Abscisic acid is a plant hormone synthesized mainly in the leaves, but also in small concentration in the stem and hood, it acts in the inhibition of stem and root growth, in the breaking of seed dormancy and in the closing of the stomata when there is no water at plants.
During favorable periods, the plant's buds are in intense activity, constantly dividing their cells and promoting plant growth, while in unfavorable periods the buds remain at rest, which can also influence the transport of photosynthesized products from the leaves towards the seeds in development.
Ethylene, on the other hand, is a gas produced in small amounts in various organs of a vegetable (in leaf nodules and fruit), in response to stress, especially in tissues subjected to senescence (natural aging process), in which it exerts a hormone effect, being the only hydrocarbon with evident implication on plants.
This substance helps in the germination of seeds, ripening of fruits and abscission (fall) of the leaves of certain plants.
By Krukemberghe Fonseca
Graduated in Biology
Source: Brazil School - https://brasilescola.uol.com.br/biologia/acido-abscissico-etileno.htm