Topic 15.4

Topic 15.4 - Plant Physiology Online: The Mechanical...

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Plant Physiology Online: The Mechanical Properties of Cell Walls: Studies With <i>Nitella</i> A Companion to Plant Physiology, Fourth Edition by Lincoln Taiz and Eduardo Zeiger Topics Essays Study Questions Readings Help Select Chapter: Search HOME :: CHAPTER 15 :: Topic 15.4 PREVIOUS :: NEXT Topic 15.4 The Mechanical Properties of Cell Walls: Studies With Nitella The small size of typical plant cells (20 to 100 μm) has been a serious impediment to the study of cell wall mechanical properties. To measure the extensibility of isolated cell walls from higher plants, researchers must place entire frozen and thawed organs or tissues in an extensometer , as illustrated in textbook Figures 15.26 and 15.27. Although such measurements can give qualitative answers, the extensions measured cannot be related to the growth of living cells in a quantitative way, because the applied stress is uniaxial (unidirectional), whereas the in vivo stress due to turgor pressure is multiaxial (multidirectional). The giant internodal cells of the freshwater green algae Nitella and Chara have figured prominently in classic studies on ion transport, water permeability, and cytoplasmic streaming (Hope and Walker 1975). These algae are characterized by erect, branched coenocytic (multinucleate) filaments, differentiated into nodes and internodes, each node bearing a whorl of specialized lateral internodes (Web Figure 15.4.A). Web Figure 15.4.A Filament of Nitella axillaris containing several internodes and lateral internodes with branches. (From Taiz et al. 1981.) (Click image to enlarge.) The internode cell begins as a shortened disc 20 mm long, which elongates to produce a slender cylinder about 6 cm long and 0.5 mm wide at maturity. The cell expands by diffuse growth in a predominantly longitudinal direction. Because individual internode cells are large, their cell walls can be isolated and the
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This note was uploaded on 08/28/2009 for the course BIO 430 taught by Professor Dr.cohen during the Fall '09 term at Kentucky.

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Topic 15.4 - Plant Physiology Online: The Mechanical...

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