Abscission

A plant will abscise a part either to discard a member that is no longer necessary, such as a leaf during autumn, or a flower following fertilisation, or for the purposes of reproduction.

Premature leaf abscission has been shown to occur in response to infestation by gall aphids.

[6] The plant cells at the abscission zone will take in a large amount of water, swell, and eventually burst, making the organ fall off.

However, the yellow color can attract aphids, so some trees turn the leaves red instead by injecting a bright pigment.

[citation needed] A variety of reactive oxygen species (ROS) are generated by plants during times of stress (biotic and abiotic), including UV light, cool temperatures, excessive light, pathogens, parasites, and high salinity.

The presence and continuous production of these ROS causes disruption in the homeostasis of the cellular components, leading to metabolic dysfunction and expression of cell wall-degrading enzymes (WDEs).

In fact, auxin, a plant hormone, and ethylene have been implicated as prominent regulators of abscission signaling.

When the plant is then exposed to ethylene, gene expression of cell wall-degrading enzymes such as cellulase and polygalacturonase are activated.