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Unformatted text preview: ARABIDOPSIS GENET ICS: HOR MONES AND GROWTH LIFE 37 37.1 How does plant development proceed?- Four factors are involved in regulating plant growth : Environmental cues to which a plant responds Receptors that allow a plant to sense environmental cues, such as photoreceptors , molecules that absorb light Hormones , chemical signals that mediate the effects of the environmental cues including those sensed by receptors The plant s genome , which encodes enzymes that catalyze the biochemical reactions of development 37.1.1 Several hormones and photoreceptors play roles in plant growth regulation- Hormones are regulatory compounds that act at very low concentrations at sites often distant from where they are produced. Unlike animals, which produce each hormone in a specific part of the body, plants produce hormones in many cell types. Each plant hormone plays multiple regulatory roles, affecting several different aspects of plant development-Like hormones , photoreceptors are involved in many developmental processes in plants . Unlike plant hormones , which are small molecules , plant photoreceptors are pigments ( molecules that absorb light) associated with proteins . 37.1.2 Signal transduction pathways are involved in all stages of plant development- Plants , like other organisms , make extensive use of signal transduction pathways , sequences of biochemical reactions by which a cell generates a response to a stimulus . Cell signaling in plant development involves a receptor (for a hormone or for light) and a signal transduction pathway , and concludes with a cellular response. Protein kinase cascades amplify responses to signals in plants , as they do in other organisms 37.1.3 The seed germinates and forms a growing seedling- If all developmental activity is suspended in a seed , even when conditions appear to be suitable for its growth , the seed is said to be dormant . Cells in dormant seeds do not divide, expand, or differentiate.- As the seed begins to germinate to develop into a seedlingit takes up water. The growing embryo then obtains chemical building blocksmonomersfor its development by digesting the polysaccharides , fats , and proteins stored in the seed . The embryos of some plant species secrete hormones that direct the mobilization of these reserves. Germination is completed when the radicle (embryonic root ) emerges from the seed coat. The plant is then called a seedling . 37.1.4 The plant flowers and sets fruit- Flowering the formation of reproductive organsmay be initiated when the plant reaches an appropriate age or size. Some plant species , however, flower at particular times of the year, meaning that the plant must be capable of distinguishing different times of the year. In these plants , the leaves measure the length of the night (shorter in summer, longer in winter)-Once the leaves have determined that it is time for the plant to flower , that information must be transmitted as a signal to the places where...
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This note was uploaded on 09/02/2009 for the course BIO 315H taught by Professor Payne during the Spring '08 term at University of Texas at Austin.
- Spring '08