ABA also helps cause normal embryogenesis, formation of seed storage protiens and prevents premature germinaton or growth of many seeds and bulbs.
ABA can affect the cell in three different ways depending on the tissue involved.
Research on Commelina guard cells gives evidence for an intercellular ABA receptor. When ABA is caged and microinjected then photolysed to release ABA internally stomatal closure results. This gives evidence for an internal ABA receptor. It was previously thought that ABA signals were only transduced through increases in cytosolic calcium however recent evidence suggests that there are actually two pathways that can lead to stomatal closure in guard cells. When guard cells were grown at 10-17 degrees celcius most failed to exhibit any ABA induced free calcium although all cells closed.