Ethylene sensitivity: The role of short-chain saturated fatty acids in pollination-induced senescence of Petunia hybrida flowers

Normal and pollination-induced senescence of Petunia hybrida L cv. Pink Cascade flowers is accompanied by an increase in the sensitivity of the corolla to ethylene as indicated by an acceleration in the rate of corolla bluing after exposure to exogenous ethylene. Pollination resulted in the production of short-chain saturated fatty acids ranging in chain length from C₆ to C₁₀. Following pollination, these acids are synthesized in the stylar tissue via the acetate pathway within the first 12 hours. The fatty acids are transported rapidly to the corolla where they induce an increase in ethylene sensitivity. In unpollinated flowers, these acids are produced in the corolla during the early stages of senescence. Although the levels of these fatty acids decrease rapidly during the final stages of senescence, a significant increase in ethylene sensitivity could be detected prior to the decrease. It appears that the increase in ethylene sensitivity caused by the synthesis of short-chain saturated fatty acids occurs concurrently, but independent from ethylene synthesis.     

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.     

Role of short-chain saturated fatty acids in the control of ethylene sensitivity in senescing carnation flowers

In cut carnations ( Dianthus caryophyllus L. cv. Cally). petal senescence was associated with a climacteric pattern in ethylene production and an increase in ethylene sensitivity during the preclimacteric stage. The increase in ethylene sensitivity was caused by short-chain saturated fatty acids (C₇ to C₁₀) produced in the petals during the early stages of senescence. Pollination or application of octanoic acid to the styles of unpollinated flowers resulted in a sudden increase in ethylene sensitivity and a marked acceleration of senescence. Treatment with silver thiosulfate (STS) resulted in a suppression of ethylene sensitivity and a marked reduction in the levels of these fatty acids. However, even in STS-treated flowers pollination or treatment with octanoic acid gave rise to a drastic increase in ethylene sensitivity. Exposure of carnation flowers to 2. 5-norbornadicne (NBD) vapours resulted in a dramatic suppression of ethylene sensitivity which was also overridden by stylar application of octanoic acid. Exposure to NBD suppressed the increase in ethylene sensitivity caused by treatment with octanoic acid. It appears that short-chain saturated fatty acids increased ethylene sensitivity by increasing the ability of the tissue to bind ethylene.     

The role of ethylene in the senescence of carnation flowers, a review

The senescence of flower petals is a highly regulated developmental process which requires active gene expression and protein synthesis. The biochemical changes associated with petal senescence in carnation flowers include an increase in hydrolytic enzymes, degradation of macro-molecules, increased respiratory activity and a climacteric-like increase in ethylene production. It is clear that the gaseous phytohormone ethylene plays a critical role in the regulation and coordination of senescence processes. Many reviews on physiology and mode of action of ethylene are available. Molecular cloning led to the isolation of genes involved in ethylene biosynthesis and action. This review describes the current status of the studies on regulation of ethylene biosynthesis and ethylene response in carnation flowers. An overview is given of studies on senescence-related gene expression and possibilities to improve postharvest longevity by genetic engineering.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AIB -amino-isobutyric acid - AOA amino oxyacetic acid - AVG aminoathoxyvinyl glycine - DACP diazocyclopentadiene - EFE ethylene forming enzyme - MACC malonyl 1-aminocyclopropane-1-carboxylic acid - MTA 5-methylthio-adenosine - NBD 2,5 norbornadiene - ppb parts per billion - SAM S-adenosyl-methionine - STS silver thiosulphate     

Enhancement of petunia and dendrobium flower senescence by jasmonic acid methyl ester is via the promotion of ethylene production

Methyl jasmonate (JA-Me), applied to dendrobium and petunia flowers either as an aqueous solution through the cut stem or stigma, or as a gas, accelerated senescence. The rate of appearance of wilting symptoms was directly related to the amount of JA-Me applied to the flowers. JA-Me increased ethylene production by the flowers, irrespective of application method, and this effect was also proportional to the dose of the compound. In both dendrobium and petunia flowers, the JA-Me induced increases in ethylene production and 1-aminocyclopropane-1-carboxylic acid content followed similar patterns. Aminooxyacetic acid, an inhibitor of ACC-synthase, and silver-thiosulfate, an inhibitor of ethylene action, completely inhibited the effects of JA-Me. It is concluded that JA-Me enhances petunia and dendrobium flower senescence via the promotion of ACC and ethylene production.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AOA aminooxyacetic acid - Fl flower - JA jasmonic acid - JA-Me jasmonic acid methyl ester - LOX lipoxygenase - PLase A A-type phospholipase - STS silver-thiosulfate     

Effects of 1,1-dimethyl-4-(phenylsulfonyl)semicarbazide (DPSS) on carnation flower longevity

The effects of a novel preservative for cut carnation flowers, 1,1-dimethyl-4-(phenylsulfonyl)semicarbazide (DPSS), were investigated. DPSS extended the vase life of cut carnation flowers not only by continuous treatment but pulse treatment as well. This inhibition of senescence by DPSS appeared to depend on that of ethylene production in carnation flowers. DPSS provided no protection from the action of ethylene nor did it inhibit 1-aminocyclopropane-1-carboxylic acid (ACC) synthase. It did inhibit ACC-dependent ethylene production in carnation petal discs, suggesting possible potential for inhibiting ACC oxidase.     

A flower senescence-related mRNA from carnation encodes a novel protein related to enzymes involved in phosphonate biosynthesis

We have isolated a cDNA clone (pSR132) representing a mRNA which accumulates in senescing carnation flower petals in response to ethylene. In vitro translation of RNA selected by hybridization with pSR132 indicated the mRNA encoded a polypeptide of approximately 36 kDa. This was confirmed by DNA sequence analysis, which predicted a peptide composed of 318 amino acids with a calculated molecular weight of 34.1 kDa. Comparison of the predicted peptide sequence of pSR132 with other proteins compiled in the NBRF data base revealed significant homology with carboxyphosphonoenolpyruvate mutase and phosphoenolpyruvate mutase from Streptomyces hygroscopicus and Tetrahymena pyriformis, respectively. These enzymes are involved in the formation of C-P bonds in the biosynthesis of phosphonates. C-P bonds are found in a wide range of organisms, but their presence or formation in higher plants has not been investigated.     

Cytokinins in cut carnation flowers. IV effects of benzyladenine on flower longevity and the role of different longevity treatments on its transport following application to the petals

A low concentration of benzyladenine (4.44 × 10^-5 M) accelerated the senescense of cut carnation flowers. This effect could be reversed by STS-treatment but not by keeping the flowers in a holding solution containing 4% ethanol. This appears to be the first report indicating that cytokinins at a specific level may actually enhance flower senescense. The higher levels tested (1.11 × 10^-4 and 2.22 × 10^-4 M) retarded senescense, being in agreement with published results. The applied cytokynin was metabolized slowly in the petals to a compound(s) which co-chromatographed with ribosylbenzyladenine when separated by TLC and when fractionated by HPLC. In the experiments applying (¹⁴C) benzyladenine to the petals, a small degree of transport of the ¹⁴C was detected in naturally senescing (control) cut flowers and when treated with ethrel. The transported ¹⁴C was detected in both the ovaries and in the stems and co-chromatographed with benzyladenine. Where flower senescense was delayed (ethanol or STS) no movement from the petals was detected. This suggests that the cytokinin moved within the assimilate stream, along with sugars.     

The effect of aminooxyacetic acid and cytokinin combinations on carnation flower longevity

A simplified method, which utilizes a 50% senescence value (S₅₀) for the measurement of longevity, in cut carnation flowers is used to compare flower longevity. A pulsed treatment using a combination of aminooxyacetic acid (AOA), kinetin and Triton X-100 enhanced flower vase-life relative to a water control. The mixture, however, did not exhibit synergistic effects when S₅₀ values of the individual compounds were compared. A single AOA pulse treatment was as effective as the mixture. These findings held true for three carnation cultivars. With the exception of dihydrozeatin, which greatly enhanced longevity, replacement of kinetin by a range of cytokinins did not produce significantly different results from the AOA/Triton X-100 combination. Holding solution treatments gave similar trends as pulse treatments. S₅₀ values were better units to express longevity than S₁₀₀ values.Abbreviations AOA aminooxyaceticacid - BA benzyladenine - S₅₀ 50% senescence value - STS silverthiosulphate - iP isopentenyladenize - Z zeatin - DHZ dihydrozeatin     

Changes of pH in <Emphasis Type="Italic">Petunia hybrida</Emphasis> (Hort.) styles induced by pollination and influence of proton pump and ion channels on its regulation

Ionselective microelectrode method was used to study changes of pH in transmitting tissue of style in Petunia hybrida (Hort.). Effect of pollination and pollen tube growth were examined. Subsequently solutions of ions and various stimulators or blockers of ion channels were applied on pollinated styles to examine the possible role of ion channels in pH stabilisation. It was confirmed in the present study that: (1) there is a pH gradient in the transmitting tissue of a petunia unpollinated style with the stigma region being more acidic; (2) pollination causes further acidification of transmitting tissue: (3) the gradient of pH first vanishes at 24 h after pollination then is reversed up to 72 h after pollination; (4) active transport of ions plays an important role in pH regulation in transmitting tissue. The presented results confirm the role of pH changes and Ca²⁺ as a mediator in controlling proton influx into the apoplast of the transmitting tissue during pollen tube growth.     

Pollination-induced senescence of Phalaenopsis petals

The longevity of cut Phalaenopsis (Phalaenopsis hybrid, cv. Herbet Hager) flowers is normally 2 to 3 weeks. After pollination however, there was a rapid acceleration of the wilting process, beginning after only 24 h. Enhancement of senescence in several Phalaenopsis cultivars as well as in Doritaenopsis, Dendrobium and Cymbidium, was induced by successful pollination and only slightly or not at all by emasculation. Wilting of the flowers was accompanied by a loss of water from cells of the upper layer of the petals, leading to their upward folding. Following pollination there was an increase in ethylene production and sensitivity to ethylene. The increase in ethylene production began about 10 h after pollination and reached its peak after 30 h. An obvious increase in sensitivity to ethylene could already be detected 4 h after pollination and reached its peak 10 h after pollination. The increase en ethylene sensitivity following pollination was not dependent on endogenous ethylene production as it occurred also in flowers treated with (aminooxy)acetic acid, an inhibitor of ethylene biosynthesis.Abbreviations AOA = (aminooxy)acetic acid - RH = relative humidity - SEM = scanning electron microscope     

Ethylene and flower petal senescence: Interrelationship with membrane lipid catabolism

Accumulated experimental evidence suggests that the decline in the content of membrane components such as phospholipids (PL), is a key event in flower senescence. This loss of membrane integrity can be modulated by ethylene. The aim of this work was to examine the interrelationship between ethylene and one of the products of PL metabolism, diacylglycerol (DAG), during petunia ( Petunia hybrida ) flower senescence. DAG's role was studied using phorbol 12-myristate 13-acetate (PMA), which acts similarly in kinase activation. Our results demonstrate for the first time a senescence-related transient increase in the content of DAG in petunia plasma membranes. The climacteric-like ethylene rise associated with petal wilting appeared in petunia flowers well after PL degradation and DAG increase had commenced. The appearance and peak magnitude of the ethylene rise was enhanced or increased, respectively, by PMA treatment, thereby accelerating appearance and magnitude of all senescence parameters assayed. Conversely, suppression of ethylene action by silver thiosulfate (STS) resulted in retardation of flower wilting, as well as in abolishment of the PMA-enhancing effects on senescence. The results suggest an active role for lipid metabolites like DAG in enhancing flower senescence, through regulation of ethylene production and action, or possible activation of kinases. This sequence of events implies that ethylene is a mediator of flower senescence, rather than a trigger of the process.     

Hormonal status of the pollen-pistil system at the progamic phase of fertilization after compatible and incompatible pollination in Petunia hybrida L.

The hormonal status of the pollen-pistil system in Petunia hybrida L. during the progamic phase of fertilization was investigated. The contents of indolyl-3-acetic acid (IAA), abscisic acid (ABA), and cytokinins, as well as the rate of ethylene production in the pistils and their parts (stigma, style, and ovary) were measured over an 8-h period following compatible and self-incompatible pollination. In both pollinations, the phytohormones were present in various proportions in the stigma, style and ovary: the stigma was the main site of ethylene synthesis and contained 90% of the ABA, while the style contained 80% of the total cytokinin content in the pollinated pistil. Relatively low levels of hormones in the ovary did not influence the hormonal status of the pollen-pistil system. The interaction of the male gametophyte with the stigmatic tissues was accompanied by a 7- to 10-fold increase in ethylene production and a 1.5- to 2.0-fold increase in IAA content in the pollen-pistil system over 0–4 h. Pollen tube growth after self-incompatible pollination, in contrast to compatible pollination, was accompanied by a 3-fold increase in the ABA content in the stigma and style and by a 5-fold higher cytokinin content in the stylar tissues. Thus, the ethylene/ABA status of the stigma may play a role in controlling the processes of adhesion, hydration, and germination of pollen grains during pollination while the auxin/cytokinin status of the style may be involved in controlling pollen tube growth.     

Senescence of cut carnation flowers: Ovary development and CO2 fixation

In the presence of ethylene, which enhances carnation flower senescence, carbohydrates contribute to ovary growth not only from the stem and calyx but also from the petals. With silver thiosulphate and ethanol treatments which delay flower senescence, the petals remain the active sink and ovary development is suppressed. Ethylene stimulated chloroplast development in the ovary wall. However, the calyx plus stem of all treatments showed the greater photosynthetic ability and transported a major portion of the synthesised products to the ovary.