Abscisic Acid and Stomatal Closure
Abscisic acid is a single compound unlike the auxins, gibberellins, and cytokinins. It was called "abscisin II" originally because it was thought to play a major role in abscission of fruits. Though ABA generally is thought to play mostly inhibitory roles, it has many promoting functions as well.
In 1963, abscisic acid was first identified and characterized by Frederick Addicott and his associates. They were studying compounds responsible for the abscission of fruits (cotton). Two compounds were isolated and called abscisin I and abscisin II. Abscisin II is presently called abscisic acid.
ABA is a naturally occurring compound in plants. It is a sesquiterpenoid (15-carbon) which is partially produced via a certain pathway (mevalonic pathway) in chloroplasts and other plastids.
Because it is sythesized partially in the chloroplasts, it makes sense that biosynthesis primarily occurs in the leaves. The production of ABA is accentuated by......
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