ABSTRACT
Plants are sessile to manage the response of severe climatic stress conditions including salinity, freezing, chilling, and drought; they have developed multifarious pathways of signalling. Isoprenoid plant hormone, abscisic acid, is a vital mediator for signalling and regulation of many biological mechanisms and pathways in plants. Different important functions and properties of ABA-mediated molecular factors highlight its role in many stress responses, such as the closure of stomata, different phases of development, dormancy of bud, and germination of seeds. While signalling of ABA has a complex system that takes part in other signalling mechanisms, the classification of its complex regulatory system is mandatory to understand the role of important regulatory genes included in ABA signalling. In this chapter, we consider two main factors of ABA signalling. Firstly, we study the pathways of stress signals, including biotic and abiotic stresses, and the response system of the ABA signalling mechanisms that transfer the pathways to downstream signals to produce tolerance against stress, stomatal regulation, and signalling of ABA factor for ubiquitination. Secondly, signalling of ABA to support in different phases of development in plants including growth of lateral roots, germination of seeds, and opening and closing of flowers. Observing various combinations of dynamics signals could improve our knowledge about various fundamental mechanisms such as the biochemical, molecular, and genetics of ABA signalling system in plants.
