Ethylene plant hormone

Pinosylvin and pinosylvin monomethyl ether are formed in the reaction zone in Pinus spp. as a response to fungus infections (57, 61). There is also an interesting correlation between the stilbene production in Pinus radiata and the presence of ethylene (plant hormone) in the wood (105, 106). The processes involved in heartwood formation and the formation of phenolic compounds in reaction zones have been extensively investigated and reviewed by Hillis (59). 

Ethylene occurs naturally in small amounts as a plant hormone Hormones are substances that act as messengers to regulate biological processes Ethylene IS involved in the ripening of many fruits in which it IS formed in a complex series of steps from a com pound containing a cyclopropane ring... 

For a review see Ethylene—An Unusual Plant Hormone in the April 1992 issue of the Journal of Chemical Education (pp 315-318)... 

An alkene, sometimes caJled an olefin, is a hydrocarbon that contains a carbon-carbon double bond. Alkenes occur abundantly in nature. Ethylene, for instance, is a plant hormone that induces ripening in fruit, and o-pinene is the major component of turpentine. Life itself would be impossible without such alkenes as /3-carotene, a compound that contains 11 double bonds. An orange pigment responsible for the color of carrots, /3-carotene is a valuable dietary source of vitamin A and is thought to offer some protection against certain types of cancer. 

B. Jackson J. E. Summers L. A. C. J. Voesenek, Potamogeton Pectinatus A Vascular Plant that Makes No Ethylene. In Biology and Biotechnology of the Plant Hormone Ethylene A. K. Kanellis, C. Chang, H. Kende, D. Grierson, Eds. Kluwer Academic Publishers Netherlands, 1997. 

Boiler, T. (1991). Ethylene in pathogenesis and disease resistance. In The Plant Hormone Ethylene, eds. A. K. Matoo and J. C. Suttle, pp. 293-314. Boca Raton, FL CRC Press. 

Ethylene is now considered to be one of the main plant-hormones involved in fruit development. Many responses formerly believed to result from the presence of auxins are now ascribed to induced ethylene production.425 The biosynthetic pathway for formation of ethylene from methionine, in a wide variety of plant tissues, including shoots of mung bean,426 tomato,427 and pea427 carrot427 and tomato428 roots and the fruits of apple,429,430 tomato,427 and avocado,427 has been elucidated, and is as follows. 

Cyclization. A second kind of reaction is represented by the conversion of S-adenosylmethionine to aminocyclopropanecarboxylic acid, a precursor to the plant hormone ethylene (see Chapter 24).159 The quinonoid intermediate cyclizes with elimination of methylthioadenosine to give a Schiff base of the product (Eq. 14-27).160-161a The cyclization step appears to be a simple SN2-like reaction.162... 

Ethylene not only hastens the ripening of fruit but also tends to promote senescence in all parts of plants. Its signaling mechanisms are the best-known for any plant hormone.368 369 Tire synthesis and action of ethylene are discussed in Chapter 24, Section D,4. Ethylene is metabolized slowly in plants by oxidation to ethylene oxide. The latter is hydrolyzed to form ethylene glycol, which is metabolized further to C02 (Eq. 30-3). 

Some common plant hormones. All of these hormones are low-molecular-weight compounds. One hormone, ethylene, is a gas. 

Synthesis of ethylene, a gaseous plant hormone involved in fruit ripening and flower senescence. 

McKeon, T.A. Yang, S.F. (1987). Biosynthesis and metabolism of ethylene. In Plant Hormones and their Role in Plant Growth and Development, ed. P.J. Davies, pp. 94-112. Dordrecht Martinus Nijhoff. 

The simplest unsaturated carbon compound, ethylene, exerts a major influence on many if not all aspects of plant growth and development. Although ethylene is a gas at physiological temperatures and pressures, it is now recognized as a plant hormone because it is a natural product of metabolism, acts in trace amounts and is neither a substrate nor cofactor in reactions which are associated with major developmental plant processes. Whether or not ethylene meets all the standard criteria established for hormones, there is no question that this gas is a powerful natural regulating substance in plant metabolism, and that it acts and interacts with other recognized plant hormones. With the advent of gas chromatography, ethylene has become the simplest plant hormone to assay since it is evolved from the tissues and requires no extraction or purification prior to analysis. 

Plants under water stress are known to produce increased amounts of ethylene, show a rise in ABA and a decline in endogenous cytokinins (52,53). Other plant hormones are also probably involved in the response to water stress and other stress and wounding actions. The surge of ethylene production upon stress may therefore represent a response to a disturbance of the hormonal balance in tissues. The dampened oscillation curve for wound ethylene production may reflect the dynamic return of the disturbed hormonal system to a proper hormonal balance under the new tissue conditions, and thus may also reflect a healing phenomenon. 

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