Ethylene Antagonist Research Articles

Ethylene is critical to the maintenance of primary root growth and Fe homeostasis under Fe stress in Arabidopsis.

Iron (Fe) is an essential microelement but is highly toxic when in excess. The response of plant roots to Fe toxicity and the nature of the regulatory pathways engaged are poorly understood. Here, we examined the response to excess Fe exposure in Arabidopsis wild type and ethylene mutants with a focus on primary root growth and the role of ethylene. We showed that excess Fe arrested primary root growth by decreasing both cell elongation and division, and principally resulteds from direct external Fe contact at the root tip. Pronounced ethylene, but not abscisic acid, evolution was associated with excess Fe exposure. Ethylene antagonists intensified root growth inhibition in the wild type, while the inhibition was significantly reduced in ethylene-overproduction mutants. We showed that ethylene plays a positive role in tissue Fe homeostasis, even in the absence of iron-plaque formation. Ethylene reduced Fe concentrations in the stele, xylem, and shoot. Furthermore, ethylene increased the expression of genes encoding Fe-sequestering ferritins. Additionally, ethylene significantly enhanced root K(+) status and upregulated K(+)-transporter (HAK5) expression. Our findings highlight the important role of ethylene in tissue Fe and K homeostasis and primary root growth under Fe stress in Arabidopsis.

Hormonal interactions during cluster-root development in phosphate-deficient white lupin (Lupinus albus L.)

This study addresses hormonal interactions involved in cluster-root (CR) development of phosphate (Pi)-deficient white lupin (Lupinus albus), which represents the most efficient plant strategy for root-induced mobilisation of sparingly soluble soil phosphorus (P) sources.Shoot-to-root translocation of auxin was unaffected by P-limitation, while strong stimulatory effects of external sucrose on CR formation, even in P-sufficient plants, suggest sucrose, rather than auxins, acts as a shoot-borne signal, triggering the induction of CR primordia. Ethylene may act as mediator of the sucrose signal, as indicated by moderately increased expression of genes involved in ethylene biosynthesis in pre-emergent clusters and by strong inhibitory effects of the ethylene antagonist CoCl2 on CR formation induced by sucrose amendments or P-limitation. As reported in other plants, moderately increased production of brassinosteroids (BRs) and cytokinin, in pre-emergent clusters, may be required for the formation of auxin gradients necessary for induction of CR primordia via interference with auxin biosynthesis and transport. The well-documented inhibition of root elongation by high doses of ethylene may be involved in the growth inhibition of lateral rootlets during CR maturation, indicated by a massive increased expression of gene involved in ethylene production, associated with a declined expression of transcripts with stimulatory effects (BR and auxin-related genes).

Ethylene Biosynthetic Responses of Mango (Mangifera indica L. cv. ‘Carabao’) Fruits to 1-methylcyclopropene (1-MCP) Preharvest Aqueous Spray Applications

800x600 The ethylene antagonist 1-methylcyclopropene (1-MCP) was used as a tool to investigate the mechanism of ethylene feedback regulation in mango (Mangifera indica L. cv. ‘Carabao’) fruits. The ethylene biosynthetic responses of mango fruits to 1-MCP applied prior the upsurge in ethylene production on-tree which was around 100 days after flower induction (DAFI) were studied. Aqueous 1-MCP spray formulation with 10 ppm concentration was applied to on-tree mango fruits at 100 DAFI. From these sprayed fruits, four (4) sets of fruits were tagged for a second round of 10 ppm aqueous 1-MCP spraying. One set was sprayed the second time at 105 DAFI, while the remaining sets at 110, 115 and 120 DAFI respectively. The positive control was sprayed with 0 ppm 1-MCP while the negative controls were the unsprayed fruits. Representative fruit samples from each set were harvested 2 d after spraying and every 2 d thereafter until reaching 120 DAFI. Right after each harvest, samples were analyzed for internal ethylene, ethylene production, ACC levels and ACC oxidase activities. The negative control exhibited two internal ethylene peaks before harvest maturity. However, in 1-MCP treated fruits, low levels of ethylene were detected and the second peak was not observed. A single application of 1-MCP at 100 DAFI resulted in lower ethylene production compared with controls. However, a second application proved to be more effective as the lowering of ethylene production was carried over until the day of harvest. The levels of 1-aminocyclopropane-1-carboxylate (ACC) increased after 110 DAFI for the controls. Reapplication of 1-MCP at 110 DAFI resulted to lower ACC levels, which was not observed with the other treatments with 1-MCP reapplication. Possibly, new ethylene receptors are synthesized at 110 DAFI, and 1-MCP reapplication at this time effectively blocks ethylene binding to the new receptors. ACC oxidase activity was lowered by 1-MCP applied at 100 DAFI compared with the controls. However, trends in ACC oxidase activities were almost the same for all the treatments and controls after 105 DAFI. Thus, ACC oxidase proceeds with its normal activity without being inhibited by 1-MCP. This suggests that ethylene biosynthesis in ‘Carabao’ mango fruit is regulated at the level of ACC synthase and not ACC oxidase. Thus, autocatalytic ethylene biosynthesis in ‘Carabao’ mango can be controlled by regulating ACC synthase activity, which proves that ACC synthesis is the rate limiting step in ethylene feedback mechanism in ‘Carabao’ mango. Normal 0 false false false EN-PH X-NONE X-NONE

The novel ethylene antagonist, 3-cyclopropyl-1-enyl-propanoic acid sodium salt (CPAS), increases grain yield in wheat by delaying leaf senescence

The present report describes the effect of 3-cyclopropyl-1-enyl-propanoic acid sodium salt (CPAS—WO 2010/0822930), a novel water soluble ethylene antagonist, on senescence and grain yield of several cultivars of common wheat (Triticum aestivum L.) and durum wheat (T. durum Desf.). CPAS abolished ethylene-induced leaf and ear organ senescence, as evidenced by the inhibition of chlorophyll degradation. CPAS application to wheat plants grown under controlled (120 mg L−1) or field conditions (110 mg L−1) significantly increased grain yield in the range of 9–13 % and 3–45 %, respectively, depending on treatment and variety. The CPAS-induced increase in grain yield was usually more significant under extreme weather conditions. In some cases spraying once at the medium milk stage was sufficient to obtain the maximum increase in grain yield, while in other cases spraying twice at the medium and late milk stages yielded the highest increase. The above data support the common view, that there is a positive causal relationship between the delay of leaf and ear organ senescence and grain yield. The results of the present study demonstrate that CPAS can effectively be used to increase wheat grain yield, and possibly the yield of other field crops, under field conditions.

Morphological and molecular characterization of ethylene binding inhibition in carnations

Ethylene perception by ethylene receptors can be suppressed by ethylene antagonists, such as 1-methylcyclopropene (1-MCP). 1-MCP binds to ethylene receptors blocking ethylene binding, and thereby represses ethylene responses, including flower senescence and petal abscission. Despite its antagonistic propensity, plants treated with 1-MCP often regain sensitivity to ethylene, suggesting that ethylene receptors are synthesized de novo post-treatment. To investigate this observation, we determined the relationship between the mRNA levels of ethylene biosynthesis and ethylene receptor genes and the degree of ethylene sensitivity of carnation flowers after ethylene and 1-MCP treatments. Flowers treated with a single application of 1-MCP lost the inhibitory effect in ethylene production after 7d of the treatment. In contrast, multiple treatments with 1-MCP completely suppressed several ethylene biosynthesis genes and ethylene production throughout the experiment. Multiple 1-MCP treatments increased vase life by almost three-fold relative to control flowers. Eventually ethylene-independent browning and desiccation on the edges of petals contributed to loss of vase life. We observed that the transcript levels of the ethylene receptor genes, DcETR1 and DcERS1, decreased with flower development, but increased at the onset of floral senescence. Our results suggest that ethylene receptors are continually synthesized during later stages of floral development. While ethylene responsiveness is temporarily blocked by 1-MCP treatment, we predict that new receptors synthesized days after 1-MCP treatment can bind ethylene. This leads to the observed recovery of ethylene sensitivity in the flowers. In addition, we predict that the degradation of ethylene receptors that is stimulated by ethylene binding is prevented by successive treatments with 1-MCP prior to recovery of ethylene sensitivity. This study improves our understanding about the uses and effectiveness of 1-MCP and will facilitate the development and improvement of postharvest treatments for multiple crops.

The effects of ethylene, 1-MCP and AVG on sprouting in sweetpotato roots

Exogenous ethylene is commonly used as a commercial sprouting inhibitor of potato tubers. The role of ethylene in the control of sprouting of sweetpotato roots, however, is not known. The aim of this study was to investigate the role of ethylene in control of sprouting in sweetpotato roots by observing the effect of an ethylene synthesis inhibitor, aminoethoxyvinylglycine (AVG), and the ethylene antagonist, 1-methylcyclopropene (1-MCP), in the presence and absence of exogenous ethylene on root sprouting and associated sugar accumulation. Continuous exposure to 10μlL−1 ethylene, 24h exposure to 625nlL−1 1-MCP or dipping in 100μlL−1 AVG all inhibited sprout growth in sweetpotato roots of two varieties over 4 weeks of storage at 25°C. The observations that both ethylene on its own and 1-MCP, which inhibits ethylene action, inhibit sprout growth indicate that while continuous exposure to exogenous ethylene leads to sprout growth inhibition, ethylene is also required for sprouting. In potato tubers ethylene is required to break dormancy, while continuous exposure inhibits sprout growth.Monosaccharide concentrations in ethylene, 1-MCP or AVG treated roots were lower than in untreated roots, and for ethylene treated roots this was associated with higher respiration rates. This is consistent with the activation of some additional process by ethylene which uses energy through sugar metabolism. 1-MCP and AVG both inhibited this increase in respiration rate and counteracted the decrease in monosaccharide concentrations. 1-MCP presumably counteracts the ethylene stimulation of this process, while the effect of AVG is attributed to its possible inhibitory effects on protein synthesis.

Ammonium-induced shoot ethylene production is associated with the inhibition of lateral root formation in Arabidopsis

Foliar NH4(+) exposure is linked to inhibition of lateral root (LR) formation. Here, the role of shoot ethylene in NH4(+)-induced inhibition of LR formation in Arabidopsis was investigated using wild-type and mutant lines that show either blocked ethylene signalling (etr1) or enhanced ethylene synthesis (eto1, xbat32). NH4(+) exposure of wild-type Arabidopsis led to pronounced inhibition of LR production chiefly in the distal root, and triggered ethylene evolution and enhanced activity of the ethylene reporter EBS:GUS in the shoot. It is shown that shoot contact with NH4(+) is necessary to stimulate shoot ethylene evolution. The ethylene antagonists Ag(+) and aminoethoxyvinylglycine (AVG) mitigated LR inhibition under NH4(+) treatment. The decrease in LR production was significantly greater for eto1-1 and xbat32 and significantly less for etr1-3. Enhanced shoot ethylene synthesis/signalling blocked recovery of LR production when auxin was applied in the presence of NH4(+) and negatively impacted shoot AUX1 expression. The findings highlight the important role of shoot ethylene evolution in NH4(+)-mediated inhibition of LR formation.

Plan B for Stimulating Stem Cell Division

Plan B for Stimulating Stem Cell Division

Delay of Iris flower senescence by cytokinins and jasmonates

It is not known whether tepal senescence in Iris flowers is regulated by hormones. We applied hormones and hormone inhibitors to cut flowers and isolated tepals of Iris × hollandica cv. Blue Magic. Treatments with ethylene or ethylene antagonists indicated lack of ethylene involvement. Auxins or auxin inhibitors also did not change the time to senescence. Abscisic acid (ABA) hastened senescence, but an inhibitor of ABA synthesis (norflurazon) had no effect. Gibberellic acid (GA3 ) slightly delayed senescence in some experiments, but in other experiments it was without effect, and gibberellin inhibitors [ancymidol or 4-hydroxy-5-isopropyl-2-methylphenyltrimethyl ammonium chloride-1-piperidine carboxylate (AMO-1618)] were ineffective as well. Salicylic acid (SA) also had no effect. Ethylene, auxins, GA3 and SA affected flower opening, therefore did reach the flower cells. Jasmonates delayed senescence by about 2.0 days. Similarly, cytokinins delayed senescence by about 1.5-2.0 days. Antagonists of the phosphatidylinositol signal transduction pathway (lithium), calcium channels (niguldipine and verapamil), calmodulin action [fluphenazine, trifluoroperazine, phenoxybenzamide and N-(6-aminohexyl)-5-chloro-1-naphtalenesulfonamide hydrochloride (W-7)] or protein kinase activity [1-(5-isoquinolinesulfonyl)-2-methylpiperazine hydrochloride (H-7), N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide hydrochloride (H-8) and N-(2-aminoethyl)-5-isoquinolinesulfonamide dihydrochloride (H-9)] had no effect on senescence, indicating no role of a few common signal transduction pathways relating to hormone effects on senescence. The results indicate that tepal senescence in Iris cv. Blue Magic is not regulated by endogenous ethylene, auxin, gibberellins or SA. A role of ABA can at present not be excluded. The data suggest the hypothesis that cytokinins and jasmonates are among the natural regulators.

INVESTIGATIONS INTO THE MOLECULAR AND PHYSIOLOGICAL FACTORS INFLUENCING LOW TEMPERATURE BREAKDOWN IN STONEFRUIT

Cold storage is essential for the successful distribution of stonefruit to distant markets; however most cultivars suffer chilling injury (CI), commonly referred to as low temperature breakdown (LTB). LTB is a significant problem for industry and the genetic factors responsible for its onset are not understood. Treatment of stonefruit with the ethylene antagonist, 1-methylcyclopropene (1-MCP) before cold storage has been shown to differentially affect the development of CI in peaches and plums. 1-MCP treatment increases the incidence of LTB in peaches but reduces it in plums (Fernandez-Trujillo and Artes, 1997; Fan et al., 2002). These observations were confirmed and preliminary research into the effects of 1-MCP and cold storage on gene expression is reported herein.

Ligand-Induced Alterations in the Phosphorylation State of Ethylene Receptors in Tomato Fruit

Perception of the plant hormone ethylene is essential to initiate and advance ripening of climacteric fruits. Since ethylene receptors negatively regulate signaling, the suppression is canceled upon ethylene binding, permitting responses including fruit ripening. Although receptors have autophosphorylation activity, the mechanism whereby signal transduction occurs has not been fully determined. Here we demonstrate that LeETR4, a critical receptor for tomato (Solanum lycopersicum) fruit ripening, is multiply phosphorylated in vivo and the phosphorylation level is dependent on ripening stage and ethylene action. Treatment of preclimacteric fruits with ethylene resulted in accumulation of LeETR4 with reduced phosphorylation whereas treatments of ripening fruits with ethylene antagonists, 1-methylcyclopropene and 2,5-norbornadiene, induced accumulation of the phosphorylated isotypes. A similar phosphorylation pattern was also observed for Never ripe, another ripening-related receptor. Alteration in the phosphorylation state of receptors is likely to be an initial response upon ethylene binding since treatments with ethylene and 1-methylcyclopropene rapidly influenced the LeETR4 phosphorylation state rather than protein abundance. The LeETR4 phosphorylation state closely paralleled ripening progress, suggesting that the phosphorylation state of receptors is implicated in ethylene signal output in tomato fruits. We provide insights into the nature of receptor on and off states.

Recombinant monoclonal antibody yield in transgenic tobacco plants is affected by the wounding response via an ethylene dependent mechanism

Variability in recombinant IgG yield in transgenic tobacco plants has previously been observed in relation to leaf position, and is interpreted as a function of ageing and the senescence process, leading to increasing protein degradation. Here, similar findings are demonstrated in plants of different ages, expressing IgG but not IgG-HDEL, an antibody form that accumulates within the endoplasmic reticulum. Antibody yields declined following wounding in young transgenic plants expressing IgG but not in those expressing IgG-HDEL. However, in mature IgG plants, the opposite was demonstrated, with significant boosts in yield, while mature IgG-HDEL plants could not be boosted. The lack of response in IgG-HDEL plants suggests that the changes induced by wounding occur post-translationally, and the findings might be explained by wounding responses that differ in plants according to their developmental stages. Plant mechanisms involved in senescence and wounding overlap to a significant degree and compounds such as ethylene, jasmonic acid and salicylic acid are important for mediating downstream effects. Treatment of transgenic plants with ethylene also resulted in a decrease in recombinant IgG yield, which was consistent with the finding that wounded plants could induce lower IgG yields in neighbouring non-wounded plants. Treatment with 1-MCP, an ethylene antagonist, abrogated the IgG yield drop that resulted from wounding, but had no effect on the more gradual IgG yield loss associated with increasing plant age.

Comparison of Growth Responses to Auxin 1-Naphthaleneacetic Acid and the Ethylene Precursor 1-Aminocyclopropane-1-Carboxilic Acid in Maize Seedling Root

Application of 1-naphthaleneacetic acid (NAA) or 1-aminocyclopropane-1-carboxilic acid (ACC) to maize roots growing in hydroponic solution inhibited root elongation, and increased radial growth, but the responses to those treatments differed in degree. Auxin was more effective than ACC as an elongation inhibitor and root swelling promoter. Whereas NAA fully inhibited elongation and maintained swelling over 48 h, ACC inhibited elongation partially (50%) and only promoted swelling for 24 h. It is well-known that auxin, like ACC, promotes ethylene production, but similar levels of ethylene production reached by means of NAA or ACC treatments did not elicit the same response, the response being always stronger to NAA than to ACC. These results suggest that the effect of auxin on root growth is not mediated by ethylene. Elongation and swelling of roots appear to be inversely related: usually a reduction in elongation was accompanied by corresponding swelling. However, these two processes showed different sensitivities to growth regulators. After 24 h treatment with 0.5 μM NAA or 5 μM ACC, root elongation was inhibited by 90% and 53% respectively, but the same treatments promoted swelling by 187% and 140% respectively. Furthermore, 1 μM ACC was shown to promote inhibition of root elongation without affecting swelling. The ethylene antagonist STS (silver thiosulfate) did not affect elongation in control or NAAtreated roots, but increased ethylene production and swelling. These results indicate that longitudinal and radial expansion could be independently controlled.

Synergistic effect of STS and cool storage on postharvest performance of cut spikes of Consolida ajacis cv. violet blue

Cut spikes of Consolida ajacis cv. Violet Blue were used for the study. The ethylene antagonist (STS) was used in combination with cool storage for 72 h at 5°C to assess the synergistic effect of both chemical and temperature treatment on postharvest performance of cut spikes. The spikes were divided into three sets, one set was pretreated with STS (1 h Pulse) prior to wet storage at 5°C for 72 h, while the other set was pretreated after 72 h cool wet storage. The third set of spikes was cool stored (at 5°C) for 72 h but kept unpulsed, which represented control. After 72 h storage, the spikes from all the three sets were transferred to flasks containing distilled water (DW) or 0.2 M sucrose + 100 mg·L−1 8-HQS (SUC + HQS). Pretreatment of spikes with STS before or after wet storage resulted in an improved postharvest performance as compared to the controls. Maximum vase life of about 18 days was shown by spikes pretreated with STS prior to storage and transferred to SUC + HQS as compared to controls which registered a vase life of 10 days in DW and 13 days in SUC + HQS (0.2 M sucrose + 100 mg·L−1 8-HQS). Flower diameter, fresh and dry mass was markedly increased in the samples from spikes transferred to SUC + HQS. Correlation between soluble protein content in sepals and vase life was positive. The results show that soluble protein content in sepals is an important factor in determining the vase life of cut spikes of Consolida ajacis cv. Violet Blue. The study recommends that pulsing the spikes with 0.5 mM STS prior to 72 h wet storage at 5°C and transferring them to holding solution containing SUC + HQS, can be used as a storage/chemical treatment to improve the postharvest performance of this cut flower.

Encapsulation of the Ethylene Inhibitor 1-Methylcyclopropene by Cucurbit[6]uril

1-Methylcyclopropene (1-MCP) is an excellent safe and commercially available ethylene antagonist for the preservation of horticultural products. However 1-MCP has to be stored in absorbents due to its gaseous and unstable characteristics. In this paper cucurbit[6]uril (CB[6]) was used as the absorbent to encapsulate 1-MCP, and the resultant inclusion complex was characterized by IR, powder X-ray diffraction, thermal analysis, and fluorescent spectra. The effects of encapsulation conditions on the formation of inclusion complex were also investigated. The amount of 1-MCP encapsulated by CB[6] was about 4.5% by weight when the initial concentration of 1-MCP, encapsulation temperature, CB[6] concentration, and encapsulation time were set at 75 mL/L, 20 °C, 30 mM, and 8 h, respectively. Furthermore, the release of 1-MCP from the complex can be realized with different solutions such as sodium bicarbonate, benzoic acid, and distilled water. CB[6] can be used as an excellent absorbent for encapsulation of 1-MCP.

Effect of 1-methylcyclopropene (1-MCP) on reducing postharvest decay in tomatoes ( Solanum lycopersicum L.)

1-Methylcyclopropene (1-MCP as SmartFresh™ technology), an ethylene antagonist, was evaluated for affecting postharvest decay caused by Alternaria alternata, Botrytis cinerea, and Fusarium spp. on ‘Quality 23’ and ‘Seminis 35’ tomatoes at green or pink stages. Fruit with natural or artificial infection were subjected to 1-MCP at 0.0 μL L −1, 0.6 μL L −1 for 12 h, and 1.0 μL L −1 for 6 h. After 31–42 d storage, disease incidence and severity of individual diseases in 1-MCP treated fruit was significantly reduced compared with that of the untreated controls, except in one inoculated test for ‘Quality 23’ where severity of Alternaria rot in 1.0 μL L −1 treated fruit were significantly higher than that of the untreated control. Fruit treated with 1-MCP at 1.0 L −1 for 6 h also had significantly higher incidence of Alternaria rot in the inoculated ‘Quality 23’ and in the non-inoculated ‘Seminis 35’ compared with the fruit treated with 1-MCP at 0.6 μL L −1 for 12 h. The results of this study indicate that 1-MCP can reduce postharvest decay within a certain storage period.

Grafting effects on postharvest ripening and quality of 1-methylcyclopropene-treated muskmelon fruit

In addition to managing soil-borne diseases in muskmelon ( Cucumis melo L.) production, grafting with resistant rootstocks may impact fruit quality. The ethylene antagonist 1-methylcyclopropene (1-MCP) has been shown to extend shelf life of fresh muskmelon fruit. Postharvest characteristics of 1-MCP-treated melon fruit as affected by grafting, however, have not been well examined. This study was conducted to explore the influence of grafting with different rootstocks on ripening and quality attributes of 1-MCP-treated muskmelon fruit during postharvest storage. Grafted ‘Athena’ muskmelon with two commercial squash interspecific hybrid rootstocks including ‘Strong Tosa’ and ‘Tetsukabuto’ as well as non-grafted and self-grafted ‘Athena’ were grown in replicated field plots at the University of Florida Plant Science Research and Education Unit (Citra, FL, USA) during April–June 2010. Half-slip fruit from two harvests were treated with 1.0 μL L −1 1-MCP (18 h, 20 °C) and analyzed during storage at 13 °C. For fruit from the 27 May harvest, whole fruit and mesocarp firmness, titratable acidity, soluble solids, and ascorbic acid content were measured, while production of ethylene and CO 2 was determined on fruit from the 29 June harvest. Grafting did not show a significant impact on fruit yield but affected the fruit shelf life significantly. Fruit from non-grafted ‘Athena’ and ‘Athena’ grafted onto ‘Strong Tosa’ demonstrated a shelf life of 31 d for the first harvest and 22 d for the second harvest. Shelf life of fruit from self-grafted ‘Athena’ and ‘Athena’ grafted onto ‘Tetsukabuto’ declined by 6 d and 3 d for the first and second harvest, respectively. Whole fruit firmness decreased by approximately 15.5% on average from 13 to 31 d except day 19 as a result of grafting, but to a lesser extent with ‘Strong Tosa’ rootstock. Mesocarp firmness of grafted melon was reduced by about 30.2% at days 13 and 19 compared to non-grafted ‘Athena’ fruit. In contrast, titratable acidity, soluble solid content, and ascorbic acid concentration were less affected by grafting. All the measurements except for ethylene and CO 2 production declined during storage regardless of the grafting treatment. Compared with ‘Strong Tosa’ rootstock, ‘Tetsukabuto’ resulted in a more rapid ripening under 1-MCP application, as reflected by earlier increase in ethylene production and higher respiratory rate. The study demonstrates that grafting effects on postharvest ripening and quality of ‘Athena’ muskmelon can vary markedly with rootstocks used.

Effect of Ethylene Antagonists (STS and AOA) on Postharvest Senescence of Ranunculus asiaticus L. Flowers

Effect of Ethylene Antagonists (STS and AOA) on Postharvest Senescence of Ranunculus asiaticus L. Flowers

Microarray analysis of ripening-regulated gene expression and its modulation by 1-MCP and hexanal

Hexanal, an inhibitor of phospholipase D, has been successfully applied for the pre- and post-harvest treatment of fruits, vegetables and flowers. Changes in gene expression induced by hexanal and the ethylene antagonist 1-MCP, were analyzed by microarray using TOM2 tomato oligo-array containing approximately 12000 unigenes. Mature green tomato fruits were treated with 1-MCP and hexanal, RNA isolated after 10 days of storage, and labeled cDNA synthesized for microarray analysis. A large variation in gene expression profile was observed in 1-MCP-treated fruits. Genes for ethylene biosynthetic pathway enzymes such as ACC- synthase/oxidase, ethylene receptor and ethylene response factors were heavily down-regulated in 1-MCP-treated fruits. In addition, genes for key enzymes involved in cell wall degradation and carotenoid development pathways were down-regulated. Hexanal treatment significantly down-regulated ACC-synthase, and to a lesser extent, other components of ethylene signal transduction. By contrast to MCP-treated fruits, hexanal-treated fruits gradually ripened and showed higher levels of lycopene and β-carotene. GC-MS analysis of volatiles showed a higher level of major volatile components in hexanal-treated fruits. Similarities in the modulation of gene expression by hexanal and 1-MCP suggest that hexanal, in addition to being a PLD inhibitor, may also act as a weak ethylene inhibitor.

COMPARATIVE TRANSCRIPTOMIC ANALYSIS OF PLUM FRUIT TREATED WITH 1-MCP

Microarray technology has allowed the large scale transcriptomic analysis of fruit ripening. The µPEACH1.0 microarray containing 4,806 probes corresponding to genes expressed in peach fruit tissues has been used in a heterologous fashion in two studies of plums ripening behavior. Gene expression of different cultivars of plums treated with the ethylene antagonist, 1-methylcyclopropene (1-MCP) and stored for short periods at room temperature or for longer periods of cold storage was examined. In the first study, mature fruit of a suppressed ethylene climacteric cultivar ‘Shiro’ and a cultivar characterized by a typical increase of ethylene production during ripening (‘Santa Rosa’) were harvested and incubated for 24h in air (control) or 1-MCP and allowed to ripen at room temperature. Different levels of transcripts of genes implicated in cell wall metabolism, hormone (ethylene and auxin) regulation, stress and defense, and in the transcription/translation machinery, as well as others involved with ripening were identified. In the second study, the effects of 1-MCP on gene expression in relation to the development of chilling injury (CI) in the climacteric cultivars ‘Ruby Red’ (RR) and ‘October Sun’ (OS) and ‘Zee Lady’ peaches (ZP) were analyzed. The fruit were treated for 24h at room temperature with 1-MCP prior to storage at 0°C. For RR, there was no significant effect of 1-MCP on the level of CI symptoms, while 1-MCP significantly reduced CI symptoms in OS fruit and an increase of CI in treated ZP fruit. Microarray analysis showed that immediately following treatment, 186, 134 and 56 genes were differentially expressed between the control and 1-MCP-treated fruit of these cultivars, respectively: after 4 weeks cold storage, 311, 52 and 224 genes for RR, OS and ZP, respectively, were differentially expressed between control and treated fruit. Thus, for OS, the number of differentially expressed genes reduced during storage while the number increased in RR and ZP. Comparisons of the data suggest that the transcript profile is altered by 1-MCP more in plums than peaches. These studies, carried out within an international collaborative network, will increase our understanding of the regulation of pathways involved in plum fruit ripening and in metabolic processes related to storage and shelf life.