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The plant hormone released during stresses such as injury, chemical exposure, drought, flooding, and infection is called ethylene. This hormone is also responsible for fruit ripening and programmed cell death called apoptosis. Ethylene induces apoptosis in response to the high concentration of auxin.

Ethylene production is observed in the growth of the seedling. When a tip of the seedling experiences any obstacle, ethylene is produced due to the stress. After ethylene production, the seedling shows horizontal growth, and this mechanism is called the triple response.

Ethylene incentive mutants are mutants that lack functional ethylene receptors. The tip of the seedlings fails to produce ethylene while facing an obstacle and does not show horizontal growth. It retards the development of the seedling.

The seedlings show horizontal growth even in the air without any obstacles, and it is found in the mutants which overproduce the ethylene.Regulatory defect of the mutants is the primary reason for this effect.These mutants are also known as ethylene overproducing mutants (eto).

The constructive triple response (ctr) mechanism is obtained by inducing the ethylene overproducing mutants into the wildlife. This restoring process turns on the permeant ethylene transduction mechanism in wildtypes.