Abstract
Overall growth and development of a plant is regulated by complex interactions among various hormones, which is critical at different developmental stages. Some of the key aspects of plant growth include seed development, germination and plant survival under unfavorable conditions. Two of the key phytohormones regulating the associated physiological processes are gibberellins (GA) and abscisic acid (ABA). GAs participate in numerous developmental processes, including, seed development and seed germination, seedling growth, root proliferation, determination of leaf size and shape, flower induction and development, pollination and fruit expansion. Despite the association with abiotic stresses, ABA is essential for normal plant growth and development. It plays a critical role in different abiotic stresses by regulating various downstream ABA-dependent stress responses. Plants maintain a balance between GA and ABA levels constantly throughout the developmental processes at different tissues and organs, including under unfavorable environmental or physiological conditions. Here, we will review the literature on how GA and ABA control different stages of plant development, with focus on seed germination and selected abiotic stresses. The possible crosstalk of ABA and GA in specific events of the above processes will also be discussed, with emphasis on downstream stress signaling components, kinases and transcription factors (TFs). The importance of several key ABA and GA signaling intermediates will be illustrated. The knowledge gained from such studies will also help to establish a solid foundation to develop future crop improvement strategies.
Highlights
Overall growth and different developmental stages of plants are under strict regulation by several classes of plant hormones
These findings clearly indicate that plants maintain the availability and level of abscisic acid (ABA)-gibberellic acid (GA) in Germination and Abiotic-Stress hormones in different parts of the plant body at different developmental stages in an intricate and balanced manner
We described the individual roles of GA and ABA in two important aspects affecting plant development; germination and abiotic stresses
Summary
Overall growth and different developmental stages of plants are under strict regulation by several classes of plant hormones. Abiotic stresses trigger ABA biosynthesis, which mediates stress adaptive responses by activating several specific signaling cascades and regulating different physiological and growth-related processes. In crop plants improved tolerance toward various abiotic stresses has been reported by introducing or inducing expression of genes encoding key enzymes of ABA biosynthesis (Table 1). The identification and characterization of NCED genes revealed that the tissue-specific expression of these genes and the resultant modulation of endogenous ABA level at different developmental stages are responsible for the regulation of specific processes, such as seed maturation and seed germination, besides response to abiotic stresses (Lefebvre et al, 2006; MartínezAndújar et al, 2011). The induction of NCED6 inhibits seed germination by increasing the endogenous level of ABA These and similar findings have clearly established a causal role for ABA in regulating the physiological and developmental processes studied.
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