ethylene is a gaseous hormone important for adaptation and survival in plants. To further understand the signaling and regulatory network of ethylene, we used a phenotype-based screening strategy to identify chemical compounds interfering with the ethylene response in Arabidopsis thaliana. By screening a collection of 10,000 structurally diverse small molecules, we identified compounds suppressing the constitutive triple response phenotype in the ethylene overproducer mutant eto1-4. The compounds reduced the expression of a reporter gene responsive to ethylene and the otherwise elevated level of ethylene in eto1-4. Structure and function analysis revealed that the compounds contained a quinazolinone backbone. Further studies with genetic mutants and transgenic plants involved in the ethylene pathway showed that the compounds inhibited ethylene biosynthesis at the step of converting S-adenosylmethionine to 1-aminocyclopropane-1-carboxylic acid (ACC) by ACC synthase. Biochemical studies with in vitro activity assay and enzyme kinetics analysis indicated that a representative compound was an uncompetitive inhibitor of ACC synthase. Finally, global gene expression profiling uncovered a significant number of genes that were co-regulated by the compounds and aminoethoxyvinylglycine, a potent inhibitor of ACC synthase. The use of chemical screening is feasible in identifying small molecules modulating the ethylene response in Arabidopsis seedlings. The discovery of such chemical compounds will be useful in ethylene research and can offer potentially useful agrochemicals for quality improvement in post-harvest agriculture.     

利用海洋硅藻生产生物活性物质研究进展*

生物活性物质在食品、饵料、化妆品、保健品和医药等行业具有广阔的应用前景,其研究早已受到广泛关注。鉴于海洋硅藻具有生长速度快、生物活性物质含量高、易于规模培养、便于提取等诸多优势,为理想的生物活性物质生产者。尽管国内外已进行了大量利用海洋硅藻生产生物活性物质的研究,但是受限于培养工艺老旧、生产成本过高等缺陷,商业化利用海洋硅藻开发生物活性物质依然停滞不前。阐述海洋硅藻五种常见生物活性物质的应用价值,进一步探讨海洋硅藻高产生物活性物质的策略,就如何低成本、高效开发利用硅藻源生物活性物质提出建议,为海洋硅藻商业化开发利用提供参考。     

1-substituted cyclopropenes: Effective Blocking Agents for Ethylene Action in Plants

A series of 1-alkane substituted cyclopropenes has been prepared and tested as ethylene antagonists using banana fruits as an assay system. 1-Methyl-, 1-ethyl-, 1-propyl-, 1-butyl-, 1-pentyl-, 1-hexyl-, 1-heptyl-, 1-octyl-, 1-nonyl-, and 1-decylcyclopropene were all very active compounds. 1-Methylcyclopropene protected bananas from ethylene with a minimum concentration of 0.7 nl.l^–1 after a 24 h exposure. As the carbon chain length was extended the minimum requirement increased some, but starting with 1-butylcyclopropene, the minimum concentration requirement declined and many cyclopropenes were required in lower concentrations than 1-methylcyclopropene. The time of protection at ambient temperature (22–23 °C) was 12 d for 1-methyl-, 1-ethyl-, 1-propyl-, and 1-butylcyclopropene. 1-Pentylcyclopropene protected bananas for 14 d, 1-hexylcyclopropene for 20 d, 1-heptylcyclopropene for 21 d, 1-octylcyclopropene for 25 d, 1-nonylcyclopropene for 35 d, and 1-decylcyclopropene for 36 d.     

Flower Abscission in Excised Inflorescences of Three Plectranthus Cultivars

Flower abscission induced by ethylene in three Plectranthus cultivars was investigated in order to characterise response to a range of inhibitory and antagonistic compounds. Excised inflorescences were exposed to 100 ml l⁻¹ ethylene gas or placed in various concentrations of ethephon (277, 27.7, 2.77, 0.277 and 0.0277 μM). Flower abscission in Plectranthus was readily induced by applying ethylene gas and by the 277 μM dose of ethephon. Removal of the inflorescences from the ethylene treatment prevented subsequent flower abscission. This implies that ethylene treatment did not induce an autocatalytic production of ethylene. Compounds that are known to compete for the ethylene receptor (100 and 500 ppb 1-methylcyclopropene or 100 and 500 ppm 2,5-norbornadiene) did not reduce abscission in this system. Also, application of the ethylene biosynthesis inhibitor, aminooxyacetic acid at 1 mM, was ineffective at preventing ethylene-induced flower abscission. In contrast, one compound known to block protein production (100 μM cycloheximide) and a non-competitive inhibitor of ethylene action (2 mM silver thiosulfate) did prevent ethylene-induced abscission. We conclude that flower abscission in cut inflorescences of Plectranthus is very likely mediated by endogenous ethylene production, but that control of ethylene-induced flower abscission in this genus can not be readily obtained by most ethylene antagonists that are known to be effective in other systems.     

The role of ethylene and wound signaling in resistance of tomato to Botrytis cinerea

Ethylene, jasmonate, and salicylate play important roles in plant defense responses to pathogens. To investigate the contributions of these compounds in resistance of tomato (Lycopersicon esculentum) to the fungal pathogen Botrytis cinerea, three types of experiments were conducted: (a) quantitative disease assays with plants pretreated with ethylene, inhibitors of ethylene perception, or salicylate; (b) quantitative disease assays with mutants or transgenes affected in the production of or the response to either ethylene or jasmonate; and (c) expression analysis of defense-related genes before and after inoculation of plants with B. cinerea. Plants pretreated with ethylene showed a decreased susceptibility toward B. cinerea, whereas pretreatment with 1-methylcyclopropene, an inhibitor of ethylene perception, resulted in increased susceptibility. Ethylene pretreatment induced expression of several pathogenesis-related protein genes before B. cinerea infection. Proteinase inhibitor I expression was repressed by ethylene and induced by 1-methylcyclopropene. Ethylene also induced resistance in the mutant Never ripe. RNA analysis showed that Never ripe retained some ethylene sensitivity. The mutant Epinastic, constitutively activated in a subset of ethylene responses, and a transgenic line producing negligible ethylene were also tested. The results confirmed that ethylene responses are important for resistance of tomato to B. cinerea. The mutant Defenseless, impaired in jasmonate biosynthesis, showed increased susceptibility to B. cinerea. A transgenic line with reduced prosystemin expression showed similar susceptibility as Defenseless, whereas a prosystemin-overexpressing transgene was highly resistant. Ethylene and wound signaling acted independently on resistance. Salicylate and ethylene acted synergistically on defense gene expression, but antagonistically on resistance.     

Influence of ethylene and Ag+ on hypocotyl growth in etiolated lupin seedlings. Effects on cell growth and division

Lupin seeds treated with 1-amino-cyclopropane-1-carboxylic acid (ACC) or2-chloroethylphosphonic acid (CEPA) produced hypocotyls showing a typicalethylene growth response (reduced elongation and increased thickness), whichcould be efficiently counteracted by the presence of silver thiosulfate (STS).The fact that ACC and CEPA stimulated the ethylene produced in different zonesalong the hypocotyls suggests that these compounds, which are stored in theseeds during treatment, were transported to and along the hypocotyl. The same istrue in hypocotyls from STS-treated seeds, which indicates that stress ethyleneis induced by metal toxicity. CEPA was more effective than ACC in both producingethylene and influencing growth due to the high capacity of the hypocotyl toconjugate ACC. At the same time that CEPA inhibited hypocotyl elongation, thehypocotyl diameter increased and ethylene production exceeded the maximum valueof the control. The subsequent recovery of hypocotyl elongation coincided with adecrease in ethylene production and involved cell elongation. The final celllength was similar (in ACC-) or higher (in CEPA-treated plants) than in thecontrol, although the hypocotyls were shorter in both cases, while the number ofcells per column was reduced to half that observed in the control. Thisinhibition of cell division caused by ethylene was selective since the number ofcell layers did not change. The variations in cell diameter in the epidermisand, especially, in the cortex and pith were correlated with the variations inhypocotyl diameter produced by ACC, CEPA and STS. The results show that theethylene-induced hypocotyl thickening was irreversible and mainly due to anincrease in cell diameter, while the inhibition of hypocotyl elongation wasreversible and involved irreversible inhibition of cell division and,paradoxically, stimulation of cell elongation to produce cells longer than thoseof the control.     

Phage display: an important tool in the discovery of peptides with anti-HIV activity

Human immunodeficiency virus (HIV) remains a worldwide health problem despite huge investments and research breakthroughs, and no single drug is effective in killing the virus yet. Among new strategies to control HIV infection, the phage display (PD) technology has become a promising tool in the discovery of peptides that can be used as new drugs, or also as possible vaccine candidates. This review discusses basic aspects of PD and its use to advance two main objectives related to combating HIV-1 infection: the identification of peptides that inhibit virus replication and the identification of peptides that induce the production of neutralizing antibodies. We will cover the different approaches used for mapping and selection of mimotopes, and discuss the promising results of these biologicals as antiviral agents.