Vondráková Z, Krajňáková J, Fischerová L, Vágner M, Eliášová K:
Physiology and role of plant growth regulators in somatic embryogenesis.
In: Vegetative Propagation of Forest Trees, ed. Park YS, Bonga JM, Moon HK, National Institute of Forest Trees, Seoul, Korea, pp. 123-169, 2016.
Keywords: phytohormones, tissue cultures, embryo, regulation, signalling, development
Abstract: Somatic embryogenesis (SE) is the developmental process by which somatic cells, under suitable induction conditions, undergo restructuring through the embryogenic pathway to generate embryogenic cells and consequently the whole plant. Within the process of SE, a single cell or a group of cells with similar morphology and genetic background respond to external stimuli produced by the surrounding tissue, in the case of natural settings, or present in the tissue culture medium. These stimuli launch a genetic program that leads to the establishment of cell lineages with an altered gene transcription pattern, and a different morphology and developmental fate. The key substances controlling the whole process of SE are phytohormones. Generally they are characterized as natural substances with signalling ability important for connections between cells, tissues and/or organs in the plant. Their specific information depends on the chemical structure of the phytohormone and on the ability of plants to receive the signal and induce a physiological response in the target plant tissue. In the present review, we focussed on seven main groups of regulators that have a fundamental influence on different developmental stages of SE - auxins, cytokinins, abscisic acid, ethylene, jasmonic acid, polyamines and phenolic compounds. We provide an overview of current knowledge of phytohormonal regulation of embryo development including the effect of crosstalks between phytohormones and/or plant growth regulators in terms of highly coordinated interactions within phytohormones signalling pathways. We considered the main mechanism of regulation in plant/embryo development as revealed by studies from zygotic as well as somatic embryos using the modern approaches of molecular biology and advanced microscopic techniques. When possible, examples from SE of conifers will be given.