Abscisic acid is a plant hormone that inhibits growth and causes dormancy. It was first thought to be responsible for abscission but is now doubted. It is produced in buds to protect them during winter and can also close stomata to preserve water.
Abscisic acid is a plant hormone responsible for dormancy and growth inhibition, among other processes in plant development. When abscisic acid was first discovered and tested, it was thought to play a role in the abscission, or shedding of the plant’s leaves or fruit. This is part of how the hormone got its name, although most scientists no longer believe the acid has that function. This hormone can also be produced at certain times by a plant under stress, which can occur in situations such as lack of water.
The first time abscisic acid was identified and described was in 1963. Scientist Frederick Addicott, along with his associates, was looking for the hormone that causes fruit abscission in cotton plants. Two different compounds were isolated, which at the time were called abscisin I and abscisin II. The latter eventually became known as abscisic acid, although its role in abscission is now considered doubtful at best. Two other groups of scientists, contemporaries of Addicott, also discovered these compounds around the same time.
One of the main roles of this acid is to suspend cell growth and division when the time comes for the plant to enter a dormant state, such as in the fall. At this time of year, the hormone is produced in the buds which will become fruit during the following year. Not only does it stunt growth in various areas of the plant, but in some cases it causes a hard outer coating to form on the bud, which protects it from harsh winter conditions. At the end of a dormant period, other hormones are produced, which work in opposition to the abscisic acid, to cause renewed plant growth.
Both types of hormones are always present to some extent in the plant, but it is their relative levels that determine a plant’s state of growth. Abscisic acid can also come into play during the growing season, as a coping mechanism for stress. Specifically, it causes tiny pores on leaves, known as stomata, to close when water is scarce. This slows down the rate at which water can escape from the leaves, thus preserving the life of the plant. Finally, this acid can also be produced by a plant in response to an injury, in which case it induces the synthesis of certain proteins that contribute to wound healing.
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