HORMONE PHYSIOLOGY AND SIGNAL TRANSDUCTION Huseyin Tombuloglu, Phd. GBE 304 Spring 2015

ETHYLENE The Gaseous Hormone

Figure 22.1 Triple response of etiolated pea seedlings

Ethylene Exists as a gas. Caused such things as sprouting, fruit ripening, leaf abscission, and flowering.

Ethylene Only recognized as a plant hormone as late a 1960s. Ethylene is a gas with a simple chemical structure… Very potent and important regulator of plant growth!

DURING THE NINETEENTH CENTURY, when coal gas was used for street illumination, it was observed that trees in the vicinity of streetlamps defoliated more extensively than other trees. Because coal gas and air pollutants affect plant growth and development, and ethylene was identified as the active component of coal gas Cousins reported that “emanations” from oranges stored in a chamber caused the premature ripening of bananas when these gases were passed through a chamber containing the fruit.

Functions of Ethylene Fruit ripening….bananas for example. Seed germination. Petal and leaf abscission. Wound healing. Influences cell divisions and growth. Floral initiation in some plants.

In the grocery store… What do you think ethylene does?

Functions of Ethylene Ethylene will speed up maturation of fruit tissues….plants will naturally produce ethylene in fruit tissues as they ripen. Apples for example release natural ethylene as they ripen.

Functions of Ethylene Natural, or endogenous, ethylene produced by plants will cause: Abnormal development in etiolated (grown in the dark…no pigments) seedling. Speed up fruit and leaf abscission. Floral initiation in some plant species…uniform flowering in pineapple. Speed up fruit maturation/ripening.

Ethylene production is regulated by internal signals during development and by various biotic and abiotic stresses, such as pathogen invasion, flooding, freezing, and drought. Isolation of mutants in the plant Arabidopsis thaliana affecting ethylene responses has led to the identification of ethylene receptors and several downstream components in the ethylene signal transduction pathway. The integral membrane protein ETHYLENE INSENSITIVE2 (EIN2), which is supposed to act between the soluble serine/threonine kinase CTR1 and the EIN3/EIL family of transcription factors, is a central and most critical element of this pathway.

Ethylene and horticulture Horticulturally, ethylene is applied as a gas in enclosed chambers to increase fruit ripening. Liquid chemicals that transform into ethylene in plants have been developed and are used in a broad range of applications…

Ethylene and horticulture Ethephon…(2-chloroethyl)phosphonic acid) Used for uniform ripening of pineapple and tomato. Change in sex expression in cucumbers. Initiates pistilate flowers in mostly staminate plants.

Figure Inhibition of flower senescence by inhibition of ethylene action

Figure Schematic view of the roles of auxin and ethylene during leaf abscission