Stimulates Ethylene Biosynthesis Research Articles

Physiological and metabolic changes in response to Boron levels are mediated by ethylene affecting tomato fruit yield

Boron (B) is an essential nutrient for the plant, and its stress (both deficiency and toxicity) are major problems that affect crop production. Ethylene metabolism (both signaling and production) is important to plants’ differently responding to nutrient availability. To better understand the connections between B and ethylene, here we investigate the function of ethylene in the responses of tomato (Solanum lycopersicum) plants to B stress (deficiency, 0 μM and toxicity, 640 μM), using ethylene related mutants, namely nonripening (nor), ripening-inhibitor (rin), never ripe (Nr), and epinastic (Epi). Our results show that B stress does not necessarily inhibit plant growth, but both B stress and ethylene signaling severely affected physiological parameters, such as photosynthesis, stomatal conductance, and chlorophyll a fluorescence. Under B toxicity, visible symptoms of toxicity appeared in the roots and margins of the older leaves through necrosis, caused by the accumulation of B which stimulated ethylene biosynthesis in the shoots. Both nor and rin (ethylene signaling) mutants presented similar responses, being these genotypes more sensitive and displaying several morphophysiological alterations, including fruit productivity reductions, in response to the B toxicity conditions. Therefore, our results suggest that physiological and metabolic changes in response to B fluctuations are likely mediated by ethylene signaling.

The Role of Auxin-Ethylene Crosstalk in Orchestrating Primary Root Elongation in Sugar Beet.

It is well-established in Arabidopsis and other species that ethylene inhibits root elongation through the action of auxin. In sugar beet (Beta vulgaris L.) ethylene promotes root elongation in a concentration dependent manner. However, the crosstalk between ethylene and auxin remains unknown during sugar beet seedling development. Our experiments have shown that exogenously applied auxin (indole-3-acetic acid; IAA) also stimulates root elongation. We also show that auxin promotes ethylene biosynthesis leading to longer roots. We have further demonstrated that the auxin treatment stimulates ethylene production by redirecting the pool of available 1-aminocyclopropane-1-carboxylic acid (ACC) toward ethylene instead of malonyl-ACC (MACC) resulting in a prolonged period of high rates of ethylene production and subsequently a longer root. On the other hand we have also shown that endogenous IAA levels were not affected by an ACC treatment during germination. All together our findings suggest that the general model for auxin-ethylene crosstalk during early root development, where ethylene controls auxin biosynthesis and transport, does not occur in sugar beet. On the contrary, we have shown that the opposite, where auxin stimulates ethylene biosynthesis, is true for sugar beet root development.

Euphorbia milii-Endophytic Bacteria Interactions Affect Hormonal Levels of the Native Host Differently Under Various Airborne Pollutants.

This study was conducted to assess the effect of plant-native endophytic bacteria interactions on indole-3-acetic acid (IAA), ethylene levels, and hormonal balance of Euphorbia milii under different airborne pollutants. IAA levels and airborne formaldehyde removal by E. milii enhanced when inoculated with endophytic isolates. However, one isolate, designated as root endophyte 4, with the highest levels of IAA production individually, declined gaseous formaldehyde removal of plant, since it disturbed hormonal balance of E. milii, leading to IAA levels higher than physiological concentrations, which stimulated ethylene biosynthesis and stomatal closure under light conditions. However, plant-root endophyte 4 interactions favored airborne benzene removal, since benzene was more phytotoxic and the plant needed more IAA to protect against benzene phytotoxicity. As trimethylamine (TMA) was not toxic, it did not affect plant-endophyte interactions. Therefore, IAA levels of root endophyte 4-inoculated E. milii was not significantly different from a noninoculated one. Under mixed-pollutant stress (formaldehyde, benzene, TMA), root endophyte 4-inoculated E. milii removed benzene at the lowest rate, since benzene was the most phytotoxic pollutant with the greatest molecular mass. However, TMA (with greater molecular mass) was removed faster than formaldehyde due to higher phytotoxicity of formaldehyde. Plant-endophyte interactions were affected differently under various airborne pollutants.

Effect of endophytic Bacillus cereus ERBP inoculation into non-native host: Potentials and challenges for airborne formaldehyde removal

Phytoremediation could be a cost-effective, environmentally friendly approach for the treatment of indoor air. However, some drawbacks still dispute the expediency of phytotechnology. Our objectives were to investigate the competency of plant growth-promoting (PGP) endophytic Bacillus cereus ERBP (endophyte root blue pea), isolated from the root of Clitoria ternatea, to colonize and stabilize within Zamioculcas zamiifolia and Euphorbia milii as non-native hosts without causing any disease or stress symptoms. Moreover, the impact of B. cereus ERBP on the natural shoot endophytic community and for the airborne formaldehyde removal capability of non-native hosts was assessed. Non-native Z. zamiifolia was effectively inoculated with B. cereus ERBP through soil as the most efficient method of endophyte inoculation. Denaturing gradient gel electrophoresis profiling of the shoot endophytic community verified the colonization and stability of B. cereus ERBP within its non-native host during a 20-d fumigation period without interfering with the natural shoot endophytic diversity of Z. zamiifolia. B. cereus ERBP conferred full protection to its non-native host against formaldehyde phytotoxicity and enhanced airborne formaldehyde removal of Z. zamiifolia whereas non-inoculated plants suffered from formaldehyde phytotoxicity because their natural shoot endophytic community was detrimentally affected by formaldehyde. In contrast, B. cereus ERBP inoculation into non-native E. milii deteriorated airborne formaldehyde removal of the non-native host (compared to a non-inoculated one) as B. cereus ERBP interfered with natural shoot endophytic community of E. milii, which caused stress symptoms and stimulated ethylene biosynthesis. Non-native host inoculation with PGP B. cereus ERBP could bear potentials and challenges for airborne formaldehyde removal.

Ethylene signalling is mediating the early cadmium-induced oxidative challenge in Arabidopsis thaliana

Cadmium (Cd) induces the generation of reactive oxygen species (ROS) and stimulates ethylene biosynthesis. The phytohormone ethylene is a regulator of many developmental and physiological plant processes as well as stress responses. Previous research indicated various links between ethylene signalling and oxidative stress. Our results support a correlation between the Cd-induced oxidative challenge and ethylene signalling in Arabidopsis thaliana leaves. The effects of 24 or 72h exposure to 5μM Cd on plant growth and several oxidative stress-related parameters were compared between wild-type (WT) and ethylene insensitive mutants (etr1-1, ein2-1, ein3-1). Cadmium-induced responses observed in WT plants were mainly affected in etr1-1 and ein2-1 mutants, of which the growth was less inhibited by Cd exposure as compared to WT and ein3-1 mutants. Both etr1-1 and ein2-1 showed a delayed response in the glutathione (GSH) metabolism, including GSH levels and transcript levels of GSH synthesising and recycling enzymes. Furthermore, the expression of different oxidative stress marker genes was significantly lower in Cd-exposed ein2-1 mutants, evidencing that ethylene signalling is involved in early responses to Cd stress. A model for the cross-talk between ethylene signalling and oxidative stress is proposed.

Role of abscisic acid and ethylene in sweet cherry fruit maturation: molecular aspects

To investigate the role of abscisic acid (ABA) and ethylene in the maturation of sweet cherry fruit, cloning was carried out on one cDNA (PacNCED1) encoding 9-cis-epoxycarotenoid dioxygenase (NCED)—a key enzyme in ABA biosynthesis—and on one cDNA (PacACO1) encoding 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase—an enzyme involved in ethylene biosynthesis. A BLAST homology search revealed that the sequences of DNA and amino acids in both PacNCED1 and PacACO1 showed a high degree of homology to comparable molecules of other plant species. The expression of PacNCED1 increased at the beginning of maturation and peaked 4 days before harvest, which was consistent with ABA accumulation during cherry ripening. Application of exogenous ABA increased the ABA content, inducing the expression of PacNCED1, and promoted ripening via enhancing colour formation and sugar accumulation. The expression of PacACO1 was not observed, and ethylene production was below detection levels, during the entire process of fruit development. The application of ABA or ethephon induced the expression of PacACO1 and stimulated ethylene biosynthesis. The results suggested that ABA—regulated by PacNCED1—may be the key factor in the control of sweet cherry fruit ripening. Exogenous ABA stimulated ethylene production via regulation of PacACO1 expression, which indicated that cherry fruits may have the potential to synthesize ethylene.

Elevated H2O2 production via overexpression of a chloroplastic Cu/ZnSOD gene of lily (Lilium oriental hybrid ‘Marco Polo’) triggers ethylene synthesis in transgenic potato

Transgenic potato plants (SS2 and SS4) that overexpressed a chloroplastic copper/zinc superoxide dismutase lily gene were utilized as an H(2)O(2)-inducible system in order to study the role of H(2)O(2) as a signaling molecule in the biosynthesis of ethylene. SS2 and SS4 plants grown in vitro under sealed microenvironment (SME) conditions displayed anomalous phenotypes including reduction of stem elongation, radial stem growth, and promotion of root hair formation in the generated root, which were similar to ethylene-induced responses. In addition, SS4 plants showed severe vitrification in developing leaves and elevated ethylene production under SME conditions. After the ethylene action inhibitor AgNO(3), 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO) inhibitor CoCl(2), and ACC synthase inhibitor L -aminoethoxyvinylglycine were added to the growth media, the anomalous phenotypes in SS4 plants reverted to their normal phenotype with a concurrent decrease in ethylene production. Northern blot analysis showed that ACO transcripts in SS4 plants were constantly at high levels under normal and SME conditions, indicating that a high level of H(2)O(2) in SS4 plants up-regulates ACO transcripts. Moreover, the direct treatment of H(2)O(2) in potato plants confirmed the elevated expression of the ACO gene. Taken together, these data suggest that the high concentration of H(2)O(2) in transgenic potato plants stimulates ethylene biosynthesis by activating ACO gene expression.

Effects of iron toxicity on osmotic potential, osmolytes and polyamines concentrations in the African rice ( Oryza glaberrima Steud.)

The African rice species Oryza glaberrima is well adapted to iron toxicity frequently occurring under flooded conditions. Seedlings belonging to two cultivars differing in their level of resistance to iron stress ( TOG 7105: resistant and IRGC 104047: sensitive) were grown in hydroponic culture for 2 weeks and treated with 0, 250 and 500 mg l −1 Fe 2+. Iron concentration in roots was higher in the resistant cv. TOG 7105 than in the sensitive cv. IRGC 104047, while an opposite trend was recorded in laminae, thus suggesting that iron exclusion could be an efficient mechanism of iron resistance. Osmotic potential in laminae decreased to a higher extent in cv. IRGC 104047 than in cv. TOG 7105. Proline and soluble sugars concentrations increased in the iron-sensitive cv. IRGC 104047 only and remained unaffected in the resistant one. Polyamine concentrations were always higher in cv. TOG 7105 than in cv. IRGC 104047, whatever the organ and the duration of treatment. Iron treatment stimulated ethylene biosynthesis to a higher extent in TOG 7105 than in IRGC 104047. These results are discussed in relation to the physiological strategies involved in iron stress resistance in African rice.

Effect of substrate-dependent microbial ethylene production on plant growth

Various compounds have been identified as precursors/substrates for the synthesis of ethylene (C2H4) in soil. This study was designed to compare the efficiency of four substrates, namely L-methionine (L-MET), 2-keto-4-methylthiobutyric acid (KMBA), 1-aminocyclopropane-1-carboxylic acid (ACC), and calcium carbide (CaC2), for ethylene biosynthesis in a sandy clay loam soil by gas chromatography. The classic “triple” response in etiolated pea seedling was employed as a bioassay to demonstrate the effect of substrate-dependent microbial production of ethylene on plant growth. Results revealed that an amendment with L-MET, KMBA, ACC (up to 0.10 g/kg soil) and CaC2 (0.20 g/kg soil) significantly stimulated ethylene biosynthesis in soil. Overall, ACC proved to be the most effective substrate for ethylene production (1434 nmol/kg soil), followed by KMBA, L-MET, and CaC2 in descending order. Results further revealed that ethylene accumulation in soil from these substrates caused a classic “triple” response in etiolated pea seedlings with different degrees of efficacy. A more obvious classic “triple” response was observed at 0.15, 0.10, and 0.20 g/kg soil of L-MET, KMBA/ACC, and CaC2, respectively. Similarly, direct exposure of etiolated pea seedlings to commercial ethylene gas also modified the growth pattern in the same way. A significant direct correlation (r = 0.86 to 0.97) between substrate-derived C2H4 and the classic triple response in etiolated pea seedlings was observed. This study demonstrated that the presence of substrate(s) in soil may lead to increased ethylene concentration in the air of the soil, which may affect plant growth in a desired direction.

Ethylene‐triggered abscisic acid: A principle in plant growth regulation?

The application of auxins to sensitive plant species or their overproduction in transgenic plants stimulates ethylene biosynthesis via induction of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthase. Recent studies with auxin herbicides and indole‐3‐acetic acid (IAA) have revealed that auxin‐stimulated ethylene triggers an increase in the biosynthesis of abscisic acid (ABA), which then functions as a second messenger, leading to growth inhibition and senescence. This raises the question of whether ethylene‐triggered ABA is restricted to the action of auxin herbicides or whether it is a widespread phenomenon in the normal plant growth regulation. Our own results and a reappraisal of the literature indicate that ethylene‐induced ABA may, indeed, play a role in natural physiological phenomena, such as root gravireaction and suppression of lateral bud growth in apical dominance. In addition, it would be worthwhile to investigate whether ethylene‐triggered ABA is involved in other processes which coincide with a strong stimulation of ethylene biosynthesis, such as growth inhibition induced by cytokinins and senescence elicited under stress conditions.

Pepper gene encoding a basic pathogenesis‐related 1 protein is pathogen and ethylene inducible

A new basic pathogenesis‐related (PR)‐1 cDNA (CABPR1) was isolated from a cDNA library of pepper leaves infected with Xanthomonas campestris pv. vesicatoria. The full‐length clone contains an open reading frame of 531 nucleotides encoding 177 amino acid residues with a predicted molecular mass of 20241 and pI of 8.1. The deduced amino acid sequence of CABPR1 has a high level of identity with PR‐1 proteins from tobacco and tomato. Expression of the CABPR1 mRNA was greatly induced in an incompatible interaction of pepper leaves with X. campestris pv. vesicatoria. Accumulation of the basic PR‐1 mRNA in the bacteria‐infected leaves was intrinsically associated with the induction of ethylene biosynthesis. Treatment with 1‐aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis, strongly suppressed the induction of PR‐1 mRNA expression in the bacteria‐infected leaves. These data suggest that ethylene may function as a strong signal elicitor in the activation of PR‐1 genes, eventually mediating the plant defence response. Phytophthora capsici infection also distinctly stimulated ethylene biosynthesis, together with accumulation of PR‐1 mRNA. Expression of the basic PR‐1 mRNA was also induced in the pepper leaves by treatment with dl‐β‐amino‐n‐butyric acid or salicylic acid, but not by wounding. Treatment with methyl jasmonate, in combination with salicylic acid, strongly induced the PR‐1 transcripts. The basic PR‐1 gene expression occurred in untreated roots, flowers and green fruit of pepper but not in leaf, stem or red fruit.

Phosphorus-induced Leaf Abscission in Detached Shoots of Olive and Citrus

Previous studies have demonstrated that phosphorus, which stimulates ethylene biosynthesis, induces abscission of olive leaves directly without the involvement of ethylene. In the present study this possibility was further explored by comparing the effects of an ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), and an ethylene action inhibitor, 2,5-norbornadiene (NBD), in olive [Olea europaea (L.) `Manzanillo'] and citrus [Citrus sinensis (L.) Osbeck `Shamouti']. In olive, leaf abscission was always induced in the presence of KH2PO4 with or without AVG and NBD (alone or in combination), but it was much more pronounced when KH2PO4 was applied alone. In citrus, KH2PO4 did not induce leaf abscission in the presence of NBD during the first 48 (detached shoots) or 60 hours (leaf explants) despite the high levels of ethylene production by the tissues. Our results demonstrate that phosphorus can, at least partly, act independently of ethylene action in inducing leaf abscission in olive but not in citrus.

Gamma-Aminobutyric acid stimulates ethylene biosynthesis in sunflower.

gamma-Aminobutyric acid (GABA), a nonprotein amino acid, is often accumulated in plants following environmental stimuli that can also cause ethylene production. We have investigated the relationship between GABA and ethylene production in excised sunflower (Helianthus annuus L.) tissues. Exogenous GABA causes up to a 14-fold increase in the ethylene production rate after about 12 h. Cotyledons fed with [14C]GABA did not release substantial amounts of radioactive ethylene despite its chemical similarity to 1-aminocyclopropane-1-carboxylic acid (ACC), indicating that GABA is not likely to be an alternative precursor for ethylene. GABA causes increases in ACC synthase mRNA accumulation, ACC levels, ACC oxidase mRNA levels, and in vitro ACC oxidase activity. In the presence of aminoethoxyvinylglycine or alpha-aminoisobutyric acid, GABA did not stimulate ethylene production. We therefore conclude that GABA stimulates ethylene biosynthesis mainly by promoting ACC synthase transcript abundance. Possible roles of GABA as a signal transducer are suggested.

Induction of Enzymes Associated with Lysigenous Aerenchyma Formation in Roots of Zea mays during Hypoxia or Nitrogen Starvation.

Either hypoxia, which stimulates ethylene biosynthesis, or temporary N starvation, which depresses ethylene production, leads to formation of aerenchyma in maize (Zea mays L.) adventitious roots by extensive lysis of cortical cells. We studied the activity of enzymes closely involved in either ethylene formation (1-amino-cyclopropane-1-carboxylic acid synthase [ACC synthase]) or cell-wall dissolution (cellulase). Activity of ACC synthase was stimulated in the apical zone of intact roots by hypoxia, but not by anoxia or N starvation. However, N starvation, as well as hypoxia, did enhance cellulase activity in the apical zone, but not in the older zones of the same roots. Cellulase activity did not increase during hypoxia or N starvation in the presence of aminoethoxyvinylglycine, an inhibitor of ACC synthase, but this inhibition of cellulase induction was reversed during simultaneous exposure to exogenous ethylene. Together these results indicate both the role of ethylene in signaling cell lysis in response to two distinct environmental factors and the significance of hypoxia rather than anoxia in stimulation of ethylene biosynthesis in maize roots.

A Yeast-Derived Glycopeptide Elicitor and Chitosan or Digitonin Differentially Induce Ethylene Biosynthesis, Phenylalanine Ammonia-Lyase and Callose Formation in Suspension-Cultured Tomato Cells

Summary An elicitor preparation consisting of glycopeptides partially purified from yeast extract and the membrane- perturbing agents chitosan and digitonin were compared with respect to their effects on ethylene biosynthesis, phenylalanine ammonia-lyase (PAL) activity and callose formation in tomato cells. The yeast-derived elicitor strongly induced ethylene biosynthesis and PAL activity. The two responses were closely correlated but independent since exogenous ethylene did not induce PAL and since cobalt ions, although completely inhibiting induction of ethylene biosynthesis, did not affect elicitor-dependent induction of PAL. The yeast-derived elicitor did not induce callose formation. Chitosan and digitonin, on the other hand, strongly induced callose formation and considerably induced PAL activity but stimulated ethylene biosynthesis only weakly. When these compounds were added in combination with yeast-derived elicitor, all responses were fully induced, indicating that none of the stimuli inhibited the response to the others. The induction of ethylene biosynthesis and PAL activity by the various stimuli was completely blocked by the protein kinase inhibitor, K-252a, while induction of callose formation was not inhibited.

Elicitor-Induced Ethylene Biosynthesis in Tomato Cells

The induction of ethylene biosynthesis by an elicitor partially purified from yeast extract was studied in suspension-cultured tomato (Lycopersicon esculentum Mill.) cells. Unstimulated cells produced little ethylene during exponential growth and even less in stationary phase. Treatment with elicitor stimulated ethylene biosynthesis 10-fold to 20-fold in the exponentially growing cells and more than 100-fold in stationary cells. Activities of both 1-aminocyclopropane-1-carboxylate (ACC) synthase, measured in vitro, and ethylene-forming enzyme (EFE), measured in vivo, increased strongly in response to elicitor treatments. During exponential growth, cells contained large pools of ACC, and the elicitor stimulated ethylene biosynthesis primarily through induction of EFE. In the stationary phase, cells contained almost no ACC, and the elicitor stimulated ethylene biosynthesis primarily through its effect on ACC synthase activity. Cordycepin did not affect the increase in activity of ACC synthase but blocked that of EFE, indicating that the former was posttranscriptionally regulated, the latter transcriptionally regulated. Removal of elicitor by washing or inactivation of a biotinylated derivative of the elicitor by complexation with avidin caused a rapid cessation of the increase in ACC synthase activity, suggesting that continuous presence of stimulus is necessary for the response. Using induction of ethylene production to measure amounts of elicitor, it was found that the elicitor disappeared from the incubation medium during the course of the treatment.

Role of aminocyclopropane‐l‐carboxylic acid in ethylene release by distal tissues following localized application of ethephon in Cucurbita pepo

The application of ethephon to a single leaf of Cucurbita pepo L. cv. Trailing Marrow plants caused a huge increase in ethylene production from the treated organ and an increased rate of ethylene production from other parts of the plant. These increases were particularly marked in the shoot apex and expanding leaf. Prior treatment with aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor, blocked the increased production of ethylene at sites distant from the point of ethephon application. This strongly suggests that the increased ethylene production at these distant sites is due to ethylene biosynthesis and not a result of the translocation of ethylene released by the breakdown of ethephon at the site of application. Assays of 1‐aminocyclopropane‐l‐carboxylic acid (ACC), an ethylene precursor, showed that it increased substantially after ethephon application but was at undetectable levels in the presence of AVG. It is proposed that the application of ethephon stimulates ethylene biosynthesis, but that transport through the plants is effected by ACC which is then converted to ethylene at the shoot apex and leaves.