PltSensorySysts-Chpt.40 - PLANT SENSORY SYSTEMS CHAPTER 40...

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PLANT SENSORY SYSTEMS CHAPTER 40 and 41 This chapter is equivalent to the two chapters on the nervous system and endocrine systems for animals! Plants respond much like animals to all sorts of environmental cues, but “homeostasis” is not a part of their life history. The first part of Chapter 41 is included because of the connection to flowering. Plants “sense” environmental cues such as light, gravity, touch, hydration (or lack thereof), and temperature and convey these signals by transduction to the appropriate cells (Fig. 40.4). We see this process on a macroscopic scale, but the signaling is at the cellular level. Plants respond to light – Pp 808 – 809: One needs to distinguish between photomorphogenesis and phototropism . Photomorphogenesis is discussed at the beginning of Chpt. 41 – pp 832 – 837. Personally, I find these two terms to be overlapping and the use of both to be confusing. However………. Red receptors often trigger photomorphogenesis (Fig. 40.2; 41.2) – changes in morphological growth due to light. It is true that plants go through metamorphosis much like their animal counter-parts. This is called “ competence ” and it is the internal development that allows plants to obtain competence to respond to a stimulus. This process in plants is called “ phase change ” in contrast to metamorphosis. Adults may or may not produce reproductive structures depending on a large host of environmental cues. One cue is light – Fig. 40.2. Figure 40.2 describes how the plant responds to Phytochrome (and actually, there are several different phytochrome molecules). Notice from Fig. 40.2, the plant can measure daylight length (by measuring the degredation of P fr – Fig. 41.6). This is termed “ photoperiodism .” As a result there are “long-day” and “short-day” plants. There are also “ day neutral ” - plants. Photoperiod can be manipulated artificially so that plants flower at a certain time. Causing Poinsettias to flower at the winter holiday season is a good example (Fig. 41.7). There are applications as well. For example, why doesn’t ragweed grow in Maine? Plant flowering also responds to temperature. This is called “ vernalization .” This is also called a “ temperature-dependent pathway which contrasts with the “light-dependent” pathway above. The “autonomous pathway” to flowering is independent of environmental cues – except for nutrition.
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This note was uploaded on 03/31/2008 for the course BIOL 1106 taught by Professor Georgesimmons during the Spring '08 term at Virginia Tech.

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PltSensorySysts-Chpt.40 - PLANT SENSORY SYSTEMS CHAPTER 40...

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