Papers > Science > Mechanisms of transport in the phloem and xylem
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Mechanisms of transport in the phloem and xylem
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Mechanisms of transport in the phloem and xylem
Phloem
Carbon compounds produced by photosynthesis in the leaves are distributed throughout the plant by the phloem. ... Organic molecules such as sugars, amino acids, certain hormones, and even messenger RNAs are transported in the phloem through sieve tube elements. The major compound translocated in the phloem is the sugar sucrose. ... The products of photosynthesis can be translocated through the phloem to other parts of the plant where they are needed, such as developing leaves, roots, and fruits. ...
In contrast to xylem transport, translocation through the phloem is an energy requiring process that is dependent on the metabolic activity of the phloem cells. The movement of food through the phloem is called the pressure-flow hypothesis.
The pressure-flow hypothesis means that water containing sugars and other organic molecules flows under pressure through the phloem. The pressure is created by the difference in water potential of the phloem sap versus the relatively dilute water solutions in the nearby xylem ducts.
At their "source" - the leaves - sugars are pumped by active transport into the companion cells and sieve elements of the phloem.
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Paper Information
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Title: Mechanisms of transport in the phloem and xylem
Words: 837
Rating: None
Pages: 3.3
submitted by: cjayjay
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