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Thread: What is the role of root dehydration in sugar translocation?

  1. #1 What is the role of root dehydration in sugar translocation? 
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    A perennial plant enters a phase of energy storage in the fall. Coincidentally, this is when rainfall is lower.

    I read an article about how sucrose transport via phloem involves turgor pressure, implying that the sugars above ground make their way to the roots when the roots have lower water pressure than the above-ground portion of the plant.

    Does anyone know how important root hydration levels are in this process? I'm wondering if, in the case of a perennial weed which is not desired, you could keep its roots hydrated in the summer & fall, keeping water pressure high, preventing sugars from moving downward into the roots.

    Your thoughts? Thanks!


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    Forum Junior AndresKiani's Avatar
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    I might be wrong as is usually the case lol.

    But I believe its because the adhesion and cohesion of water molecules (the whole system, like a conveying belt) is what circulates nutrients throughout a plant. When turgor pressure is low within plant cells it allows for higher rate of nutrient and water transportation into the cell. The plant cells large vacuole is the mediator of the turgor pressure within each cell. This vacuole is not only for keeping the cell at a hypotonic form (which as you already know is preferred by plants), but it also stores nutrients. Thus, if turgor pressure is very high, this also means that the cell contains a lot of nutrients with in the vacuole, and this makes it less energetically favorable to diffuse further nutrients and water into the plant cell, thus slowing down the system.

    The whole system of turgor pressure and water molecule cohesion and adhesion is what keeps nutrients and water circulating through the plant. The sun's energy is also important in this system not only for photosynthesis, but also because it vaporizes the water molecules at the top of the exposed leaves of the plant, in doing so it pulls water molecules behind it (this is part of the cohesion). Thus, this processes pulls the water molecules against gravity upwards, and nutrients as well.


    Last edited by AndresKiani; June 20th, 2014 at 09:07 AM.
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    Forum Junior AndresKiani's Avatar
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    I only know the cellular and chemical mechanisms. I have zero botany knowledge..
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    Forum Professor Zwirko's Avatar
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    Quote Originally Posted by haugeb View Post
    Coincidentally, this is when rainfall is lower.
    What part of the world do you live in? Where I am (Scotland) the Fall (or Autumn as I like to call it) is usually the wettest time of the year.

    The sugars are not moving through a water gradient from one end of the plant to the other. Instead, sugars are thought to be loaded into sieve-tube elements which causes, in turn, water to be drawn into those elements. The positive hydrostatic pressure (turgor) that is created behind the sugar-laden sap pushes the sugars through the phloem.

    In fact, how sugars (and other molecules) are translocated around the plant is not very well understood. The current theory is a little controversial as it is unable to explain several other observations - such as bidirectional translocation.
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