Ethylene Receptor Research Articles

Silver ions increase plasma membrane permeability through modulation of intracellular calcium levels in tobacco BY-2 cells.

Silver ions increase plasma membrane permeability for water and small organic compounds through their stimulatory effect on plasma membrane calcium channels, with subsequent modulation of intracellular calcium levels and ion homeostasis. The action of silver ions at the plant plasma membrane is largely connected with the inhibition of ethylene signalling thanks to the ability of silver ion to replace the copper cofactor in the ethylene receptor. A link coupling the action of silver ions and cellular auxin efflux has been suggested earlier by their possible direct interaction with auxin efflux carriers or by influencing plasma membrane permeability. Using tobacco BY-2 cells, we demonstrate here that besides adramatic increase of efflux of synthetic auxins 2,4-dichlorophenoxyacetic acid (2,4-D) and 1-naphthalene acetic acid (NAA), treatment with AgNO3 resulted in enhanced efflux of the cytokinin trans-zeatin (tZ) as well as the auxin structural analogues tryptophan (Trp) and benzoic acid (BA). The application of AgNO3 was accompanied by gradual water loss and plasmolysis. The observed effects were dependent on the availability of extracellular calcium ions (Ca2+) as shown by comparison of transport assays in Ca2+-rich and Ca2+-free buffers and upon treatment with inhibitors of plasma membrane Ca2+-permeable channels Al3+ and ruthenium red, both abolishing the effect of AgNO3. Confocal microscopy of Ca2+-sensitive fluorescence indicator Fluo-4FF, acetoxymethyl (AM) ester suggested that the extracellular Ca2+ availability is necessary to trigger the response to silver ions and that the intracellular Ca2+ pool alone is not sufficient for this effect. Altogether, our data suggest that in plant cells the effects of silver ions originate from the primal modification of the internal calcium levels, possibly by their interaction with Ca2+-permeable channels at the plasma membrane.

H2O2 homeostasis in wild-type and ethylene-insensitive Never ripe tomato in response to salicylic acid treatment in normal photoperiod and in prolonged darkness

Ethylene proved to be an important modulator of salicylic acid (SA) signalling pathway. Since SA may regulate both the production and scavenging of hydrogen peroxide (H2O2), which show light-dependency, the aim of this study was to compare H2O2 metabolism in the leaves of SA-treated wild-type (WT) tomato (Solanum lycopersicum L. cv. Ailsa Craig) and in ethylene receptor Never-ripe (Nr) mutants grown in normal photoperiod or in prolonged darkness. H2O2 accumulation was higher in the WT than in the mutants in normal photoperiod after 1 mM SA treatment, while Nr leaves contained more H2O2 after light deprivation. The expression of certain superoxide dismutase (SOD) genes and activity of the enzyme followed the same tendency as H2O2, which was scavenged by different enzymes in the two genotypes. Catalase (CAT, EC 1.11.1.6) activity was inhibited by SA in WT, while the mutants maintained enhanced enzyme activity in the dark. Thus, in WT, CAT inhibition was the major component of the H2O2 accumulation elicited by 1 mM SA in a normal photoperiod, since the expression and/or activity of ascorbate (APX, EC 1.11.1.11) and guaiacol peroxidases (POD, EC 1.11.1.7) were induced in the leaves. The absence of APX and POD activation in mutant plants suggests that the regulation of these enzymes by SA needs functional ethylene signalling. While the block of ethylene perception in Nr mutants was overwritten in the transcription and activity of certain SOD and CAT isoenzymes during prolonged darkness, the low APX and POD activities led to H2O2 accumulation in these tissues.

Ethylene causes transcriptomic changes in Synechocystis during phototaxis.

Ethylene is well known as a plant hormone, but its role in bacteria is poorly studied. We recently showed that Synechocystis sp. Strain PCC 6803 has a functional receptor for ethylene, ethylene response 1 (Etr1), that is involved in various processes such as phototaxis in response to directional light and biofilm formation. Here, we use RNA sequencing to examine the changes in gene transcripts caused by ethylene under phototaxis conditions. Over 500 gene transcripts across many functional categories, of approximately 3700 protein‐encoding genes, were altered by application of ethylene. In general, ethylene caused both up‐ and downregulation of genes within a functional category. However, the transcript levels of amino acid metabolism genes were mainly upregulated and cell envelope genes were mostly downregulated by ethylene. The changes in cell envelope genes correlate with our prior observation that ethylene affects cell surface properties to alter cell motility. Ethylene caused a twofold or more change in 62 transcripts with the largest category of upregulated genes annotated as transporters and the largest category of downregulated genes annotated as glycosyltransferases which sometimes are involved in changing the composition of sugars on the cell surface. Consistent with changes in cell envelope, glycosyltransferase, and transporter gene transcripts, application of ethylene altered the levels of specific sugar moieties on the surface of cells. Light signaling from Etr1 involves two proteins (Slr1213 and Slr1214) and a small, noncoding RNA, carbon stress‐induced RNA1 (csiR1). Application of ethylene caused a rapid, but transient, decrease in the transcript levels of etr1, slr1213, and slr1214 and a rapid and prolonged decrease in csiR1 transcript. Deletion of Slr1214 caused a large increase in csiR1 transcript levels and ethylene lowered csiR1 transcript. These data combined with prior reports indicate that ethylene functions as a signal to affect a variety of processes altering the physiology of Synechocystis cells.

Recognition motif and mechanism of ripening inhibitory peptides in plant hormone receptor ETR1

Synthetic peptides derived from ethylene-insensitive protein 2 (EIN2), a central regulator of ethylene signalling, were recently shown to delay fruit ripening by interrupting protein–protein interactions in the ethylene signalling pathway. Here, we show that the inhibitory peptide NOP-1 binds to the GAF domain of ETR1 – the prototype of the plant ethylene receptor family. Site-directed mutagenesis and computational studies reveal the peptide interaction site and a plausible molecular mechanism for the ripening inhibition.

Inhibition of tomato fruit ripening by 1-MCP, wortmannin and hexanal is associated with a decrease in transcript levels of phospholipase D and other ripening related genes

Membrane deterioration is an inherent aspect of the advancement in senescence and loss in fruit quality during storage. Postharvest technologies used for extending shelf life and quality are targeted to reduce membrane damage through downregulating or blocking ethylene action. In this study, mature green tomato fruit were treated with inhibitors of ethylene receptor (ETR), phosphatidylinositol 3-kinase (PI3K) and phospholipase D (PLD), all recognized to be targets of regulation of fruit ripening. The inhibitors used included 1-methylcyclopropene (1-MCP, an ethylene receptor blocker), wortmannin (an inhibitor of PI3K), and hexanal (a PLD inhibitor). Fruit were treated at optimal levels of the inhibitors and were stored at 21 °C for 10 days. Color development was strongly delayed in wortmannin treated tomatoes just as in 1-MCP treated fruit; while, changes in respiration, firmness and ethylene evolution were very similar to that of control fruit. Hexanal delayed the initiation of these changes; while 1-MCP and wortmannin blocked the ripening process. Changes in expression levels of key genes involved in ethylene signalling, phosphoinositide metabolism, and lycopene synthesis that occurred in response to inhibitors, suggested potential roles for PI3K and PLD in ethylene signalling. Furthermore, fruit treated with all the three inhibitors showed a marked reduction in PLD transcript levels; suggesting that, regulation of PLD gene expression is a common critical regulatory point that regulates ripening. Lowered PLD levels may reduce membrane lipid catabolism and the generation of phosphatidic acid (PA), an intermediate in ethylene signalling regulation through downstream components.

Role of ethylene and related gene expression in the interaction between strawberry plants and the plant growth-promoting bacterium Azospirillum brasilense.

Induced systemic resistance (ISR) is one of the indirect mechanisms of growth promotion exerted by plant growth-promoting bacteria, and can be mediated by ethylene (ET). We assessed ET production and the expression of related genes in the Azospirillum-strawberry plant interaction. Ethylene production was evaluated by gas chromatography in plants inoculated or not with A.brasilense REC3. Also, plants were treated with AgNO3 , an inhibitor of ET biosynthesis; with 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ET biosynthesis; and with indole acetic acid (IAA). Plant dry biomass and the growth index were determined to assess the growth-promoting effect of A.brasilense REC3 in strawberry plants. Quantitative real time PCR (qRT-PCR) was performed to analyse relative expression of the genes Faetr1, Faers1 and Faein4, which encode ET receptors; Factr1 and Faein2, involved in the ET signalling pathway; Faacs1 encoding ACC synthase; Faaco1 encoding ACC oxidase; and Faaux1 and Faami1 for IAA synthesis enzymes. Results showed that ET acts as a rapid and transient signal in the first 12h post-treatment. A.brasilense REC3-inoculated plants had a significantly higher growth index compared to control plants. Modulation of the genes Faetr1, Faers1, Faein4, Factr1, Faein2 and Faaco1 indicated activation of ET synthesis and signalling pathways. The up-regulation of Faaux1 and Faami1 involved in IAA synthesis suggested that inoculation with A.brasilense REC3 induces production of this auxin, modulating ET signalling. Ethylene production and up-regulation of genes associated with ET signalling in strawberry plants inoculated with A.brasilense REC3 support the priming activation characteristic of ISR. This type of resistance and the activation of systemic acquired resistance previously observed in this interaction indicate that both are present in strawberry plants, could act synergistically and increase protection against pathogens.

The effect of 1-methylcyclopropene (1-MCP) on expression of ethylene receptor genes in durian pulp during ripening

Rapid fruit ripening is a significant problem that limits the shelf life of durian, with ethylene having a major impact on the regulation of this event. Durian treated with ethephon ripened 3 d after treatment with increased pulp total soluble solids, ethylene production of the whole fruit and decreased pulp firmness compared to the control fruit. 1-MCP treatment delayed ripening by up to 9 d with inhibited accumulation of total soluble solids, color change, softening and ethylene production. Genes related to ethylene perception (DzETR1 and DzETR2) and the signaling pathway (DzCTR1, DzEIL1 and DzEIL2) in the pulp were investigated during this process, using qPCR to quantify changes in gene transcription. All candidate genes were significantly up-regulated in ripening durian pulp. Ethephon treatment increased the expression of DzETR1 and DzETR2 genes, while expression of DzCTR1, DzEIL1 and DzEIL2 were slightly affected. 1-MCP treatment significantly inhibited the expression of the DzETR2 and DzEIL1 genes. The promoters of DzETR2 genes were isolated and their activation by fruit transcription factors studied using transient expression in tobacco leaves. It was found that members of the kiwifruit and apple EIL1, EIL2 and EIL3 genes strongly activated the DzETR2 promoter. These results suggest that ethylene-induced ripening of durian is via the regulation of DzETR2 by EIL transcription factors.

Programmed cell death in wheat (Triticum aestivum L.) endosperm cells is affected by drought stress.

Drought frequently occurs during wheat (Triticum aestivum L.) grain filling. The objectives of this study were (i) to investigate the effect of post-anthesis drought on programmed cell death (PCD) in wheat endosperm cells and (ii) to examine the role of ethylene (ETH) receptors and abscisic acid (ABA) in regulating wheat endosperm PCD. Two winter wheat cultivars ('Xindong 18' and 'Xindong 22') were used in this study. Grain samples were collected from normal and drought stressed plants at 5-day intervals between 5 and 35days post-anthesis. The samples were then compared with respect to cell viability, nuclear morphometry, cell ultrastructure, DNA integrity, nucleic acid content, and nuclease activity. Analysis was also conducted about gene transcripts related to PCD, ETH receptors, and ABA biosynthesis and degradation. Drought stress reduced cell viability, accelerated nuclear deformation, and increased mitochondrial dissolution. The activity of nucleic acid hydrolase was greater, and the nucleic acid concentrations were less in the drought treatments than in the control. As a result, the peak in DNA fragmentation occurred earlier in the drought treatment. Drought stress significantly increased the expression of four genes related to ABA (nced1, nced2, ao1, ao2). In contrast, drought significantly reduced the expression of four genes related to ETH receptors (ers1, ers2 etr1, etr2) and one gene related to PCD (dad1). In summary, the results indicated that drought stress caused PCD to occur earlier in the endosperm of winter wheat.

Correction: Hydrogen sulfide alleviates postharvest ripening and senescence of banana by antagonizing the effect of ethylene.

[This corrects the article DOI: 10.1371/journal.pone.0180113.].

Physiological Responses of Banana Fruit to Two Structural Analogues of 1-MCP as Ethylene Action Inhibitors

Ethylene induced actions during fruit ripening have been found to be inhibited by 1-methylcyclopropene (1-MCP) and possibly its analogues by competing for the sites of binding on the ethylene receptor. The purpose of this study was to evaluate the effect of treatment with 1-PentCP or 1-OCP, two structural analogues of 1-MCP, on inhibiting ethylene action in banana (Musa sapientum L.) fruit. The banana fruit after being fumigated for 20 h at 20±2°C with 0 (control), 0.4, 0.8 or 1.2 μl l-1 of 1-MCP, 1-PentCP or 1-OCP were stored in air environment at 20±2°C for ripening assessment. Ethylene production, color change, firmness, ACS activity, ACO activity and ACC content of the fruits were measured every 5 days during storage. The results of our study showed that these two structural analogues, just as 1-MCP, exerted their effect in a concentration-depended manner. 1-OCP was found to inhibit ethylene-induced ripening of banana fruit at a low concentration relatively. Treatment for 20 h with 0.8 μl l-1 1-OCP or 1.2 μl l-1 1-PentCP all delayed ethylene climacteric peak of banana fruit by 10 days as compared with the untreated group, after which the banana fruit resumed normal ripening. Softening and color change of banana fruit was restrained by the two structural analogues. Increasing the concentration of 1-PentCP to 1.2 μl l-1 caused a marked delay in softening and color change, but increasing the concentration of 1-OCP to 1.2 μl l-1 or higher did not result in a further delay in softening and color change. The results indicated that treatment with 0.8 μl l-1 1-OCP is sufficient to exert maximal delay of banana fruit ripening. Treatment with the most effective concentration of 1-OCP or 1-PentCP delayed ACC content, ACS activity and ACO activity of banana fruit as compared with the untreated group, but less effective than 1.2 μl l-1 1-MCP. It is suggested that 1-OCP was found to be a more potent inhibitor of banana fruit ripening than 1-PentCP, but less potent than the mother compound 1-MCP. The two structural analogues are beneficial to fruit storage and enhance the fruit resistance to decay that can be promised to be applied in agricultural practice.

Cross-regulation of Arabidopsis root growth by plant hormones auxins and ethylene

We investigated the cross-talk between auxin (IAA) and ethylene in the control of root growth of Arabidopsis plants (Arabidopsis thaliana). The root growth of ethylene insensitive etr1-1 and auxin insensitive tir1 mutants under the effect of IAA and 1-methylcyclopropene (1-MCP, inhibitor of ethylene perception) was compared, respectively, with that of the wild type ecotype Columbia (Col-0). Roots of Col-0 were shorter than those of the etr1-1 mutant. The addition of IAA (5.7 × 10–6 М) to the growth medium led to 20 % root shortening in Col-0 plants, but not in etr1-1 mutants. Thus, the capacity of plants for ethylene perception contributes to the control of root length and its sensitivity to IAA. Roots of etr1-1 were less heavy than in Col-0, indicating that ethylene maintains root mass accumulation. Treatment with IAA caused a decrease in root mass of both genotypes (resulting in a 25 and 10 % decline in the root mass of Col-0 and etr1-1 as compared to the corresponding control), suggesting that IAA may influence root biomass accumulation independently of ethylene. However, sensitivity to ethylene increases plant responsiveness to IAA. Mutation in the auxin receptor decreased the sensitivity of roots to inactivation of ethylene receptors: treatment with 1-MCP resulted in a 40 % decline in the root mass of Col-0 and only a 10 % decrease in tir1. The decrement in sensitivity to auxins in the tir1 mutant decreased the responsiveness of root biomass to 1-MCP-treatment. These data suggest an additive action of ethylene and auxins on accumulation of root biomass.

Identification of Transcriptional and Receptor Networks That Control Root Responses to Ethylene

Transcriptomic analyses with high temporal resolution provide substantial new insight into hormonal response networks. This study identified the kinetics of genome-wide transcript abundance changes in response to elevated levels of the plant hormone ethylene in roots from light-grown Arabidopsis (Arabidopsis thaliana) seedlings, which were overlaid on time-matched developmental changes. Functional annotation of clusters of transcripts with similar temporal patterns revealed rapidly induced clusters with known ethylene function and more slowly regulated clusters with novel predicted functions linked to root development. In contrast to studies with dark-grown seedlings, where the canonical ethylene response transcription factor, EIN3, is central to ethylene-mediated development, the roots of ein3 and eil1 single and double mutants still respond to ethylene in light-grown seedlings. Additionally, a subset of these clusters of ethylene-responsive transcripts were enriched in targets of EIN3 and ERFs. These results are consistent with EIN3-independent developmental and transcriptional changes in light-grown roots. Examination of single and multiple gain-of-function and loss-of-function receptor mutants revealed that, of the five ethylene receptors, ETR1 controls lateral root and root hair initiation and elongation and the synthesis of other receptors. These results provide new insight into the transcriptional and developmental responses to ethylene in light-grown seedlings.

Ethylene production and constitutive expression of ethylene receptors and ethylene signal transduction during grain filling in apical and basal spikelets of compact-and lax-panicle rice (Oryza sativa) cultivars

Ethylene production and constitutive expression of ethylene receptors and ethylene signal transduction during grain filling in apical and basal spikelets of compact-and lax-panicle rice (Oryza sativa) cultivars

Thap Maeo bananas: Fast ripening and full ethylene perception at low doses

Brazil is a major producer and consumer of various banana types. Thap Maeo is a promising cultivar for the market due to its resistance to Black and Yellow Sigatoka disease. However, a lack of information and postharvest technologies concerning Thap Maeo physiology seems to be a significant problem limiting its expansion in the market. Thus, this study aims to establish Thap Maeo fruit's physical, biochemical, and physiological aspects, defining the best ethylene dosage for treatment considering fruit ripening parameters. Bananas were harvested and monitored during both natural and ethylene-induced ripening processes. Assessments of pulp firmness, peel color and endogenous ethylene production showed different profiles between ethylene-treated and non-treated fruits, whereas the ethylene responses concerning the carbohydrates and hormones profiles, as well as the ethylene receptors expression, were observed in all ethylene-treated fruits, even applying low concentrations of the hormone. It thus indicated the high ethylene-sensitivity of Thap Maeo cultivar. Such postharvest behaviors reverberate in lower ethylene requirements for treatment, which was established at 10μLL−1. Ethylene-inducible changes in fruit volatile compounds throughout ripening are also discussed.

Arabidopsis CPR5 regulates ethylene signaling via molecular association with the ETR1 receptor.

The plant hormone ethylene plays various functions in plant growth, development and response to environmental stress. Ethylene is perceived by membrane-bound ethylene receptors, and among the homologous receptors in Arabidopsis, the ETR1 ethylene receptor plays a major role. The present study provides evidence demonstrating that Arabidopsis CPR5 functions as a novel ETR1 receptor-interacting protein in regulating ethylene response and signaling. Yeast split ubiquitin assays and bi-fluorescence complementation studies in plant cells indicated that CPR5 directly interacts with the ETR1 receptor. Genetic analyses indicated that mutant alleles of cpr5 can suppress ethylene insensitivity in both etr1-1 and etr1-2, but not in other dominant ethylene receptor mutants. Overexpression of Arabidopsis CPR5 either in transgenic Arabidopsis plants, or ectopically in tobacco, significantly enhanced ethylene sensitivity. These findings indicate that CPR5 plays a critical role in regulating ethylene signaling. CPR5 is localized to endomembrane structures and the nucleus, and is involved in various regulatory pathways, including pathogenesis, leaf senescence, and spontaneous cell death. This study provides evidence for a novel regulatory function played by CPR5 in the ethylene receptor signaling pathway in Arabidopsis.

Abscisic Acid-Induced Reactive Oxygen Species Are Modulated by Flavonols to Control Stomata Aperture.

Abscisic acid (ABA) increases reactive oxygen species (ROS) in guard cells to close Arabidopsis (Arabidopsis thaliana) stomata. In tomato (Solanum lycopersicum), we find that ABA-increased ROS is followed by stomatal closure and that both responses are blocked by inhibitors of ROS-producing respiratory burst oxidase enzymes. ABA-induced ROS sensor fluorescence accumulates in the nucleus, chloroplasts, and endomembranes. The accumulation of flavonol antioxidants in guard cells, but not surrounding pavement cells, was visualized by confocal microscopy using a flavonol-specific fluorescent dye. Decreased flavonols in guard cells in the anthocyanin reduced (are) mutant and elevated levels in the anthocyanin without (aw) mutant were quantified by confocal microscopy and in leaf extracts by mass spectrometry. Consistent with flavonols acting as antioxidants, higher levels of ROS were detected in guard cells of the tomato are mutant and lower levels were detected in aw both at homeostasis and after treatment with ABA. These results demonstrate the inverse relationship between flavonols and ROS. Guard cells of are show greater ABA-induced closure than the wild type, reduced light-dependent guard cell opening, and reduced water loss, with aw having opposite responses. Ethylene treatment of wild-type tomato plants increased flavonol accumulation in guard cells; however, no flavonol increases were observed in Neverripe (Nr), an ethylene receptor mutant. Consistent with lower levels of ROS due to elevated flavonols, ethylene treatments decreased ABA-induced stomatal closure in the wild type, but not Nr, with ethylene responses attenuated in the are mutant. Together, these results are consistent with flavonols dampening the ABA-dependent ROS burst that drives stomatal closure and facilitating stomatal opening to modulate leaf gas exchange.

Potential vase life of cut roses: Seasonal variation and relationships with growth conditions, phenotypes, and gene expressions

In this work, we identified the interrelationships between gene expression levels, environmental factors, phenotypic characteristics, and vase life of cut rose ‘Lovely Lydia’ between seasons and across years. We also determined the contribution of each factor to potential vase life (PVL) of cut roses. The vase life of the cut flowers was longest in spring (12.2 d), followed by summer (11.3 d), autumn (10.0 d), and winter (9.2 d). The environmental conditions in winter were characterized by high relative humidity (RH) and low vapor pressure deficit, and cut flowers grown under these conditions had less-functional stomata and consequently excessive water loss after harvest, resulting in shortened vase life. Leaf brix was not significantly correlated with PVL, but it was strongly correlated with flower diameter, indicating that congenital sucrose may be more important for providing the substances required for flower opening than for determining the longevity of cut roses. Correlation analysis revealed that initial transcript levels of the ethylene receptor RhETR4 and the signaling component RhEIN3-2 are very important factors in determining PVL of cut roses, as are preharvest RH conditions, stomatal function, and transpiration. The transcript levels of these genes were significantly modified by growth environment, including high RH and low temperature. Importantly, we show that RH conditions during cultivation not only determine stomatal characteristics but also modify the initial transcript levels of the ethylene responsive genes, thereby modifying the PVL. Understanding the interrelationships of genetic variation with other factors in the modulation of PVL will greatly help to improve growth environments and postharvest treatments across seasons as well as to develop techniques for guaranteeing the longevity of cut flowers.

Novel Protein-Protein Inhibitor Based Approach to Control Plant Ethylene Responses: Synthetic Peptides for Ripening Control

Ethylene signaling is decisive for many plant developmental processes. Among these, control of senescence, abscission and fruit ripening are of fundamental relevance for global agriculture. Consequently, detailed knowledge of the signaling network along with the molecular processes of signal perception and transfer are expected to have high impact on future food production and agriculture. Recent advances in ethylene research have demonstrated that signaling of the plant hormone critically depends on the interaction of the ethylene receptor family with the NRAMP-like membrane protein ETHYLENE INSENSITIVE 2 (EIN2) at the ER membrane, phosphorylation-dependent proteolytic processing of ER-localized EIN2 and subsequent translocation of the cleaved EIN2 C-terminal polypeptide (EIN2-CEND) to the nucleus. EIN2 nuclear transport, but also interaction with the receptors sensing the ethylene signal, both, depend on a nuclear localization signal (NLS) located at the EIN2 C-terminus. Loss of the tight interaction between receptors and EIN2 affects ethylene signaling and impairs plant ethylene responses. Synthetic peptides derived from the NLS sequence interfere with the EIN2–receptor interaction and have utility in controlling plant ethylene responses such as ripening. Here, we report that a synthetic peptide (NOP-1) corresponding to the NLS motif of Arabidopsis EIN2 (aa 1262–1269) efficiently binds to tomato ethylene receptors LeETR4 and NR and delays ripening in the post-harvest phase when applied to the surface of sampled green fruits pre-harvest. In particular, degradation of chlorophylls was delayed by several days, as monitored by optical sensors and confirmed by analytical methods. Similarly, accumulation of β-carotene and lycopene in the fruit pulp after NOP-1 application was delayed, without having impact on the total pigment concentration in the completely ripe fruits. Likewise, the peptide had no negative effects on fruit quality. Our molecular and phenotypic studies reveal that peptide biologicals could contribute to the development of a novel family of ripening inhibitors and innovative ripening control in climacteric fruit.

Heat stress differentially modifies ethylene biosynthesis and signaling in pea floral and fruit tissues.

Ethylene biosynthesis is regulated in reproductive tissues in response to heat stress in a manner to optimize resource allocation to pollinated fruits with developing seeds. High temperatures during reproductive development are particularly detrimental to crop fruit/seed production. Ethylene plays vital roles in plant development and abiotic stress responses; however, little is known about ethylene's role in reproductive tissues during development under heat stress. We assessed ethylene biosynthesis and signaling regulation within the reproductive and associated tissues of pea during the developmental phase that sets the stage for fruit-set and seed development under normal and heat-stress conditions. The transcript abundance profiles of PsACS [encode enzymes that convert S-adenosyl-L-methionine to 1-aminocyclopropane-1-carboxylic acid (ACC)] and PsACO (encode enzymes that convert ACC to ethylene), and ethylene evolution were developmentally, environmentally, and tissue-specifically regulated in the floral/fruit/pedicel tissues of pea. Higher transcript abundance of PsACS and PsACO in the ovaries, and PsACO in the pedicels was correlated with higher ethylene evolution and ovary senescence and pedicel abscission in fruits that were not pollinated under control temperature conditions. Under heat-stress conditions, up-regulation of ethylene biosynthesis gene expression in pre-pollinated ovaries was also associated with higher ethylene evolution and lower retention of these fruits. Following successful pollination and ovule fertilization, heat-stress modified PsACS and PsACO transcript profiles in a manner that suppressed ovary ethylene evolution. The normal ethylene burst in the stigma/style and petals following pollination was also suppressed by heat-stress. Transcript abundance profiles of ethylene receptor and signaling-related genes acted as qualitative markers of tissue ethylene signaling events. These data support the hypothesis that ethylene biosynthesis is regulated in reproductive tissues in response to heat stress to modulate resource allocation dynamics.

Role of abscisic acid and ethylene in the control of water transport-driving forces in germinating petunia male gametophyte

Data on ABA involvement in osmoregulation of in vitro germinating petunia (Petunia hybrida L.) male gametophyte were obtained. Two potential targets of ABA action in a pollen tube (PT) are identified. These are represented by (1) plasma membrane (PM) H+-ATPase, electrogenic proton pump participating in PM polarization, and (2) Ca-dependent K+-channels localized in the same membrane. It was established that a stimulatory effect of ABA on electrogenic activity of H+-ATPase is mediated by the increase in free Ca2+ level in the cytosol of a PT and reactive oxygen species (ROS) generation. Based on the results obtained on the role of K+ ions in the hormonal control of water transport-driving forces in a PT, the hypothesis suggesting that ABA stimulated pollen grains (PGs) germinating and PT growth by activating K+-channels was put forward. The revealed ABA-induced shift in cytoplasmic pH (pHc) is suggested to be involved in a cascade of the events of the progamic phase of fertilization, including pH-dependent K+-channels functioning. It was established that ABA abolishes the inhibitory effects of ethylene receptors blocker, 1-methylcyclopropene (1-MCP), and blockers of ACC and ABA synthesis (aminooxyacetic acid, AOA, and fluridone, respectively) on PT germination and growth, whereas ethrel blocks the inhibitory effect of fluridone on PT growth. In stigmas pretreated with ABA and AOA before pollination, this phytohormone was found to suppress inhibitory effect of AOA on ACC synthesis in the pollen-pistil system. All these findings, taken together, led us to the conclusion that ABA is involved in petunia male gametophyte osmoregulation interacting with ethylene at the level of ACC synthesis in the progamic phase of fertilization.