Direct Effect Of Aba example essay topic

Abscisic Acid and Stomatal ClosureAbscisic acid is a single compound unlike the auxin's, , and. It was called 'abscising 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, acid was first identified and characterized by Frederick Addi cott and his associates. They were studying compounds responsible for the abscission of fruits (cotton). Two compounds were isolated and called abscising I and abscising II.

Abscising II is presently called acid. ABA is a naturally occurring compound in plants. It is a (15-carbon) which is partially produced via a certain pathway (pathway) in chloroplasts and other plastids. Because it is synthesized partially in the chloroplasts, it makes sense that biosynthesis primarily occurs in the leaves. The production of ABA is accentuated by stresses such as water loss and freezing temperatures. It is believed that biosynthesis occurs indirectly through the production of carotenoids.

Carotenoids are pigments produced by the chloroplast which have 40 carbons. Breakdown of these carotenoids occurs in a complex mechanism which produces ABA. The transport of ABA can occur in both xylem and phloem tissues. It can also be translocate d through cells.

The movement of acid in plants does not exhibit polarity like auxin's. 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 increase in ABA synthesis). o Inhibits shoot growth but will not have as much affect on roots or may even promote growth of roots. o Induces seeds to synthesize storage proteins. o Has some effect on induction and maintenance of dormancy. (This information taken from web) Stomatal Closure Addition of ABA to the growth medium (a mixture of vermiculite and peat moss) causes the closure of the stoma tes within 3 h and an increase in the Pos of the protoplasts of the aba 1 plants to 50 mm's-1. o Arrival of ABA in the leaves appears to signal stomatal closure as well as a change in the Pos of the plasma membranes. o We hypothesize that under non-stress conditions ABA is required to maintain a population of actively functioning at the plasma membrane. o It is not clear whether this is a direct effect of ABA or the indirect effect of reducing the transpiration stream. When the transpiration stream is reduced, this eliminates primarily the apo plastic flow of water. o When the stoma tes are closed, a higher trans cellular flow may be required. We have also reduced the transpiration stream by growing the plants under high humidity (85% RH) and this also causes the Pos of the leaf protoplasts to increase significantly.

(This information taken from web).