Application Of 1-aminocyclopropane-1-carboxylic Acid Research Articles

GLABROUS INFLORESCENCE STEMS3 binds to and activates RHD2 and RHD4 genes to promote root hair elongation in Arabidopsis.

Root hairs are crucial in the uptake of essential nutrients and water in plants. This study showed that a zinc finger protein, GIS3 is involved in root hair growth in Arabidopsis. The loss-of-function gis3 and GIS3 RNAi transgenic line exhibited a significant reduction in root hairs compared to the wild type. The application of 1-aminocyclopropane-1-carboxylic acid (ACC), an exogenous ethylene precursor, and 6-benzyl amino purine (BA), a synthetic cytokinin, significantly restored the percentage of hair cells in the epidermis in gis3 and induced GIS3 expression in the wild type. More importantly, molecular and genetic studies revealed that GIS3 acts upstream of ROOT HAIR DEFECTIVE 2 (RHD2) and RHD4 by binding to their promoters. Furthermore, exogenous ACC and BA application significantly induced the expression of RHD2 and RHD4, while root hair phenotype of rhd2-1, rhd4-1, and rhd4-3 was insensitive to ACC and BA treatment. We can therefore conclude that GIS3 modulates root hair development by directly regulating RHD2 and RHD4 expression through ethylene and cytokinin signals in Arabidopsis.

Role of ethylene in effective establishment of the peanut-bradyrhizobia symbiotic interaction.

Ethylene has been implicated in nitrogen fixing symbioses in legumes, where rhizobial invasion occurs via infection threads (IT). In the symbiosis between peanut (Arachis hypogaea L.) and bradyrhizobia, the bacteria penetrate the root cortex intercellularly and IT are not formed. Little attention has been paid to the function of ethylene in the establishment of this symbiosis. The aim of this article is to evaluate whether ethylene plays a role in the development of this symbiotic interaction and the participation of Nod Factors (NF) in the regulation of ethylene signalling. Manipulation of ethylene in peanut was accomplished by application of 1-aminocyclopropane-1-carboxylic acid (ACC), which mimics applied ethylene, or AgNO3, which blocks ethylene responses. To elucidate the participation of NF in the regulation of ethylene signalling, we inoculated plants with a mutant isogenic rhizobial strain unable to produce NF and evaluated the effect of AgNO3 on gene expression of NF and ethylene responsive signalling pathways. Data revealed that ethylene perception is required for the formation of nitrogen-fixing nodules, while addition of ACC does not affect peanut symbiotic performance. This phenotypic evidence is in agreement with transcriptomic data from genes involved in symbiotic and ethylene signalling pathways. NF seem to modulate the expression of ethylene signalling genes. Unlike legumes infected through IT formation, ACC addition to peanut does not adversely affect nodulation, but ethylene perception is required for establishment of this symbiosis. Evidence for the contribution of NF to the modulation of ethylene-inducible defence gene expression is provided.

Molecular Mechanisms of the 1-Aminocyclopropane-1-Carboxylic Acid (ACC) Deaminase Producing Trichoderma asperellum MAP1 in Enhancing Wheat Tolerance to Waterlogging Stress.

Waterlogging stress (WS) induces ethylene (ET) and polyamine (spermine, putrescine, and spermidine) production in plants, but their reprogramming is a decisive element for determining the fate of the plant upon waterlogging-induced stress. WS can be challenged by exploring symbiotic microbes that improve the plant’s ability to grow better and resist WS. The present study deals with identification and application of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing fungal endophyte Trichoderma asperellum (strain MAP1), isolated from the roots of Canna indica L., on wheat growth under WS. MAP1 positively affected wheat growth by secreting phytohormones/secondary metabolites, strengthening the plant’s antioxidant system and influencing the physiology through polyamine production and modulating gene expression. MAP1 inoculation promoted yield in comparison to non-endophyte inoculated waterlogged seedlings. Exogenously applied ethephon (ET synthesis inducer) and 1-aminocyclopropane carboxylic acid (ACC; ET precursor) showed a reduction in growth, compared to MAP1-inoculated waterlogged seedlings, while amino-oxyacetic acid (AOA; ET inhibitor) application reversed the negative effect imposed by ET and ACC, upon waterlogging treatment. A significant reduction in plant growth rate, chlorophyll content, and stomatal conductance was noticed, while H2O2, MDA production, and electrolyte leakage were increased in non-inoculated waterlogged seedlings. Moreover, in comparison to non-inoculated waterlogged wheat seedlings, MAP1-inoculated waterlogged wheat exhibited antioxidant–enzyme activities. In agreement with the physiological results, genes associated with the free polyamine (PA) biosynthesis were highly induced and PA content was abundant in MAP1-inoculated seedlings. Furthermore, ET biosynthesis/signaling gene expression was reduced upon MAP1 inoculation under WS. Briefly, MAP1 mitigated the adverse effect of WS in wheat, by reprogramming the PAs and ET biosynthesis, which leads to optimal stomatal conductance, increased photosynthesis, and membrane stability as well as reduced ET-induced leaf senescence.

Zinc finger protein 5 (ZFP5) associates with ethylene signaling to regulate the phosphate and potassium deficiency-induced root hair development in Arabidopsis.

Zinc finger protein transcription factor ZFP5 positively regulates root hair elongation in response to Pi and potassium deficiency by mainly activating the expression of EIN2 in Arabidopsis. Phosphate (Pi) and potassium (K+) are major plant nutrients required for plant growth and development, and plants respond to low-nutrient conditions via metabolic and morphology changes. The C2H2 transcription factor ZFP5 is a key regulator of trichome and root hair development in Arabidopsis. However, its role in regulating root hair development under nutrient deprivations remains unknown. Here, we show that Pi and potassium deficiency could not restore the short root hair phenotype of zfp5 mutant and ZFP5 RNAi lines to wild type level. The deprivation of either of these nutrients also induced the expression of ZFP5 and the activity of an ethylene reporter, pEBS:GUS. The significant reduction of root hair length in ein2-1 and ein3-1 as compared to wild-type under Pi and potassium deficiency supports the involvement of ethylene in root hair elongation. Furthermore, the application of 1-aminocyclopropane-1-carboxylic acid (ACC) significantly enhanced the expression level of ZFP5 while the application of 2-aminoethoxyvinyl glycine (AVG) had the opposite effect when either Pi or potassium was deprived. Further experiments reveal that ZFP5 mainly regulates transcription of ETHYLENE INSENSITIVE 2 (EIN2) to control deficiency-mediated root hair development through ethylene signaling. Generally, these results suggest that ZFP5 regulates root hair elongation by interacting with ethylene signaling mainly through regulates the expression of EIN2 in response to Pi and potassium deficiency in Arabidopsis.

The involvement of jasmonates and ethylene in Alternaria alternata f. sp. lycopersici toxin-induced tomato cell death

Previous studies have shown that an ethylene (ET)-dependent pathway is involved in the cell death signalling triggered by Alternaria alternata f. sp. lycopersici (AAL) toxin in detached tomato (Solanum lycopersicum) leaves. In this study, the role of jasmonic acid (JA) signalling in programmed cell death (PCD) induced by AAL toxin was analysed using a 35S::prosystemin transgenic line (35S::prosys), a JA-deficient mutant spr2, and a JA-insensitive mutant jai1. The results indicated that JA biosynthesis and signalling play a positive role in the AAL toxin-induced PCD process. In addition, treatment with the exogenous ET action inhibitor silver thiosulphate (STS) greatly suppressed necrotic lesions in 35S::prosys leaves, although 35S::prosys leaflets co-treated with AAL toxin and STS still have a significant high relative conductivity. Application of 1-aminocyclopropane-1-carboxylic acid (ACC) markedly enhanced the sensitivity of spr2 and jai1 mutants to the toxin. However, compared with AAL toxin treatment alone, exogenous application of JA to the ET-insensitive mutant Never ripe (Nr) did not alter AAL toxin-induced cell death. In addition, the reduced ET-mediated gene expression in jai1 leaves was restored by co-treatment with ACC and AAL toxin. Furthermore, JA treatment restored the decreased expression of ET biosynthetic genes but not ET-responsive genes in the Nr mutant compared with the toxin treatment alone. Based on these results, it is proposed that both JA and ET promote the AAL toxin-induced cell death alone, and the JAI1 receptor-dependent JA pathway also acts upstream of ET biosynthesis in AAL toxin-triggered PCD.

Sensitivity and physiological responses of Eleusine indica and Digitaria adscendens to herbicide quinclorac and 2,4-D

The physiological responses of Eleusine indica (L.) Gaerth. and Digitaria adscendens (H.B.K.) Henr. seedlings to auxinic herbicides quinclorac (3,7-dichloro-8-quinolinecarboxylic acid) and 2,4-dichlorophenoxyacetic acid (2,4-D) were investigated to understand the differences in their phytotoxic actions and the tolerance mechanism of E. indica to quinclorac. Quinclorac (≤100 μM) had no effect on the seedling growth of E. indica, but 2,4-D (100 μM) inhibited the seedling growth of the plants. On the other hand, the seedling growth of D. adscendens was inhibited by both quinclorac (1–100 μM) and 2,4-D (100 μM). The chlorophyll content in E. indica shoots was not reduced by quinclorac (10 μM) treatment, but slightly reduced by 100 μM 2,4-D at 2 days after treatment. In D. adscendens seedlings, 10 μM quinclorac greatly reduced the chlorophyll content in the shoots at 2 days after treatment, whereas 100 μM 2,4-D did not affect the content. Moreover, 10 μM quinclorac did not induce ethylene production in E. indica but did so in D. adscendens seedlings. For 2,4-D treatment, the herbicide (100 μM) rapidly and strongly induced ethylene production in both E. indica and D. adscendens seedlings, although the level of 2,4-D-induced ethylene in E. indica was much higher than that in D. adscendens. In D. adscendens seedlings, ethylene production induced by quinclorac was less than by 2,4-D, whereas quinclorac induced a greater reduction in chlorophyll content in D. adscendens than 2,4-D. Application of 1-aminocyclopropane-1-carboxylic acid (ACC), an intermediate of ethylene biosynthesis, reduced root growth of E. indica and shoot growth of D. adscendens. Moreover, 10 μM quinclorac induced the formation of thiobarbituric acid-reactive substances (TBARS), an indicator of lipid peroxidation, in the shoots of D. adscendens but not in E. indica. However, 100 μM 2,4-D did not induce TBARS formation in either E. indica or D. adscendens, whereas the herbicide inhibited seedling growth in both plants. These results show that E. indica is tolerant to quinclorac and susceptible to 2,4-D, and D. adscendens is susceptible to both quinclorac and 2,4-D. The phytotoxic actions of quinclorac and 2,4-D on D. adscendens seem to be related to the ethylene biosynthetic pathway. However, the present results also suggest that quinclorac has additional oxidative actions resulting in chlorosis and lipid peroxidation in D. adscendens.

Ethylene regulates lateral root formation and auxin transport in Arabidopsis thaliana

Lateral root branching is a genetically defined and environmentally regulated process. Auxin is required for lateral root formation, and mutants that are altered in auxin synthesis, transport or signaling often have lateral root defects. Crosstalk between auxin and ethylene in root elongation has been demonstrated, but interactions between these hormones in the regulation of Arabidopsis lateral root formation are not well characterized. This study utilized Arabidopsis mutants altered in ethylene signaling and synthesis to explore the role of ethylene in lateral root formation. We find that enhanced ethylene synthesis or signaling, through the eto1-1 and ctr1-1 mutations, or through the application of 1-aminocyclopropane-1-carboxylic acid (ACC), negatively impacts lateral root formation, and is reversible by treatment with the ethylene antagonist, silver nitrate. In contrast, mutations that block ethylene responses, etr1-3 and ein2-5, enhance root formation and render it insensitive to the effect of ACC, even though these mutants have reduced root elongation at high ACC doses. ACC treatments or the eto1-1 mutation significantly enhance radiolabeled indole-3-acetic acid (IAA) transport in both the acropetal and the basipetal directions. ein2-5 and etr1-3 have less acropetal IAA transport, and transport is no longer regulated by ACC. DR5-GUS reporter expression is also altered by ACC treatment, which is consistent with transport differences. The aux1-7 mutant, which has a defect in an IAA influx protein, is insensitive to the ethylene inhibition of root formation. aux1-7 also has ACC-insensitive acropetal and basipetal IAA transport, as well as altered DR5-GUS expression, which is consistent with ethylene altering AUX1-mediated IAA uptake, and thereby blocking lateral root formation.

Molecular characterization and expression analysis of 1-aminocyclopropane-1-carboxylate oxidase homologs from potato under abiotic and biotic stresses.

In this work, we report cloning of two full-length 1-aminocyclopropane-1-carboxylate oxidase (ACO) cDNAs (ACO1 and ACO2) from potato (Solanum tuberosum) and their expression in potato tissues. The sequence data indicate that the two cDNAs share a high degree of homology with each other, and with known ACO genes from other plant species, including monocots and dicots. However, these potato genes lack homology at the 5' and 3' ends, despite similarities in their open reading frames and encoded amino acids. Phylogenetic analysis places them in two subfamilies of ACOs. The genes are tissue specific: expression is high in leaves and low in roots and tubers. In sprouts and tubers, ACO1 is induced by heat (40 degrees C) and cold (0 degrees C) stresses, whereas ACO2 is induced only by cold (0 degrees C). ACO1 is markedly induced in leaves by wounding, soil-flooding, and exogenous application of 1-aminocyclopropane-1-carboxylic acid (ACC). In contrast, ACO2 induction is lower under these treatments. ACO1 and ACO2 are regulated very differently in potato leaves with respect to senescence. ACO2 expression is unaffected by senescence, whereas that of ACO1 is closely related to the age and senescence in both attached and detached leaves. Exogenous ACC not only induces ACO1, but also accelerates leaf senescence. ACO1 transcripts are induced significantly in leaves, stems, and tubers in the Potato virus A (PVA)-resistant potato cultivar Shepody when graft inoculated with PVA.

Ethylene production and post-pollination development in Dendrobium flowers treated with foreign pollen

Dendrobium ‘Pompadour’ flowers fade early following pollination. This is associated with increased ethylene production and early epinasty. These effects are also produced by application of 1-aminocyclopropane-1-carboxylic acid (ACC) on the stigma. Pollen (one anther each) from Ruellia tuberosa L. (Acanthaceae) and Caesalpinia pulcherrima (L.) Sw. (Fabaceae) also increased ethylene production and caused early epinasty and fading. Pollen of Hibiscus schizopetalus (Mast.) Hook.f. (Malvaceae), in contrast, had no effect. R. tuberosa pollen increased ACC concentration and ACC synthase activity of the orchid flowers. Aminooxyacetic acid (AOA) pretreatment prior to R. tuberosa pollination prevented early fading, epinasty and the increase in ethylene production. It also prevented the increase in ACC concentration, and ACC synthase activity. Ovary growth was stimulated by Dendrobium ‘Pompadour’ pollinia, not by any of the incompatible pollen. Applied ACC did not promote ovary growth. It is concluded that incompatible pollen can hasten senescence and epinasty by increasing ACC synthase activity and ethylene production. Ovary growth, in contrast, is apparently not primarily regulated by ethylene.

Regulation of pollination‐induced ethylene and its role in petal abscission of Pelargonium×hortorum

Pollination in geranium (Pelargonium×hortorum) results in rapid non‐autocatalytic ethylene production followed by abscission of turgid petals. In the present work, the regulation of post‐pollination ethylene was investigated in various floral organs. Ethylene production and petal abscission increased as the number of stigmatic lobes pollinated increased. Direct application of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) to the stigma induced ethylene production and petal abscission only at high concentrations, which are not naturally present in the pollen. Application of aminoethoxyvinylglycine (AVG), an inhibitor of ACC synthase activity, to the stigma effectively prevented pollination‐induced ethylene production and petal abscission. Pollination increased the levels of ACC 46‐fold in stigma plus style tissue and 6‐fold in the basal portion of petals. Enhanced accumulation of N‐malonyl‐ACC (MACC), a conjugated form of ACC, was also observed in stigma and style tissues after pollination. Pollination increased the activity of ACC synthase 2.5‐fold in stigma and style tissues and 3‐fold in the basal portion of petals. At 2 h after pollination, a 4‐fold increase in the expression of the ACC synthase gene GAC‐1 was detected specifically in the stigma and style. In vivo activity of ACC oxidase was 1.5‐fold higher in pollinated than in unpollinated or wounded stigma and style. In the lower part of the pistil, the activity of ACC oxidase was lower than in the upper pistil, regardless of treatment. The activity of ACC oxidase was significantly higher in the basal portion of petals than the upper portion of petals. Pollination had no effect on the activity of ACC oxidase in petals. Treatment of florets with cycloheximide effectively prevented pollination‐induced petal abscission, but ethylene production was completely unaffected, providing evidence for the post‐transcriptional regulation of ethylene production. Stigma and style tissues accounted for 57% of the total ethylene production in the flower following pollination. When the stigma and style were removed and the top of the sterile ovary pollinated, there was no pollination‐induced ethylene production or petal abscission. We propose that rapid petal abscission in response to pollination results from increased ethylene production, which occurs via activation of ACC synthase primarily in the stigma and style. This contrasts with post‐pollination ethylene production in some wilting‐type flowers in timing, lack of autocatalytic ethylene and predominantly post‐transcriptional regulation.

Ethylene‐induced putrescine accumulation modulates K+ partitioning between roots and shoots in barley seedlings

We investigated the cause and effect relationships among ethylene, polyamines, and K+ in barley (Hordeum vulgare L. cv. Amagi) seedlings. Application of 1‐aminocyclopropane‐1‐carboxylic acid (ACC), a precursor of ethylene, to the growth medium caused a decrease in K+ concentration in roots and an increase in shoots. Addition of ACC induced putrescine accumulation in roots, while spermidine and spermine levels remained unchanged. Exogenous supply of putrescine led to putrescine accumulation and reduced K+ concentration. Application of Co2+, an inhibitor of ethylene biosynthesis, together with ACC, inhibited putrescine accumulation with a decrease in K+ concentration in roots. ACC‐treated roots showed K+ uptake capacity equivalent to that of control roots, implying that the majority of K+ is translocated to shoots. These results suggest that ethylene regulates K+ partitioning between roots and shoots through the level of accumulation of putrescine in barley seedlings.

Acetaldehyde inhibition of ethylene biosynthesis in mango fruit

Abstract Mango fruit ripening is accompanied by increased ethylene production which coordinates the ripening process. Ethylene production in other fruit has been shown to be inhibited by acetaldehyde and ethanol. In unripe mango fruit the ethylene production is very low ( −1 h −1 ) and treatments with acetaldehyde and ethanol had concentration-dependent effects on ethylene production. The application of 1-aminocyclopropane-1-carboxylic acid (ACC) to acetaldehyde or ethanol treated fruit discs showed acetaldehyde to be capable of completely eliminating increased ACC oxidase activity, whereas ethanol did not. This suggests that acetaldehyde is capable of inhibiting the activity of ACC oxidase directly, or alternatively of preventing the increase in the enzyme, thereby providing a possible mechanism for retarding fruit ripening.

Abscission of Flower Peduncles in Rose ( Rosa × hybrida) Plants and Evolution of Ethylene

Summary Ethylene evolution from decapitated rose ( Rosa × hybrida cv. Nubia) peduncles in planta and explants showed a climacteric pattern typical of abscising plant organs. The rate of ethylene evolution from nondecapitated explants was higher than that from decapitated ones and was the highest from separated flower buds. Local application of IAA at the site of bud removal postponed abscission of decapitated peduncles by 10 days in comparison with decapitated peduncles without IAA. The inhibition of abscission with IAA was accompanied by an earlier and higher rise in ethylene evolution and by yellowing of the peduncles; basal application of STS (silver thiosulphate) postponed the abscission of decapitated peduncles for a period longer than 6 weeks without any visible symptoms of senescence and was also associated with increased evolution of ethylene. Application of 1-aminocyclopropane-1-carboxylic acid (ACC) stimulated evolution of ethylene and promoted abscission of non-decapitated and decapitated peduncles, as well as of peduncles treated with IAA, but did not affect the STS-imposed inhibition of peduncle abscission. An extremely high rise in ethylene was measured without affecting abscission when STS and IAA treatments were combined. The role of auxin in context of the concept of «tissue sensitivity» to ethylene is discussed. A possible existence of two separate ethylene systems, one involved in regulation of flower bud development and the second in regulation of flower bud and leaf absiccion, is discussed.

Effect of wounding on ethylene biosynthesis and senescence of detached spinach leaves

Parameters of senescence and ethylene biosynthesis pathway were screened simultaneously in detached spinach leaves and leaf discs. Senescence was enhanced by application of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and was retarded by amino‐ethoxyvinylglycine (AVG). Evidence is presented showing that the bursts of both wound‐ and climacteric‐like ethylene promoted senescence of detached leaves and leaf discs. This ethylene‐enhanced leaf senescence was dependent on: (a) ethylene production rates in the tissue; (b) the degree of wounding. Wounding resulted in elevated levels of 1‐(malonylamino)cyclopropane‐1‐carboxylic acid (MACC), which declined in advanced stages of senescence. The results suggest that wounding might be regarded as one of the primary events in the induction of the senescence syndrome in detached leaves and leaf discs, while ethylene is implicated as a regulator of the rate of the process.

HEAT TOLERANCE AND ETHYLENE PRODUCTION IN RED-OSIER DOGWOOD STEM TISSUES AT DIFFERENT GROWTH STAGES

Red-osier dogwood sterns, Cornus sericea L., at ten different growth stages were subjected to a series of temperatures ranging from 25C to 60C by immersing them in a water bath for one hour. After heat treatments, the viability of internode tissues were determined by electrical conductivity and ethylene production. Heat tolerance was expressed as LT50, the temperature at which 50% of the tissues were injured. The results suggest that the LT50 of dormant plants remained relatively constant, approximately 53C. During dormancy, heat stress did not stimulate ethylene production from internode tissues. In contrast, tissues from non-dormant plants exposed to heat stress produced increasing levels of ethylene reaching a peak at 40C followed by a steady decrease at higher temperatures. Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to stem segments from dormant plants, following heat treatment, enhanced production of ethylene.

The Control of Flower Senescence in Petunia (Petunia hybrids)

Petunia corollas wilt and abscise between one and two weeks after detachment when maintained in distilled water in vials at 18 °C. The onset of wilting is brought forward substantially by the application of 1-aminocyclopropane-1-carboxylic acid (ACC) either to the vial solution or to the stigmatic surface. Both pollination and stigma removal also shorten the time to the onset of wilting, colour change and to abscission. In the case of stigma removal, the life span of the corolla is shortest when the treatment is made at the time of flower detachment (day 0), whereas pollination has the greatest effect if it occurs on day 1. Stigma damage still has an effect on corolla senescence even when stigma and style are removed, as long as they have been left in place for a few hours after treatment. Evidence from several experiments shows that a 17 h period is sufficient for the full effect to be shown, and that probably there are some effects on the corolla even if the damaged stigma is only left in position for 3–6 h. Treatments which advance corolla death (to day 3) also advance the peak of ethylene production by the pistil (to day 1) and the corolla (to day 2). The use of silver thiosulphate (STS) overcomes all manipulative and chemical treatments used, and greatly extends vase life. The extension occurs even when STS application is delayed for 24 h, i.e. after the peak of ethylene production by the pistil and after any senescence signal has arrived at the corolla. In this case, however, the time to first morphological change is largely unaffected, but the STS greatly extends the time period between first morphological change and corolla death. The evidence suggests that early symptoms of senescence e.g. colour change and slight loss of turgor, do not automatically lead to corolla abscission.

Role of Ethylene in the Senescence of Isolated Hibiscus Petals

Senescence of petals isolated from flowers of Hibiscus rosa-sinensis L. (cv Pink Versicolor) was associated with increased ethylene production. Exposure to ethylene (10 microliters per liter) accelerated the onset of senescence, as indicated by petal in-rolling, and stimulated ethylene production. Senescence was also hastened by basal application of 1-aminocyclopropane-1-carboxylic acid (ACC). Aminooxyacetic acid, an inhibitor of ethylene biosynthesis, effectively inhibited ethylene production by petals and delayed petal in-rolling. In marked contrast to these results with mature petals, immature petals isolated from flowers the day before flower opening did not respond to ethylene in terms of an increase in ethylene production or petal in-rolling. Furthermore, treatment with silver thiosulfate the day before flower opening effectively prevented petal senescence, while silver thiosulfate treatment on the morning of flower opening was ineffective. Application of ACC to both immature and mature petals greatly stimulated ethylene production indicating the presence of an active ethylene-forming enzyme in both tissues. Immature petals contained less free ACC than mature, presenescent petals and appeared to possess a more active system for converting ACC into its conjugated form. Thus, while the nature of the lack of responsiveness of immature petals to ethylene is unknown, ethylene production in hibiscus petals appears to be regulated by the control over ACC availability.

1-aminocyclopropane-l-carboxylic acid (ACC)—The transmitted stimulus in pollinated flowers?

Ethylene production and senescence of petals of pollinated carnation flowers were not prevented by removal of the ethylene produced by the gynoecium, suggesting that these events are a response to movement from the gynoecium of some stimulus other than ethylene gas. Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to the stigmas caused an initial increase in gynoecium and petal ethylene production similar to that reported for pollinated flowers. This response was not seen in flowers whose stigmas were treated with indoleacetic acid (IAA). When [2-14C]ACC was applied to the stigmas of carnation flowers, radioactive ethylene was produced both by the gynoecia and by the petals. The possibility that ACC, transported from the stigmas to the petals, is responsible for the postpollination changes in carnation flowers is discussed.

Wound-induced Ethylene Formation in Albedo Tissue of Citrus Fruit

Excised albedo tissue of citrus fruit (Citrus unshiu and Citrus hassaku) produced ethylene at an increasing rate in response to wounding and aging. The application of 1-aminocyclopropane-1-carboxylic acid (ACC) enhanced ethylene production in both the fresh and aged tissues, but this increase was greater in the aged tissue than in the fresh tissue. ACC content was very low in fresh tissue but increased greatly in aging tissue, paralleling the rise in ethylene production. Aminoethoxyvinylglycine (AVG) strongly inhibited ethylene production in the aged tissue. In the presence of ACC, however, ethylene production was not inhibited by AVG. These results suggest that ACC is an intermediate in the pathway of ethylene biosynthesis in the albedo tissue and that both steps of ACC formation and ACC conversion to ethylene are enhanced by wounding and aging. Inhibitors of protein synthesis, cycloheximide and 2-(4-methyl-2,6-dinitroanilino)-N-methyl propionamide, strongly inhibited ethylene production in the albedo tissue, implying that protein synthesis is required to maintain the continuous evolution of ethylene. The stimulation of ethylene production by ACC was reduced by the addition of l-methionine, whereas d-methionine had very little inhibitory effect. Ethylene production in the albedo tissue was also inhibited by the addition of n-propyl gallate and 3,5-dibromo-4-hydroxybenzoic acid.

Effect of 1-Aminocyclopropane-1-Carboxylic Acid on the Production of Ethylene in Senescing Flowers of Ipomoea tricolor Cav.

Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to rib segments excised from flowers of Ipomoea tricolor Cav. resulted in the formation of C(2)H(4) in greater quantities than produced under natural conditions. The ability of ACC to enhance C(2)H(4) production was independent of the physiological age of the tissue and its capacity to synthesize C(2)H(4) without applied ACC. When ACC was fed to rib segments that had been treated with [(14)C]methionine, incorporation of radioactivity into C(2)H(4) was reduced by 80%. Aminoethoxyvinylglycine and aminooxyacetic acid inhibited C(2)H(4) production in rib segments of I. tricolor but had no effect on ACC-enhanced C(2)H(4) production. Protoplasts obtained from flower tissue of I. tricolor did not form C(2)H(4), even when incubated with methionine or selenomethionine. They produced C(2)H(4) upon incubation with ACC, however. ACC-dependent C(2)H(4) production in protoplasts was inhibited by n-propyl gallate, AgCl, CoCl(2), KCN, Na(2)S, and NaN(3). ACC-dependent C(2)H(4) synthesis in rib segments and protoplasts was dependent on O(2), the K(m) for O(2) being 1.0 to 1.4% (v/v). These results confirm the following pathway for C(2)H(4) biosynthesis in I. tricolor. methionine [selenomethionine] --> S-adenosylmethionine [selenoadenosylmethionine] --> ACC --> C(2)H(4).