Lec8Translocationnotes

Hortpurdueeduhortcourseshort301 translocation

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Unformatted text preview: nger polysaccharides are synthesized maintaining sucrose diffusion gradient – polysaccharides can’t diffuse back (they are large), but can diffuse into sieve element symplastically http://www.hort.purdue.edu/hort/courses/HORT301/ Translocation Mechanism of Phloem Translocation • Requirements – Osmotic gradient between two osmometers – Membranes that allow establishment of gradient – A low-resistance pathway (tube) between osmometers that allows flow Translocation Phloem Unloading • Phloem cell to receiver cell (sink) – (1) Sucrose that enters the apoplast can be split into glucose and fructose by a wall invertase before entering a cell from a sink tissue – (2) Sucrose can be taken up into the cell unaltered. – (3) Once in the symplast of the cell from the sink tissue, sucrose can be split into glucose and fructose by a cytoplasmic invertase Translocation Phloem Unloading • Phloem cell to receiver cell (sink) – (4) Sucrose can enter the vacuole unaltered – (5) Once in the vacuole, sucrose can be split into glucose and fructose by a vacuolar invertase, or it can remain unaltered. Translocation Phloem Unloading • Process by which translocated sugars exit from the sieve elements of sink tissues • May be symplastic or apoplastic know this also it can be active http://wps.prenhall.com/ Translocation Source-Sink Interactions • Source – Supply of photosynthate • Mature leaf • Storage organ during exporting phase of development • Sink – Non-photosynthetic organs • • • • Roots Tubers Developing fruits Immature leaves Translocation Source-Sink Interactions • Overview – At source: sugars produced sugars loaded into sieve tubes tube water moves in by osmosis causing mass flow of water & assimilates to areas of low pressure – At sink: sugar...
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This document was uploaded on 01/17/2014.

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