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Endodermis Part Deux |
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Endodermis Part Deux |
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An Endodermal cell
seen with an Electron Microscope. It looks like a Parenchyma cell except that there are no
large Plastids. Note the Circles on the Radial Walls! |
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| Same as above but Labeled to show the location of the Casparian Strip! | |
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High Magnification view of the Casparian Strip (CS) as seen with an Electron Microscope. Note that the dense material permeates the entire cell wall and middle lamella of both cells. This is due to the presence of Suberin. The Plasmalemma is firmly attached to the CS. The black globules are in the Vacuole and are touching the Tonoplast. Locate the Cytoplasm and the Plasmalemma! |
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| In the Absence of a Casparian Strip, Solute Molecules would become equally concentrated on each side of the Endodermis. | |
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The Endodermis can exclude solute molecules if the Plasmalemma is impermeable to them. Alternatively, it can also accumulate molecules against a concentration gradient with the expenditure of ATP. Thus, it helps to create concentration gradients. Concentration gradients are important for the control of water uptake and transport, and it all starts right here at your friendly neighborhood Casparian Strip!
Potential Role of
the Endodermis in the Most of the water absorbed in the roots is pulled through the root system, the shoot system and the leaves by a negative (suction) pressure that develops from Transpiration. Tracheary Elements need thick lignified walls to prevent their collapse under this suction. However, these wall traits would limit absorption by Tracheary Elements in the Root Hair Zone. The Positive Root Pressure created by the Endodermis may solve this dilemma. Tracheary Elements in the Root Hair Zone may have thin partially lignified walls that facilitate water uptake. They do not need to be as rigid as those found in more mature regions of the root and the rest of the plant because they are not subjected to suction. *****This would be an interesting Hypothesis for a 399 project. In order to get a handle on this Tracheary elements could be isolated from different parts of the root and their wall structures could be compared! |
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Some of the most complex Secretory Trichomes we studied earlier, like Salt Secreting Trichomes have cells with Casparian Strips. Salt is actively secreted across an Endodermis-like group of cells, at the base of the trichome and the Casparian Strip blocks the possibility of apoplastic flow which could let the salt diffuse back into the leaf parenchyma.
There are many Halophytes (Salt-loving) plants in Hawaii, and in other places with saline environments. Salt secreting glands are important adaptations for plants living in such environments.
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| Ranunculus Vascular Cylinders with Bright Field and Polarized Illumination. Locate the Endodermis. | |
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| Vascular Cylinder from Corn Roots: Locate the Endodermis! | |
 Vascular Cylinder from Clintonia: Note the prominent Endodermis! |
 Cross section of a Smilax root: The Endodermis is easy to spot. |
 Epidermis, Cortex and outer part of the Smilax Root: Locate the Exodermis and Endodermis! |
 Outer part of a Smilax Root: Note the Exodermis! |
Thus, solute and solvent (water) movement are brought under the regulation of living cells. This may not sound very impressive but if it weren't for the Casparian Strip we would all be eating Algae. Furthermore, there would be no shade, no cloth, no wood and no Plant Anatomy classes!!!
Root Directory
