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ETHYLENE C2H4 Plant Hormone Regulatory functions in growth and development Stimulators or inhibitors Physiological Effects of Ethylene Normal growth and development Stress response biotic and abiotic Ethylene in organisms Animal Production: not normal Effect: 82+ % as anesthetic in 15 second ignition at humidity lower than 56 % Ethylene in organisms Bacteria Bacterial rot of cauliflower Fungi Pennicilium digitatum Aspergillus flavus Alternaria solani Ethylene in organisms Neljubov (1901): Gaseous hydrocarbon olefin Triple response in etiolated pea seedlings Cousins (1910): Orange and banana in the same shipment Gane (1934): Ethylene as a natural plant product Ethylene Diffusibility Easily released from tissues Diffuse through the gas phase intercellular and outside Rapid and sensitive response system Active concentration: 10 ppb Ethylene Biosynthetic Pathway (1979) Alternative pathway Peroxidation of long chain fatty acids eg. Linolenic acid Met SAM ACC Ethylene N-Malonyl ACC (Nonvolatile compound) Synthesized in most tissues of almost all higher plants Easily isolated and quantified Also found in gymnosperms lower plants bacteria Ethylene Production Environmental effect * O2 O2 C2H4 (except rice) * Temperature apple T P peanut / plum T P * CO2 apple P sweet potato P bean no effect Ethylene Production Other hormones Auxin: activate production: 10x GA: activate in bean citrus blueberry inhibit in soybean seedling CK: activate in bean blueberry sorghum ABA: activate in leaf and fruit inhibit in seed and soybean seedling Enzymes in Ethylene Biosynthetic Pathway ACC Synthase or ACCS Rate-limiting step of pathway SAM to ACC ACCS level Hormone levels Growth environment Physiological environment Developmental environment ACC Synthase or ACCS Amino acid sequences of tomato, apple, squash and zucchini Share 40% identity and 80% similarity Contain 7 highly conserved regions ACC Synthase or ACCS Different isoforms Encoded by a multigene family ACC oxidase or ACCO Require aerobic conditions ACC to Ethylene ACCO level: environmental stresses ACC oxidase or ACCO Ethylene-forming enzyme : EFE A ripening-induced cDNA confers yeast an oxidase activity ACC-N-Malonyl transferase ACCM Autoregulation to prevent ethylene overproduction Storage / inactive form of ACC Ethylene transport Diffusion (short distance) ACC (long distance) Ethylene metabolism oxidation and hydrolysis Ethylene oxide ethylene glycol Glucose conjugates of ethylene glycol CO2 Ethylene Action CS2 a potent inhibitor of ethylene oxidation No effect on ethylene responses Action of ethylene ……..? *Ethylene effects not general for all plants *A signal of environmental changes or physiological changes *Manifold effects mediated by induction of new proteins *regulator or modulator or coordinator of processes Ethylene Perception by receptors Signal transduction Responses Ethylene binding Ethylene receptors Hypothesis Reversibly binding to a receptor through a transition metal Ethylene-binding components Membrane bound Solubility Chromatographic behaviors Sensitive to heat protease sulfhydryl agent Nature of protein Ethylene-binding proteins (EBP): Various tissues and plants tobacco, bean, Arabidopsis Specific High affinity Saturable Characteristics of receptor binding moiety facing the apoplast Ethylene binding protein EBP of Phaseolus vulgaris Heterotrimer or Heterotetramer Subunits of ca. 12 to 14 kDa Integral membrane protein ETR Receptor found in Arabidopsis Dimer Subunits of 79 to 83 kDa 3 transmembrane segments Classes of ethylene-binding proteins - High rate constant of association/dissociation - Very low rate constant of association/dissociation Classes of ethylene-binding proteins 2 classes rice tomato pea Arabidopsis Class 2: bean (Phaseolus) mungbean Ethylene-insensitive mutant Arabidopsis Decreased ethylene binding Low concentrations of ethylene binding protein Antibody against Phaseolus EBP Recognize homologous proteins from pea rice Arabidopsis Signal transduction pathway Signaling pathway A two-component system bacteria common / well-characterized key mechanism protein phosphorylation 2-component signaling pathway Histidine kinase for sensing / transducing extracellular signals 2-component signaling pathway Phosphotransfer between two types of signal transducers Sensory kinase (input & kinase domains) Response regulator (receiver & output domains) Ethylene signal transduction pathway Genetic and biochemical studies Similar to a bacterial two-component system Conserved residues for kinase activity in EBP Phosphorylation of EBP upon binding of ethylene Ethylene kinase P Response regulator P ATP Model for regulation of ethylene action Response •Ethylene binding •Autophosphorylation of kinase •Phosphate transfer to a response regulator •Release of an activated ligand or activation of soluble factor •Derepression of genes involved in ethylene responses Model of ethylene signal transduction RAN1 Cu Air ETR1 ETR2 EIN4 ERS1 ERS2 CTR1 EIN2 EIN3 OFF Model of ethylene signal transduction RAN1 Cu C2H4 ETR1 ETR2 EIN4 ERS1 ERS2 CTR1 EIN2 EIN3 ON Model of ethylene signal transduction Regulation of ethylene synthesis and activity Activated by high auxin ACCS fruit ripening flower senescence wounding chilling injury drought Regulation of ethylene synthesis and activity Inhibited by ABA ACCS ethylene AVG AOA Regulation of ethylene synthesis and activity Activated by ACCO ripening senescence ethylene Regulation of ethylene synthesis and activity Inhibited by anaerobiosis ACCO Co2+ high temp (35+) Regulation of ethylene synthesis and activity Ethylene level : Metabolism / Environment Ethylene binding Silver ion CO2 (high conc at 3 to 5%) NBD (2,5-norbornadiene) DACP (diazo-cyclopentadiene) Cyclic olefins Cis butene Commercial uses of ethylene - Ethylene - Acetylene - ACC - Ethylene-releasing compounds Ethephon / Ethrel ******************************************* - Ventilation with hypobaric pressure - Silver - AVG / AOA - KMnO4 Ethylene / cell expansion / triple response thicker and shorter Root/hypocotyl reorientation of cell expansion