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The Downward Movement of Sugary Plant Fluids in Phloem
..... (12/99 Urbana IL) Some exciting findings just out show how plants move fluids long distances in their phloem DOWNWARDS in plants. ..... As with most findings, these are built upon earlier findings. ..... In this case, upon the work of Ernst Munch in the 1930's.
..... The plants have a pump! ..When sucrose is made in the leaves, it is pumped into certain cells where it accumulates at up to 100 times the level found elsewhere in the plant. ..This produces an extremely hypertonic situation, so water, of course, diffuses into these cells causing a lot of pressure that pushes the sap through the phloem to the destination or "sink" tissues. .. Here is the overall scheme for the DOWNward movement:
..... Conversely, there are several hypotheses as to how water rises UP in the xylem to the tops of tall trees, but each hypothesis does not - ahem - hold water, as it were (see transpiration). ..How this transpiration really happens can be the subject of your project.
..... The discovery group is led by Assoc. Prof. Daniel R. Bush, who is director of the interdepartmental program in Physiological and Molecular Plant Biology at Univ. of Illinois, Urbana, IL. ..Bush is also a scientist with the Photosynthesis Research Unit of the U.S. Dept. of Agriculture.
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