Abscisic acid (ABA) is a plant hormone that helps regulate various processes in plants. It is involved in seed and bud dormancy, the control of organ size, and the closure of stomata (tiny openings on the surface of leaves). It is especially important for plants in responding to environmental stresses such as drought, soil salinity, cold temperatures, freezing, heat stress, and heavy metal ion tolerance.
The discovery of abscisic acid dates back to the 1940s when researchers found a correlation between the rest period of potato tubers and the presence of an acidic growth inhibitor. In 1963, abscisic acid was identified and characterized as a plant hormone by scientists studying compounds that cause shedding of cotton fruits. It was named abscisin II and later renamed abscisic acid (ABA).
In plants, ABA plays a crucial role in various functions. It helps plants respond to environmental stress and pathogens. It is produced in response to decreased soil water potential and other stressful conditions. ABA regulates stomatal closure, reducing water loss from leaves during times of low water availability. It also inhibits seed germination and promotes seed dormancy. ABA is synthesized in almost all plant tissues and can be rapidly translocated from leaves to roots.
The biosynthesis of ABA in plants involves a series of enzymatic reactions starting from the precursor zeaxanthin. ABA can be inactivated through catabolism or conjugation with glucose. Mutations in genes involved in ABA biosynthesis or sensitivity can lead to altered plant phenotypes, such as changes in seed dormancy, germination, and stomatal regulation.
ABA also has effects on fruit ripening, photosynthesis, and root growth. It plays a role in plant antiviral immunity and has been found to be present in animals, including humans. However, the biosynthesis and biological role of ABA in animals are still poorly understood.
Measuring the concentration of ABA in plant tissues can be done using various methods, such as HPLC and ELISA. Recent advancements have also allowed for real-time measurement of intracellular ABA concentrations in vivo.
In summary, abscisic acid is a plant hormone that helps plants cope with stress and regulate various developmental processes. It is involved in seed dormancy, stomatal closure, and responses to environmental stresses. Its biosynthesis and effects are complex and play a crucial role in plant survival and adaptation.