Hormones213 - Plant Growth Regulators - 1 Growth and...

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Plant Growth Regulators - 1 Growth and development of plants, like all organisms, is regulated by a combination of genetic factors and environment influences. Plants have receptors that sense and respond to a number of environmental cues including photoperiod, temperature, pressure and moisture changes. Plant chemical growth regulators (hormones) mediate the effects of environmental cues. Genes code for the enzymes that catalyze the chemical reactions in plant growth and development. We are accustomed to studying the sensory systems of animals and the animal responses to sensory stimuli. A difference between plant responses and animal responses is that plant responses to the environment often involve differential growth patterns rather than behavioral activities in response to positive or negative stimuli. In this section and the next we will be discussing some of the chemical plant growth regulators as well as typical plant responses to environmental cues and how those responses are internally signaled from the early embryo growth ± seed and fruit development ± seed dormancy ± mobilization for germination ± vegetative growth and development ± flowering ± senescence and death. Signal Transduction Pathways in Plants We learned in Biology 211 that hormones can function as signal molecules (or ligands) that trigger signal transduction pathways in cells. Such pathways often result in the synthesis of transcription factors that in turn promote synthesis of enzymes which facilitate chemical reactions within the cell (the response). In a similar fashion, a signal molecule may function to repress transcription. Signal transduction pathways are equally important for chemical messaging in plants as in animals and both environmental cues and hormones serve as signal stimuli. We shall examine several examples of plant growth regulation involving signal pathways in this section.
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Plant Growth Regulators - 2 Plant Growth Regulators Plant hormones, or plant growth regulators, are chemicals produced by plants that alter growth patterns and/or maintenance of the plant. They can be found in many cells and tissues, although plant hormones seem to be concentrated in meristems and buds (which are dormant shoot meristems). Growth regulators control cell activities by sending chemical signals or messages to cells to do something or to not do something, including activating the genes that code for specific enzymes or blocking gene transcription. Plant hormones inhibit as well as promote cellular activities. In contrast to animal hormones, which generally have very specific effects, the hormones identified in plants most often regulate division, elongation and differentiation of cells. Most hormones have multiple effects in plants. Plant hormones, as do animal hormones, work in very small concentrations. In most cases, the effect plant hormones have on the plant depends on the
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Hormones213 - Plant Growth Regulators - 1 Growth and...

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