Ethylene (H2C = CH2)—a gas that is formed in plant organs, being an inhibiting hormone and an auxin antagonist. It was found in plants and fungi and does not occur in bacteria, algae, and animals. It is considered the maturation and aging hormone since it stimulates apoptosis.
At low concentrations (0.04–1.0 μl) it shows strong morphogenetic effects. It was described in 1901 by Neliubov, which demonstrated the role of ethylene in inhibiting stem elongation, thickening and hori-
zontal orientation. In the 20s of the XXth century, it was found that ethylene accelerates fruit ripening.
Biosynthesis
Ethylene in higher plants is synthesized in the presence of light, from methionine, with 1 amino cyclo-propane-1-carbonate (ACC) as a precursor, which can serve as a transportation form.
Transport
Ethylene diffuses freely through the intercellular spaces.
Mechanism of action
Ethylene action on biological processes is very fast, which leads to the idea that like other phytohormones, ethylene has a signaling role.
Biological significance
• causes epinasties;
• delays growth and development;
• stimulates organ aging;
• accelerates fruit ripening and their detachment (Fig. 7.28);
• contributes to flower, bud, and leaf detachment;
• blocks the growth of leaves, plant elongation, and mitosis;
• slows down polar auxin transport and removes apical dominance;
• switches the direction of growth from the longitudinal one to the transversal one, contributing to the thickening of the stems
• increases membrane permeability, stimulating respiratory contact between enzymes and substrates;
• these effects are removed when the concentration of CO2 increases.
Practical applications
It is used to preserve fruits during winter. Other natural inhibitors such as the β inhibitor, phlorizin, coumarin, cinnamic acid, scopoletin, etc., are poorly studied.