Abscisic acid physiological roles

Hartung, W., Radin, J.W. Hendrix, D.L. (1988). Abscisic acid movement into the apoplastic solution of water-stressed cotton leaves Role of apoplastic pH. Plant Physiology, 86, 908-13. 

Carotenoid catabolic products also have a physiological role in the plant. Oxidative cleavage of carotenoids by carotenoid cleavage dioxygenases (CCDs) generates apocarotenoids [21]. Apocarotenoids serve the plant as antifungal agents or in the synthesis of flavor or aroma of flowers and fruits. A well-known downstream product of an apocarotenoid is abscisic acid (ABA), a phytohormone in plants [21]. 

Roles of Metabolites of Abscisic Acid. Nothing is known about the physiological role of PA and DPA in plants, although these two metabolites of ABA have been tested in several bioassays recently. In the cotton explant abscission assay PA had one-tenth of the activity of ABA (19). PA and DPA were equally effective in inhibiting a-amylase secretion by barley aleurone layers treated with glbberellin A3 DPA had approximately one-tenth of the activity of ABA in this system (74). The effect of PA on growth of bean embryos was negligible (75). 

On the basis of genetical and physiological studies it was concluded that plants hormones like abscisic acid and gibberelline play an important role in the regulation of dormancy and germination. They suggested molecular techniques for further investigation related to these two phenomena. 

The sesquiterpene abscisic acid is also derived from isopentenyl pyrophosphate. Abscisic acid counteracts the effects of most other plant hormones. That is, it inhibits germination, growth, budding, and leaf senescence. Physiological evidence suggests a role for abscisic acid in ion and water balance. 

The phytohormone abscisic acid (ABA) plays an important role in many physiological processes in plants. This hormone is necessary for regulation of several events during late seed development [54,70]. Furthermore, ABA is crucial for the response to environmental stresses such as desiccation, salt and cold [10,39]. 

Hoad GV (1978) Effect of water stress on abscisic acid levels in white lupin Lupinus alba L.) fruit, leaves, and phloem exudate. Planta (Berl) 142 387-390 Hsiao TC (1973) Plant responses to water stress. Annu Rev Plant Physiol 24 519-570 Jones RL (1973) Gibberellins Their physiological role. Annu Rev Plant Physiol 24 571-598... 

In a recent review Cote and Crain [5] have pointed to three phenomena which they thought particularly convenient to study the physiological role of phosphoinositides in plants. These were 1) the turgor changes in stomatal guard cells, paiticulaiiy after a treatment with abscisic acid which provokes the closure of stomata, 2) the osmotic stress in Dunaliella salina or carrot cell cultures and 3) the deflagellation of Chlamydomonas reinhardtii after exposure of the alga to acid pH, elevated temperature or ethanol. Nevertheless the rates of apparition of inositolphosphates after stimulation have been found very different in various plant tissues (from 30 sec to 30 min). 

---