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.     

Induction of a Citrus gene highly homologous to plant and yeast thi genes involved in thiamine biosynthesis during natural and ethylene-induced fruit maturation

Maturing citrus fruit undergo pigment changes which can be enhanced by exogenous ethylene. In order to identify genes induced by ethylene in citrus fruit peel, we cloned the gene c-thi1. mRNA corresponding to c-thi1 increased gradually in the peel during natural fruit maturation and in response to ethylene. GA₃ pretreatment reduced the inductive effect of ethylene. Levels of c-thi1 increased also in juice sacs but the effect of ethylene was much less prominent. c-thi1 is homologous to yeast and plant genes encoding for an enzyme belonging to the pathway of thiamine biosynthesis. The data suggest that thiamine is involved in citrus fruit maturation.     

The effect of chemical structure on the antagonism by cyclopropenes of ethylene responses in banana

The compounds, cyclopropene, 1-methylcyclopropene, 3-methylcyclopropene, 1,3-dimethylcyclopropene, 3,3-dimethylcyclopropene, 1,3,3-trimethylcyclopropene, 3-methyl-3-vinylcyclopropene, and 3-methyl-3-ethynylcyclopropene, and 1,2-dimethylcyclopropene were tested as antagonists to the ethylene receptor in bananas. All of the compounds inactivated the receptor and the bananas did not respond to ethylene even at 1000 nL L^–1. Large differences were found in the concentration required (0.7–20,000 nL L^–1 for 24h) to inactivate the receptor and in the duration of inactivation (3–12 days at 24C depending on the compound). After this time the bananas responded to ethylene and appeared to ripen normally.     

Ethylene perception is involved in female cucumber flower development

It is well established that ethylene promotes female flower development in cucumber. However, little is known about how the gaseous hormone selectively affects female flowers, and what mechanism it uses. Previously, we found organ‐specific DNA damage in the primordial anther of female cucumber flowers. This finding led to a hypothesis that ethylene might promote female flower development via the organ‐specific induction of DNA damage in primordial anthers. In this study, we tested this hypothesis first by demonstrating ethylene induction of DNA damage via the ethylene signaling pathway using cucumber protoplasts. Then, using representative component genes of the ethylene signaling pathway as probes, we found that one of the ethylene receptors, CsETR1, was temporally and spatially downregulated in the stamens of stage‐6 female cucumber flowers, especially along with the increase of the nodes. Furthermore, by constructing transgenic Arabidopsis plants with organ‐specific expression of antisense CsETR1 under the control of an AP3 promoter to downregulate ETR1 expression in the stamens, we generated Arabidopsis ‘female flowers’, in which the abnormal stamens mimic those of female cucumber flowers. Our data suggest that ethylene perception is involved in the arrest of stamen development in female cucumber flowers through the induction of DNA damage. This opens up a novel perspective and approach to solve the half‐century‐long puzzle of how gaseous ethylene selectively promotes female flowers in the monoecious cucumber plant.     

New volatile and water-soluble ethylene antagonists

Twenty cyclopropenes were prepared and their anti-ethylene activity was evaluated in the fruit ripening and plant senescence bioassays. The treatment of banana fruits with developed antagonists led to delay of fruit ripening. Some antagonists were capable to extend exhibition life of cut mini carnation flowers as well as delay senescence of bean leaves. The potency of ethylene antagonists declined with increase in molecular weight and reduction in their solubility in water, irrespective of bioassay used. Published in Russian in Fiziologiya Rastenii, 2006, Vol. 53, No. 4, pp. 585–591. The text was submitted by the author in English.     

The never ripe mutation blocks ethylene perception in tomato.

Seedlings of tomato fruit ripening mutants were screened for their ability to respond to ethylene. Ethylene induced the triple response in etiolated hypocotyls of all tomato ripening mutants tested except for one, Never ripe (Nr). Our results indicated that the lack of ripening in this mutant is caused by ethylene insensitivity. Segregation analysis indicated that Nr-associated ethylene insensitivity is a single codominant trait and is pleiotropic, blocking senescence and abscission of flowers and the epinastic response of petioles. In normal tomato flowers, petal abscission and senescence occur 4 to 5 days after the flower opens and precede fruit expansion. If fertilization does not occur, pedicel abscission occurs 5 to 8 days after petal senescence. If unfertilized, Nr flowers remained attached to the plant indefinitely, and petals remained viable and turgid more than four times longer than their normal counterparts. Fruit development in Nr plants was not preceded by petal senescence; petals and anthers remained attached until they were physically displaced by the expanding ovary. Analysis of engineered 1-aminocyclopropane-1-carboxylate (ACC) synthase-overexpressing plants indicated that they are phenotypic opposites of Nr plants. Constitutive expression of ACC synthase in tomato plants resulted in high rates of ethylene production by many tissues of the plant and induced petiole epinasty and premature senescence and abscission of flowers, usually before anthesis. There were no obvious effects on senescence in leaves of ACC synthase overexpressers, suggesting that although ethylene may be important, it is not sufficient to cause tomato leaf senescence; other signals are clearly involved.     

Ethylene receptor expression is regulated during fruit ripening, flower senescence and abscission

Using theArabidopsis ethylene receptorETR1 as a probe, we have isolated a tomato homologue (tETR) from a ripening cDNA library. The predicted amino acid sequence is 70% identical toETR1 and homologous to a variety of bacterial two component response regulators over the histidine kinase domain. Sequencing of four separate cDNAs indicates that tETR lacks the carboxyl terminal response domain and is identical to that encoded by the tomatoNever ripe gene. Ribonuclease protection showed tETR mRNA was undetectable in unripe fruit or pre-senescent flowers, increased in abundance during the early stages of ripening, flower senescence, and in abscission zones, and was greatly reduced in fruit of ripening mutants deficient in ethylene synthesis or response. These results suggest that changes in ethylene sensitivity are mediated by modulation of receptor levels during development.     

乙烯受体在果实成熟及花衰老中的研究进展

乙烯受体是乙烯信号转导网络的第一个转导元件,通过调控受体基因的表达,可以调节植物对乙烯的敏感性,以调控果实的成熟及花衰老进程的响应.随着人们对乙烯受体研究的深入,乙烯受体突变体及受体抑制剂在采后果实和切花保鲜上的应用已受到广泛关注.就近年来关于乙烯受体的相关研究进展进行综述,重点介绍了乙烯受体的分子调控机制及乙烯受体在...     

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     

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。     

番茄果实中乙烯与多聚半乳糖醛酸酶的关系

乙烯与多聚半乳糖醛酸酶(PG)都是果实成熟过程中关键的调节因子.一方面,在有乙烯合成缺陷的转反义ACS番茄和乙烯感受缺陷的Nr突变体番茄果实中PG基因表达量都明显下降,PG酶活性明显降低;用外源乙烯(100 μL/L)处理绿熟期番茄果实使PG基因的表达明显增强,而1-甲基环丙烯(1-MCP,1 μL/L)处理转色期番茄果实明显抑制PG基因表达.另一方面,转反义PG基因番茄果实乙烯释放量在授粉后低于其野生型,番茄乙烯受体基因LeETR4和乙烯反应因子LeERF2基因表达量比野生种低.PG降解果胶的产物D-GA(100 mg/L)促进未熟期番茄果实中的乙烯生成和LeETR4、LeERF2基因的表达.     

Precise spatio‐temporal modulation of ACC synthase by MPK6 cascade mediates the response of rose flowers to rehydration

Drought is a major abiotic stress that affects the development and growth of most plants, and limits crop yield worldwide. Although the response of plants to drought has been well documented, much less is known about how plants respond to the water recovery process, namely rehydration. Here, we describe the spatio‐temporal response of plant reproductive organs to rehydration using rose flowers as an experimental system. We found that rehydration triggered rapid and transient ethylene production in the gynoecia. This ethylene burst serves as a signal to ensure water recovery in flowers, and promotes flower opening by influencing the expression of a set of rehydration‐responsive genes. An in‐gel kinase assay suggested that the rehydration‐induced ethylene burst resulted from transient accumulation of RhACS1/2 proteins in gynoecia. Meanwhile, RhMPK6, a rose homolog of Arabidopsis thaliana MPK6, is rapidly activated by rehydration within 0.5 h. Furthermore, RhMPK6 was able to phosphorylate RhACS1 but not RhACS2 in vitro. Application of the kinase inhibitor K252a suppressed RhACS1 accumulation and rehydration‐induced ethylene production in gynoecia, and the protein phosphatase inhibitor okadaic acid had the opposite effect, confirming that accumulation of RhACS1 was phosphorylation‐dependent. Finally, silencing of RhMPK6 significantly reduced ethylene production in gynoecia when flowers were subjected to rehydration. Taken together, our results suggest that temporal‐ and spatial‐specific activation of an RhMPK6‐RhACS1 cascade is responsible for rehydration‐induced ethylene production in gynoecia, and that the resulting ethylene‐mediated signaling pathway is a key factor in flower rehydration.     

Ethylene and vegetative development

The past decade has witnessed a tremendous increase in our understanding of the role of ethylene in plant development. Genes encoding enzymes of the ethylene biosynthesis pathway have been isolated, allowing the manipulation of endogenous ethylene levels in intact plants. In parallel, a collection of ethylene mutants was obtained by using a simple response assay. This resulted in the identification of several genes involved in ethylene signal transduction. The data obtained using these new tools have allowed long-standing hypotheses to be tested, while gaining novel insight into the function of ethylene in development. Recent molecular evidence supported the existence of an intense hormonal cross-talk during plant growth. Numerous processes are controlled by ethylene in a close interaction with auxin, and often it was impossible to differentiate between auxin and ethylene effects. Molecular-genetic tools are now allowing the dissection of these interactions. Ethylene does not seem essential for many developmental processes. Nevertheless, it is of crucial importance for survival in most species as it occupies a key position in the developmental response mechanisms of plants under mechanical stress.     

In vitro growth and ripening of strawberry fruit in the presence of ACC, STS or propylene

Strawberry ( Fragaria ananassa Duch.) fruit exhibit limited capacity for continued development following harvest. This problem can be circumvented by maintaining harvested strawberry fruit in solutions containing sucrose and a bactericide. In this study, we investigated the respiratory and ethylene production kinetics and ethylene responsiveness in strawberry fruit harvested immature and ripened in vitro in the presence of propylene. The effects of 1-amino-cyclopropane-1-carboxylic acid (ACC) and silver thiosulfate (STS) alone and in combination were also examined. Respiration and ethylene patterns of fruit harvested green and developed in vitro declined with maturation and ripening, as did those of field-grown fruit harvested at different stages of ripeness. Exposure of detached green strawberry fruit to 5000 μl litre^-1 propylene failed to stimulate respiration or ethylene production, but advanced pigmentation changes and fresh-weight gain significantly. Excised fruit provided with 1 mol^-3 ACC exhibited increased ethylene production, enhanced fresh-weight gain, and accelerated anthocyanin accumulation, but showed no change in respiration. The developmental response of harvested strawberry fruit to propylene or ACC was dependent on fruit maturity at harvest, with white fruit exhibiting greater insensitivity compared with green fruit. Silver thiosulfate (0.5 mol^-3) applied alone or in combination with ACC failed to delay ripening in excised strawberry fruit. These experiments demonstrate that ripening in detached strawberry fruit can be modified by ethylene only in green fruit that are provided with a carbohydrate source. Ethylene, when applied exogenously as ACC or propylene to green fruit, can slightly increase fruit growth and the rate of colour development.     

Responses of banana fruit to treatment with 1-methylcyclopropene

Experiments were conducted to determine levels of 1-methylcyclopropene (1-MCP) exposure needed to prevent ethylene-stimulated banana fruit ripening, characterise responses of ethylene-treated fruit to subsequent treatment with 1-MCP, and to test effects of subsequent ethylene treatment on 1-MCP-treated fruit softening. Fruit softening was measured at 20°C and 90% relative humidity. One hour exposure at 20°C to 1000 nl 1-MCP/l essentially eliminated ethylene-stimulated ripening effects. Exposure for 12 h at 20°C to just 50 nl 1-MCP/l was similarly effective. Fruit ripening initiated by ethylene treatment could also be delayed with subsequent 1-MCP treatment. However, 1-MCP treatment only slowed down ripening of ethylene-treated fruit when applied at 1 day after ethylene and was ineffective when applied 3 or 5 days after ethylene treatment. The ripening response of fruit treated with 1-MCP and subsequently treated with ethylene varied with interval time between 1-MCP and ethylene treatments. As time increased, the response of 1-MCP-treated fruit to ethylene was enhanced. Responses to 0.1, 1, 10 or 100 µl ethylene/l concentrations were similar. Enzyme kinetic analysis applied to 1-MCP effects on ethylene-induced softening of banana fruit suggested that 1-MCP inhibition is by noncompetitive antagonism of ethylene binding.