Ethylene Biosynthesis In Higher Plants Research Articles

SOYBEAN SEEDLING ROOT GROWTH PROMOTION BY 1-AMINOCYCLOPROPANE-1-CARBOXYLATE DEAMINASE-PRODUCING PSEUDOMONADS

Pseudomonad producing 1-aminocyclopropane-1-carboxylate (ACC) deaminase (E.C.4.1.99.4) has been known to promote plant growth by lowering ethylene biosynthesis in higher plants, which can be induced by indole-3-acetic acid (IAA) production. The objective of this study was to examine the ability of IAAproducing Pseudomonas isolated from local soil environment (rhizosphere of soybean grown in Plumbon's agricultural area<br />in Cirebon, West Java, Indonesia) to promote soybean root growth in relation to their ACC deaminase activities. The experiments were conducted in growth room and Laboratory of Soil Biology Research, Indonesian Soil Research Institute, Bogor, from January to August 2008. Soybean seeds were inoculated by immersing the seeds for 1 hour in bacterial cell suspension containing approximately 108-109 cells ml-1. The seeds were then germinated<br />for 2 days before planting in growth pouches containing sterilized distilled water. All treated and untreated seeds were grown for 7 days in growth room at 24°C with 1300 lux of light intensity for 12-hour followed by a 12-hour dark period at 22°C. ACC deaminase activity of the isolates was assayed based on their ability to grow in Dworkin-Foster’s salt minimal medium containing ammonium sulfate or ACC as a source of nitrogen. Thirteen out of 81 isolates tested significantly increased soybean root length and weight, up to 50% from untreated plants. Of 13 isolates, 11 demonstrated ACC deaminase activities. Two isolates that did not show ACC deaminase activities had lower capacity to produce IAA. The results suggest that the effectiveness of IAA producing Pseudomonas in promoting the growth of the soybean seedlings is associated with their ACC deaminase activities or they produce IAA at low levels.

SOYBEAN SEEDLING ROOT GROWTH PROMOTION BY 1-AMINOCYCLOPROPANE-1-CARBOXYLATE DEAMINASE-PRODUCING PSEUDOMONADS

Pseudomonad producing 1-aminocyclopropane-1-carboxylate (ACC) deaminase (E.C.4.1.99.4) has been known to promote plant growth by lowering ethylene biosynthesis in higher plants, which can be induced by indole-3-acetic acid (IAA) production. The objective of this study was to examine the ability of IAAproducing Pseudomonas isolated from local soil environment (rhizosphere of soybean grown in Plumbon's agricultural area<br />in Cirebon, West Java, Indonesia) to promote soybean root growth in relation to their ACC deaminase activities. The experiments were conducted in growth room and Laboratory of Soil Biology Research, Indonesian Soil Research Institute, Bogor, from January to August 2008. Soybean seeds were inoculated by immersing the seeds for 1 hour in bacterial cell suspension containing approximately 108-109 cells ml-1. The seeds were then germinated<br />for 2 days before planting in growth pouches containing sterilized distilled water. All treated and untreated seeds were grown for 7 days in growth room at 24°C with 1300 lux of light intensity for 12-hour followed by a 12-hour dark period at 22°C. ACC deaminase activity of the isolates was assayed based on their ability to grow in Dworkin-Foster’s salt minimal medium containing ammonium sulfate or ACC as a source of nitrogen. Thirteen out of 81 isolates tested significantly increased soybean root length and weight, up to 50% from untreated plants. Of 13 isolates, 11 demonstrated ACC deaminase activities. Two isolates that did not show ACC deaminase activities had lower capacity to produce IAA. The results suggest that the effectiveness of IAA producing Pseudomonas in promoting the growth of the soybean seedlings is associated with their ACC deaminase activities or they produce IAA at low levels.

Bacteria in combination with fertilizers promote root and shoot growth of maize in saline-sodic soil.

Salinity is the leading abiotic stress hampering maize ( Zea mays L.) growth throughout the world, especially in Pakistan. During salinity stress, the endogenous ethylene level in plants increases, which retards proper root growth and consequent shoot growth of the plants. However, certain bacteria contain the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which converts 1-aminocyclopropane-1-carboxylic acid (an immediate precursor of ethylene biosynthesis in higher plants) into ammonia and α-ketobutyrate instead of ethylene. In the present study, two Pseudomonas bacterial strains containing ACC-deaminase were tested separately and in combinations with mineral fertilizers to determine their potential to minimize/undo the effects of salinity on maize plants grown under saline-sodic field conditions. The data recorded at 30, 50 and 70 days after sowing revealed that both the Pseudomonas bacterial strains improved root and shoot length, root and shoot fresh weight, and root and shoot dry weight up to 34, 43, 35, 71, 55 and 68%, respectively, when applied without chemical fertilizers: these parameter were enhanced up to 108, 95, 100, 131, 100 and 198%, respectively, when the strains were applied along with chemical fertilizers. It can be concluded that ACC-deaminase Pseudomonas bacterial strains applied alone and in conjunction with mineral fertilizers improved the root and shoot growth of maize seedlings grown in saline-sodic soil.

Cloning and analysis of cross-intron genomic gene encoding ACO in Paeonia suffruticosa Andr.

The last step of ethylene biosynthesis in higher plants is to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene by ACC oxidase (ACO). In our investigation, a cross-introns genomic DNA gene encoding ACC oxidase, PsgACO, was isolated from Paeonia suffruticosa. It revealed that PsgACO (FJ855434) has 1281 bases, containing four exons and three introns, encoding 312 amino acids. The four exons stretched from 1 to 105, 217 to 434, 592 to 925 and 1000 to 1281 bases. A splicing junction sequence of all the exon-introns conformed to the GT-AG rule in the cross-intron genomic DNA sequence of the ACO gene. PsgACO showed high homology to many characterized ACC oxidases both at the nucleic acid and amino acid levels. As well, twelve amino acid residues were conserved among many ACOs from other species. A phylogenetic tree analysis indicated that the amino acid of ACOs is quite conserved among the different eudicots. The phylogenetic tree showed that both the tree peony and herbaceous peony are quite isolated taxa. Bioinformatic analysis showed that the molecular weight of ACO is 35.29 kD, with a theoretical pI of 5.25. It is a non-secrete, stable hydrophilic protein, located in the cytoplasm.

Regulation of ethylene biosynthesis at the level of 1-aminocyclopropane-1-carboxylate oxidase (ACO) gene

Ethylene, a gaseous plant hormone regulates essentially all physiological processes during the plant’s life cycle. The practical implications of ethylene biosynthesis regulation for plant improvement have supported the continuous basic research on dissecting the structure of genes encoding ethylene biosynthetic enzymes, their differential expression patterns, and mechanisms underlying their transcriptional activity. ACC oxidase (ACO) is involved in the final step of ethylene production in plant tissues. In various plants several ACO isoforms have been isolated which are encoded by a multigenic family. There is a strong evidence that ACO gene expression is positively correlated to the ethylene production rates and its multiple isoforms are under development and environmental control. Thus, the regulation of ACO gene activity may act either as an additional or in several cases also as a main level for controlling ethylene biosynthesis in higher plants. This review summarizes in detail the knowledge about organization and gene structure, and transcriptional expression of ACO genes from different plant species. The perspectives of manipulating ACO gene as a method in biotechnological modification of ethylene synthesis are also discussed.

Heterologous expression analyses of rice OsCAS in Arabidopsis and in yeast provide evidence for its roles in cyanide detoxification rather than in cysteine synthesis in vivo

While most dicot plants produce little ethylene in their vegetative stage, many monocots such as rice liberate a relatively large amount of ethylene with cyanide as a co-product in their seedling stage when etiolated. One of the known functions of β-cyanoalanine synthase (CAS) is to detoxify the co-product cyanide during ethylene biosynthesis in higher plants. Based on a tryptic peptide sequence obtained from a partially purified CAS activity protein preparation in etiolated rice seedlings, the full-length putative rice CAS-encoding cDNA sequence (OsCAS), which is homologous to those O-acetylserine sulphydrylase (OASS) genes, was cloned. Unlike most of the CAS genes reported from dicots, the transcription of OsCAS is promoted by auxins but suppressed by ethylene. To address the function and the subcellular localization of this gene product in planta, a binary vector construct consisting of this gene appended with a yellow fluorescent protein-encoding sequence was employed to transform Arabidopsis. Specific activities on CAS and OASS of the purified recombinant protein from transgenic Arabidopsis were 181.04 μmol H2S mg−1 protein min−1 and 0.92 μmol Cys mg−1 protein min−1, respectively, indicating that OsCAS favours CAS activity. The subcellular localization of OsCAS was found mostly in the mitochondria by immunogold electron-microscopy. Chemical cross-linking and in-gel assay on a heterodimer composed of functional and non-functional mutants in a yeast expression system on OsCAS suggested that OsCAS functions as a homodimer, similar to that of OASS. Despite the structural similarity of OsCAS with OASS, it has also been confirmed that OsCAS could not interact with serine-acetyltransferase, indicating that OsCAS mainly functions in cyanide detoxification.

Prospective Use of 1-Aminocyclopropane-1-Carboxylate Deaminase-Producing Bacteria for Plant Growth Promotion and Defense against Biotic and Abiotic Stresses in Peat-Soil-Agriculture

The 1-aminocyclopropane-1-carboxylate (ACC) deaminase (EC4.1.99.4) is an enzyme produced by some soil bacteria to degrade ACC (the immediate precursor of ethylene) to reduce ethylene biosynthesis in higher plants. Increased concentrations of ethylene in plant tissues, which are triggered by various biotic and abiotic stresses, inhibits plant growth and weakens the plant defense against the stressors. Various findings on the successful use of ACC deaminase producing bacteria for plant growth under unfavorable soil conditions are inspiring their use in tropical peat-soil-agriculture, which possesses bio-physical constraints. It has been proven that inoculation of plants with ACC deaminase producing bacteria decreased ethylene inhibition generated by unfavorable environmental conditions, such as nutrient shortage, flooding, drought, high salts, and the presence of heavy metals and organic pollutants. Understanding the mechanisms by which ACC deaminase-producing bacteria act to reduce plant stress and the fitness of bacterial traits with the properties and constraints of peat-soils becomes a key to utilize these bacteria in improving crop productivity. The bacteria may ameliorate plant stress as well as promote plant growth under seasonal bio-physical changes of peat-soils that are usually encountered in the field.

Perspective of plant growth promoting rhizobacteria (PGPR) containing ACC deaminase in stress agriculture

Ethylene is a gaseous plant growth hormone produced endogenously by almost all plants. It is also produced in soil through a variety of biotic and abiotic mechanisms, and plays a key role in inducing multifarious physiological changes in plants at molecular level. Apart from being a plant growth regulator, ethylene has also been established as a stress hormone. Under stress conditions like those generated by salinity, drought, waterlogging, heavy metals and pathogenicity, the endogenous production of ethylene is accelerated substantially which adversely affects the root growth and consequently the growth of the plant as a whole. Certain plant growth promoting rhizobacteria (PGPR) contain a vital enzyme, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which regulates ethylene production by metabolizing ACC (an immediate precursor of ethylene biosynthesis in higher plants) into alpha-ketobutyrate and ammonia. Inoculation with PGPR containing ACC deaminase activity could be helpful in sustaining plant growth and development under stress conditions by reducing stress-induced ethylene production. Lately, efforts have been made to introduce ACC deaminase genes into plants to regulate ethylene level in the plants for optimum growth, particularly under stressed conditions. In this review, the primary focus is on giving account of all aspects of PGPR containing ACC deaminase regarding alleviation of impact of both biotic and abiotic stresses onto plants and of recent trends in terms of introduction of ACC deaminase genes into plant and microbial species.

Tyr152 plays a central role in the catalysis of 1-aminocyclopropane-1-carboxylate synthase

1-Aminocyclopropane-1-carboxylate (ACC) synthase is a key enzyme in the regulation of ethylene biosynthesis in higher plants. To investigate the catalytic significances of two conserved tyrosine residues, Tyr151 and Tyr152, of a tomato ACC synthase isozyme (LeACS2), five ACC synthase mutants (Y151F, Y151G, Y152F, Y152G, and Y151F/Y152F) were constructed and over-expressed in Escherichia coli. Subsequent kinetic analysis indicated that these point mutations in mutants Y152F, Y152G, and Y151F/Y152F, either reduced the catalytic efficiency more than 98% or fully inactivated ACC synthase, while Y151F and Y151G mutants reduced the enzymatic activities by 27% and 83%, respectively. It is therefore concluded that Tyr152, especially its hydroxyl group, plays an essential role in the catalysis of ACC synthase. Thus, a revised catalytic model is hereby proposed for functional ACC synthase.

The GUS reporter-aided analysis of the promoter activities of Arabidopsis ACC synthase genes AtACS4, AtACS5, and AtACS7 induced by hormones and stresses

Ethylene biosynthesis in higher plants is regulated developmentally and environmentally. To investigate the regulation of ACC synthase gene expression, the promoters of Arabidopsis ACS genes, AtACS4, AtACS5, and AtACS7, were fused to a GUS reporter gene, and the recombinant transgenes were introduced into Arabidopsis to produce three groups of AtACS::GUS transgenic plants. Histochemic and fluorometric study of these transgenic plants revealed that promoters of AtACS4, AtACS, and AtACS7 are all active in dark-germinated seedlings. AtACS5 has the highest promoter activity in leaves of 2-week-old light-grown seedlings among the three AtACS genes studied. In the mature leaves, AtACS4 and AtACS7 genes are expressed in both veins and areoles, whereas AtACS5 is expressed at a higher level in the areoles and epidermal cells surrounding trichomes. The promoter activities of all these AtACS genes are found in the reproductive organs. AtACS5 and AtACS7 are highly expressed in petals, sepals, carpels, stamens, cauline leaves, inflorescence stems, and siliques, while AtACS4 expression is undetectable in the petals of open flowers. All three AtACS genes are expressed in root tissue. In the 2-week-old light-grown Arabidopsis, the AtACS4 promoter is responsive to the plant hormones IAA, ethylene, and ABA, and to darkness and wounding; the AtACS5 promoter to IAA, ABA, salt, high temperature, and wounding; and the AtACS7 promoter to GA3, ethylene, and ABA, and to darkness and salt. Low-temperature treatment abolishes the darkness-induced AtACS7 gene expression, but not that of AtACS4. Each AtACS gene has a unique expression profile during growth and development. It appears that at any developmental stage or any growth period of Arabidopsis, there is always a member of AtACS multigene family that is actively expressed.

Regulation of ethylene biosynthesis in higher plants by carbon dioxide

Abstract Elevated CO2 levels used with or without reduced O2 levels regulate many biochemical and physiological processes in higher plants, among them ethylene biosynthesis. The mode of action of elevated CO2 in the regulation of ethylene biosynthesis is still a subject of much debate. Various hypotheses have been put forward to explain its mode(s) of action and most of them have pointed out that CO2 regulates ethylene biosynthesis, at least in part, by counteracting ethylene action. This is thought to be mainly through the regulation of 1-aminocyclopropane-1-carboxylate (ACC) synthase, presumably the rate-limiting enzyme in the ethylene biosynthetic pathway, and in some instances ACC oxidase. The present review brings together recent developments on the biochemical, physiological and molecular bases for the regulation by CO2 of ethylene biosynthesis in higher plants. The mode of activation of ACC oxidase by CO2 is also discussed.

Identification of two new members of the l-aminocyclopropane-l-carboxylate synthase-encoding multigene family in mung bean

The key enzyme regulating ethylene biosynthesis in higher plants is l-aminocyclopropane-l-carboxylate (ACC) synthase. In mung bean (MB), the existence of three genes encoding this enzyme has previously been reported [Botella et al., Plant Mol. Biol. 18 (1992) 793–797], one of which corresponds to a full-length indole-3-acetic acid-inducible cDNA [Botella et al., Plant Mol. Biol. (1992) 425–436], In this paper we report the cloning of two new genomic sequences coding for ACC synthase in MB ( MAC-4 and MAC-5). MAC-4 is 1340 bp long and encodes 388 amino acids (aa) while MAC-5 is 1393 bp long and encodes for 391 aa. Genomic Southern analysis suggests the existence of only one copy of each gene in the genome.

Identification of a unique isoform of 1-aminocyclopropane-1-carboxylic acid synthase by monoclonal antibody

1-Aminocyclopropane-1-carboxylic acid (ACC) synthase (EC 4.4.1.14) is a key enzyme regulating ethylene biosynthesis in higher plants. A monoclonal antibody (mAb T20C) that immunoprecipitates the ACC synthase activity from tomato pericarp tissue extracts revealed that mAb T20C immunodecorates an approximately 67-kDa polypeptide. On isoelectric focusing gels, ACC synthase activity in cell-free preparations was resolved into three distinct activity peaks with pI values 5.3, 7, and 9. mAb T20C specifically recognized the pI 7 form of the enzyme on electrophoretic transfer (Western) blots. When analyzed by sodium dodecyl sulfate gel electrophoresis under reducing conditions, the eluted pI 7 form was confirmed to migrate as a polypeptide of 67 kDa. The 67-kDa pI 7 isoform is a previously undescribed form of ACC synthase.

Recent advance in studies of ethylene biosynthesis in higher plants

Recent advance in studies of ethylene biosynthesis in higher plants

Biosynthesis of ethylene in higher plants: the metabolic site of inhibition by phosphate*

Abstract. Phosphate inhibited endogenous as well as 1‐aminocyclopropane‐1‐carboxylic acid (ACC)‐stimulated ethylene synthesis in slices of tomato fruit, segments of carrot root and pea hypocotyls. ACC concentrations of up to 10 mol m−3 did not overcome this inhibition. Phosphate inhibited the conversion of 14C ACC to ethylene in tomato fruit and vegetative tissue. Enzymatic conversion of ACC to ethylene by pea seedling homogenate was also inhibited by phosphate with a linear concentration dependency. The formation of ACC from S‐adenosylmethionine (SAM) by extracts of pink tomatd fruit was slightly, but not significantly, affected by phosphate. However, the SAM to ACC conversion was greater when extracts from tomato fruit were made in phosphate rather than in HEPES‐KOH buffer. Non‐enzymatic ethylene synthesis from ACC in a model system was stimulated by phosphate. We suggest that phosphate is an inhibitor of ethylene biosynthesis in higher plants and that one site of its control is the conversion of ACC to ethylene.