1. Ethylene
Abscission of fruits, flowers and leaves

2. The Discovery of Ethylene
The oldest identified growth regulator
Was used by the ancient Egyptians to cause fig ripening
The Chinese burned incense in closed rooms to cause pear ripening
Discovered in 1901 by Dimitry Neljubow
In 1910 H. H. Cousins showed that plants can produce their own ethylene
Discovery of Ethylene's role in abscission was in 1917 by S Doubt
In 1934 ethylene was shown as a natural plant product

3. Functions of Ethylene Stimulates shoot & root growth & differentiation
Stimulates the release of dormancy
May have a role in adventitious root formation
Stimulates bromiliad flower induction
Induction of femaleness in dioecious flowers
Stimulates flower opening
Stimulates flower & leaf senescence
Stimulates fruit ripening
Stimulates leaf, fruit and flower abscission

4. Ethylene transport Transported as a gas Diffuses through the airspace
Transported in the cytosol
Travels from cell to cell in the symplast and phloem

5. Measurement of Ethylene
Epinasty of leaves
Flower senescence
Root hair formation
Leaf abscission
Triple response
Gas chromatography

6. Biosynthesis of Ethylene
Ethylene is produced from L-methionine in higher plants
Methionine is activated by ATP to form S-sdenosylmethionine
ACC is the rate limiting step of ethylene production and its activity is regulated by factors such as wounding, drought stress, flooding and auxin

7. Stress induced Ethylene
Ethylene is the stress hormone
Wounding
Flooding
Drought
Chilling
Heating

8. Three phases of leaf abscission
Leaf maintenance phase
Shedding induction phase
Shedding phase

9. Ethylene’s Affects Cross section of a cabbage
Stored in a room containing apples
Ethylene produced from the apples caused abscission of the leaves from the stalk, even though the cabbage was immature

10. Ethephon O ll
Cl-----CH2----CH2----P----OH + OH-  CH2===CH2 + H2PO4- + Cl- l O-
Ethephon Ethylene
Stable at low pH, but at neutral or high pH, breaks down to give off ethylene
Mixing with water is a convenient method of exposing plants to high doses of ethylene

11. Characterization of a non-abscission mutant in Lupinus angustifolius. I. Genetic and Structural aspects
Jon Clements and Craig Atkins
American Journal of Botany 88(1): 31-42, 2001

12. Lupinus angustifolius (Abs-)
Spontaneous mutant (Abs-) that does not abscise any organ, but still maintains normal patterns of growth and senescence
A recessive single gene mutation
This mutant is specific to abscission, and may be caused by a lack or delay in the expression of hydrolytic enzymes which are specifically associated with abscission zone differentiation and separation

13. Biotechnology Relevance
Delays in fruit ripening
Delays in petal fading
Delays in abscission
Abscission limits yield and fiber quality of cotton