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ETHYLENE C 2 H 4. 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:
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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
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 Response regulator P P ATP Response Model for regulation of ethylene action
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 ETR1 ETR2 EIN4 ERS1 ERS2 Air CTR1 EIN2 EIN3 OFF
Model of ethylene signal transduction RAN1 Cu ETR1 ETR2 EIN4 ERS1 ERS2 C2H4 CTR1 EIN2 ON EIN3
Regulation of ethylene synthesis and activity Activated by high auxin fruit ripening flower senescence wounding chilling injury drought ACCS
Regulation of ethylene synthesis and activity Inhibited by ABA ethylene AVG AOA ACCS
Regulation of ethylene synthesis and activity Activated by ripening senescence ethylene ACCO
Regulation of ethylene synthesis and activity Inhibited by anaerobiosis Co2+ high temp (35+) ACCO
Regulation of ethylene synthesis and activity Ethylene level : Metabolism / Environment Silver ion CO2 (high conc at 3 to 5%) NBD (2,5-norbornadiene) DACP (diazo-cyclopentadiene) Cyclic olefins Cis butene Ethylene binding