ETHYLENE C 2 H 4 Plant Hormone Regulatory

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: 82+ % as anesthetic in 15 second ignition at humidity lower than 56%

Ethylene in organisms 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 *O 2 C 2 H 4 (except rice( *Temperature apple T P peanut / plum T P *CO 2 apple P sweet potato P bean no effect

Ethylene Production Other hormones Auxin: activate production: 10 x 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 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 c. DNA 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 CO 2

Ethylene Action CS 2 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 k. Da Integral membrane protein

ETR Receptor found in Arabidopsis Dimer Subunits of 79 to 83 k. Da 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 RAN 1 Cu Air ETR 1 ETR 2 EIN 4 ERS 1 ERS 2 CTR 1 EIN 2 EIN 3 OFF

Model of ethylene signal transduction RAN 1 Cu C 2 H 4 ETR 1 ETR 2 EIN 4 ERS 1 ERS 2 CTR 1 EIN 2 EIN 3 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 Co 2+ high temp (35+)

Regulation of ethylene synthesis and activity Ethylene level : Metabolism / Environment Ethylene binding Silver ion CO 2 (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 - KMn. O 4

Ethylene / cell expansion / triple response thicker and shorter Root/hypocotyl reorientation of cell expansion