plant physiology Test 2
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In sink tissue, solute potential and water potential does what?
- Solute potential decreases
- Water potential increases
Cross walls in translocation pathway allows for what?
Allows water to move from xylem and phloem
Pressure difference is maintained by?
Photosyntheic processes and movement of water
During the day, photosynthetic materials are?
Moved from chloroplasts to cytosol
At night, compounds along with glucose and starch are formed into?
Both 1st and 2nd steps of phloem loading occurs is what cell?
Sieve loading, sugar concentrations are what?
More concentrated in sieve ellements than in mesophyll cells
Initial short distance pathway. From one cell to another via plasmodesmata
Sugars enter apoplast (cell wall and extracellular spaces) prior to ploem loading.
Pathway of phloem loading (name the cells)
Bundle sheath>Intermediary cell>sieve element
Sucrose is converted into raffinose where? What is combined with sucrose to make raffinose?
Intermediary cell. Galactose is combined with sucrose
Why is sucrose converted into raffinose in the intermediary cell?
Raffinose is too large to go backwards
Sucrose is synthesized where?
Mesophyll. Combined with glucose and fructose.
3 steps to phloem unloading
Sieve element unloading>Short distance transport>Storage and metabolism
Phloem unloading can occur in what pathways?
Symplastic and apoplastic
- In young dicot is all symplastic
- Solutes move through plasmodesmata
Unloading sieve elements and companion cells occurs in apoplast
When leaf in 25% expanded/?
Source sink occurs
When leaf is 50% expanded
Source sink is complete
An immature leaf gets its photosynthate from?
Mature leaf cells
Total amount of fixed carbons per u/t
Regulation of distributed carbon to different pathways
Differential distribution of photosynthate throughout the entire plant
Sink size x sink activity
Uptake rate of photosynthate u/t
Functions of ploem
- Long distance transport of sugars
- Transport signaling molecules (physical and chemical)
Physical signals can include?
- Turgor pressure
- Ploem loading and/or unloading
Chemical signals can include?
- Plant proteins and hormones
- mRNA and RNA
When sieve element is damaged?
The pressure causes contents to surge towards damaged site
Damage to sieve elements can be caused by?
- Winds, storm, temp.
- Pollution can cause a change in light wavelength
Protective mechanisms of the phloem
- P-proteins-short term sollution. Seals damage by plugging sieve plate pores
- Callose-long term sollution. Made in sieve plate elements and plugs off sieve plate damage
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