BIOLOGY Volume 2 - A Guide to General Biology - 2004

16. PLANT COORDINATION AND REGULATION

16.2. Plant Growth Substances

16.2.9. Ethylene (Ethene)

Discovery of the Plant Growth-Regulating Properties of Ethylene

By the early 1930s, it was known that ethylene gas accelerates the ripening of citrus fruits and exerts various effects on plant growth. It was later established that a gas with similar effects is produced by certain fruits, such as bananas. In 1934, it was discovered that ripening apples release ethylene itself, and even later it was shown that ethylene is produced by A wide variety of ripe fruits and other plant Organs, especially when damaged. Trace amounts of ethylene are emitted by virtually all plant organs.

Structure of Ethylene

The structural formula of ethylene is shown in Fig. 16.25.

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Fig. 16.25. Structural formula of ethylene (ethene).

Synthesis and Distribution of Ethylene

As noted above, ethylene is produced by many, and possibly all, plant organs. Although ethylene is a gas, it generally does not diffuse freely through the internal air spaces of a plant because it rapidly escapes into the surrounding environment. However, it has been demonstrated that a Water-soluble precursor of ethylene is transported via the xylem from waterlogged roots to the shoots.

Effects of Ethylene

Ethylene is best known for its stimulating effect on fruit ripening, which is accompanied by a sharp increase in Respiration rate (the so-called Climacteric phase) in certain species (Section 16.3.5). Like ABA, it sometimes acts as a growth inhibitor and can induce the abscission of fruits and leaves. Its effects are summarized in Table 16.4.

Practical Applications OF Ethylene

Ethylene induces flowering in pineapples and stimulates the ripening of tomatoes and citrus fruits. To delay fruit ripening, produce is often stored under oxygen-depleted conditions, and ripening is subsequently controlled by introducing an oxygen-ethylene mixture. The patented compound ethephon decomposes to release ethylene upon application; it is sprayed onto rubber trees to stimulate the flow of latex from their trunks.