5 1China Agricultural University, Beijing, China; 2Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China
Abscisic acid Jigang Li1, Yaorong Wu2, Qi Xie2, Zhizhong Gong1 5 1China Agricultural University, Beijing, China; 2Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China Summary The classical plant hormone abscisic acid (ABA) was discovered over 50 years ago. ABA accumulates rapidly in plants in response to environmental stresses, such as drought, cold, or high salinity, and plays important roles in the adaptation to and survival of these stresses. This “stress hormone” also functions in many other processes throughout the plant life cycle, acting in embryo development and seed maturation, seed dormancy and germination, seed- ling establishment, vegetative development, root growth, stomatal movement, flowering, pathogen response, and senescence. It is transported in the vascular tissues to coordinate root and shoot development and function. Receptors for ABA have been identified as a family of soluble proteins, which upon binding ABA form coreceptor complexes with phosphoprotein phosphatase 2C (PP2C) phosphoprotein phosphatases. The resulting inhibition of activity of PP2C enzymes leads to changes in phosphorylation of protein kinases and transcription fac- tors, to mediate the multiple effects of ABA. The elucidation of ABA perception mechanisms and the core components of the signal transduction mechanisms from ABA perception to downstream gene expression has expanded our understanding of the functions of ABA. This chapter summarizes our current understanding of the key components of ABA metabolism, transport, physiological functions, signal transduction, gene expression, and proteolysis. 5.1 Discovery and functions of abscisic acid Abscisic acid (ABA), a classic plant hormone, was isolated multiple times in differ- ent studies. Researchers in the early 1950s isolated acidic compounds, referred to as β-inhibitors, from plants; they separated these compounds by paper chromatography and showed that β-inhibitors inhibit coleoptile elongation in oat.
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