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16.4.3.4: Ethylene

Ethylene is a plant hormone that differs from other plant hormones in being a gas.

It has the molecular structure:

H2C=CH2

As they approach maturity, many fruits (e.g., apples, oranges, avocados) release ethylene. Ethylene then promotes the ripening of the fruit. Commercial fruit growers can buy equipment to generate ethylene so that their harvest ripens quickly and uniformly.

The presence of ethylene is detected by transmembrane receptors in the endoplasmic reticulum (ER) of the cells. Binding of ethylene to these receptors unleashes a signaling cascade that leads to activation of transcription factors and the turning on of gene transcription.

The ill-fated FlavrSavr tomato contains an antisense transgene that interferes with the synthesis of ethylene and hence slows ripening.

Plant functions affected by Ethylene

Ethylene also affects many other plant functions such as:

  • abscission of leaves, fruits, and flower petals
  • drooping of leaves
  • sprouting of potato buds
  • seed germination
  • stem elongation in rice (by promoting the breakdown of abscisic acid (ABA) and thus relieving ABA's inhibition of gibberellic acid)
  • flower formation in some species

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