Abscisic acid is one of the phytohormones present in plants and was firstly discovered in 1963 by Frederick Addicott and his colleagues (Fursule, Kulkarni, & Agarkar, 2006). It plays an important role in regulating the physiological process especially in extreme conditions, besides plant growth and plant development.
Under non-stressful conditions, abscisic acid presents in low levels in plants cells. This is because plant cells require just a low level of abscisic acid for normal growth. In stress conditions like extreme environments, abscisic acid content increases when plants exposed to extreme environments such as water shortage, salt stress, and cold.
When there is water deficiency in plants, the concentration of abscisic acid in plants’ cells increases triggering the closure of stomata. Karp (2009) stated that “abscisic acid binds to a GPCR in plasma membrane of guard cells” (p.638). The ...view middle of the document...
Abscisic acid acts as a signal that permits the increase of xylem water potential as well as water uptake to the plants. When the roots of plant are exposed directly to the salt, abscisic acid produced stimulates ions accumulation in vacuoles of root cells to allow adaption of plants to saline conditions. For instance, ABA enhances Na+ and K+ accumulations in barley roots cell (Lerner, 1999). According to Jae-Ung and YoungSook (2001), abscisic acid promotes rapid deaggregations of cortical actin filaments and delays the formation of new actin. They also stated that actin organization is the basic in signalling pathway involved in stomata closure movement. The changes affect the normal closing of stomata responses to abscisic acid. According to Javid, Sorooshzadeh, Moradi, Sanavy and Allahdadi (2011), abscisic acid inhibits leaf expansion and limits the accumulation of Na and Cl in leaves. It also delays the deleterious effect of NaCl and improves tolerance of plants towards salinity.
In additions, abscisic acid can inhibits cell growth and cell division by changing plants into dormant state during winter. Before the winter arrives, plant will produce abscisic acid that promotes abscission of leaves and fruits as prelude to this cold season. After that, it facilitates the conversion of apical meristem into dormant bud. Occasionally, abscisic acid causes plants to form hard shield covering the bud as protection against cold winter season. At this time, plant hormones will be produced inside buds which will become fruits during the following season. When the conditions are favourable for seed growth and germination, indicating the end of dormancy, other hormones that have opposite function of abscisic will increase in contents to induce the growth of plants again. The concentration of abscisic acid will return to originally low level as in non-stressful conditions. Other role of abscisic acid is that it induces certain protein synthesis in plants which helps in healing of injury.
Generally, the concentration of abscisic acid will change from time to time in response to surrounding conditions which then further generate the ABA synthesis pathways in plants to enhance plants adaption to stress.