Sugar Movement In Plants Flashcards
Plant Transportation System?
Plant Transportation System
Sugar,aminoacidsand some hormones (IAA and GAs) move in Phloem (slow ~1 m/hr)
Water, some hormones (CK, ABA and GAs) and minerals move in xylem (fast ~2 m/hr in small vessels, ~50 m/hr in large vessels
Development Of Mature Phloem?
• Phloemaliveatmaturity
• Membraneisveryimportant
• Companioncellstakeoverthemetabolismtoallow more “room”
• Movement in Phloem is slow relative to xylem
How does sugar move around in plants?
- Pressure Flow Hypothesis
* Involves the loading at the source and unloading at the sink
What is Phloem Loading?
Phloem Loading • Two methods
– Symplastic movement (through plasmodesma)
– Active transport Sugar molecules are ACTIVELY transported with sugar carriers (require ATP)
What is the Pressure Flow Hypothesis?
• Step 1 Sugars are actively loaded at the source
• Step 2 Sugars in the phloem becomes more concentrated
• Step 3 Water moves from surrounding xylem vessels by osmosis (NO ENERGY EXPENDED
AT THIS POINT)
• Step 4 With water moving into the phloem the pressure increases
• Step 5 Water flows from high pressure to low pressure along the phloem column
• Step 6 At the Sink, Sugar is actively unloaded (requires energy- Active Transport)
• Step 7 Water leaves the phloem by osmosis because there is less sugar
Review
• Water moves though membranes to try to dilute solutions
• Rate of movement is based on the concentration differences between the solutions
• Cell walls stop the cells from bursting
• Osmotic potential (neg.) moves water into cells but pressure (pos.) pushes water out.
• Pressure-flow hypothesis
– At the source, actively load sugar into the phloem,
– water follows to dilute the sugar
– water pushes the sugar along the column to the sink – At the sink actively unload the sugar
– Water leaves bock to the xylem
Energy is required to load and unload the sugar, but movement is a free ride.
