Abscisic Acid and Stomatal Closure :: essays research papers

Abscisic Acid and Stomatal ClosureAbscisic acid is a single compound unlike the auxins, gibberellins, and cytokinins. It was called "abscisin II" originally because it was thought to put to work a major role in cutting off of fruits. Though ABA chiefly 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 course occurring compound in plants. It is a sesquiterpenoid (15-carbon) which is partially produced via a certain alley (mevalonic pathway) in chloroplasts and other plastids. Because it is sythesized partially in the chloroplasts, it makes sense that biosynthesis in the beginning occurs in the leaves. The production of ABA is accentuated by stresses such as water issue and freezing temperatures.It is believed that biosynthesis occurs indirectly through the production of carotenoids. Carotenoids are pigments produced by the chloroplast which waste 40 carbons. Breakdown of these carotenoids occurs in a complex appliance which produces ABA. The transport of ABA tolerate occur in both xylem and phloem tissues. It can also be translocated through paranchyma cells. The movement of abscisic acid in plants does not exhibit polarity like auxins. ABA is capable of moving both up and down the stem.The various roles of ABA are     Stimulates the closure of stomata (water stress brings about an development in ABA synthesis).      Inhibits shoot growth but will not have as much affect on roots or may even promote growth of roots.      Induces seeds to synthesize storage proteins.      Has some progeny on induction and maintanance of dormancy. ( This information taken from http//www.plant-hormones.info/abscisicacid.htm)Stomatal Closure      amplification of ABA to the growth medium (a mixture of vermiculite and peat moss) causes the closure of the stomates within 3 h and an increase in the Pos of the protoplasts of the aba1 plants to 50 mm s-1.      Arrival of ABA in the leaves appears to designate stomatal closure as well as a depart in the Pos of the plasma membranes.     We hypothesize that under non-stress conditions ABA is required to maintain a population of actively functioning aquaporins at the plasma membrane.