Ethylene Abscission of fruits, flowers and leaves

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

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

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

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

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

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

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

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

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

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

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

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