Translocation - PP Exam 2

Question 1

What compounds can be translocated in the phloem?

Answer 1

amino acids / amides / ureids, proteins, hormones, inorganic ions, and carbohydrates (w/o free aldehyde or ketone group) (non-reducing)

Question 2

What are types of carbohydrates that can be translocated in the phloem?What can these carbohydrates do?

Answer 2

sucrose, raffinose, stachyose, and verbascose

they add galactose residues, increasing the size of the sugars (sucrose is fructose + glucose, then each following enzyme adds a galactose group to sucrose base)

Question 3

Why are amino acids and amides translocated in phloem?

Answer 3

they are the main form of nitrogen transport in phloem, amino acid transports form of glutamic acid, amide transports form of glutamine

Question 4

Why are ureids translocated in the phloem?

Answer 4

they transport species of nitrogen-fixing bacteria, specifically Rhizobia, through allantoic acid, allantoin, and citrulline

Question 5

Are proteins synthesized in sieve cells?

Answer 5

NO, they are transported there through the plasmodesmata between companion cells and sieve tubes

Question 6

What type of proteins can be translocated in the phloem?

Answer 6

STRUCTURAL PROTEINS (P-proteins involved in sealing damages sieve elements by plugging sieve plate pores) and SIGNALING PROTEINS

Question 7

What types of signaling molecules (besides signaling proteins) are translocated in the phloem?

Answer 7

hormones like auxin, cytokinins, gibberellins, and abscisic acid

mRNA

Question 8

What is the phloem tissue made up of? What may phloem tissue also include?

Answer 8

parenchyma cells, companion cells, and sieve elements (angiosperms) or sieve cells (gymnosperms)

may also include fibers, sclereids, and lactifers

Question 9

What are lactifers?

Answer 9

cells containing latex, and they may be present in phloem tissue

Question 10

Are sieve elements in the phloem alive or dead? How are they modified? What do their cell walls lack?

Answer 10

ALIVE

they are modified cells: w/o nuclei, vacuoles, cytoskeleton, Golgi, or ribosomes

their cell walls lack lignin (cell walls still thickened)

Question 11

How are damaged sieve elements sealed off?

Answer 11

P-proteins in angiosperms seal off damaged sieve elements by plugging sieve plate pores, prevents loss of of sap temporarily

sealed by callose that gets deposited in between cell membrane and cell wall

Question 12

What is callose? What is its function?

Answer 12

Callose is a glucan (polymer of glucose)

it is synthesized in sieve elements on the plasma membrane and gets deposited between cell membrane and cell wall, sealing off damaged sieve elements

Question 13

How are companion cells produced? What is their purpose?

Answer 13

produced when a mother cell divides, producing the sieve element and a companion protein

they supply ATP and proteins to sieve elements

Question 14

What are the three types of companion cells?

Answer 14

ordinary, transfer, and intermediary

Question 15

Describe ordinary companion cells.

Answer 15

they are only connected through plasmodesmata to their own sieve element, they are symplastically isolated from other cells

Question 16

Describe transfer companion cells?

Answer 16

have ingrowths at cell wall, that increase the surface area of plasma membrane, also increases the potential for solute transfer across membrane

Question 17

Describe intermediary companion cells?

Answer 17

numerous plasmodesmata connections with other surrounding cells

Question 18

How does phloem sap move?

Answer 18

from ‘sources’ to ‘sinks’

Question 19

What is a ‘source’? List some examples

Answer 19

part of the plant that produces sugars in excess of its needs

a mature leaf, storage tissues as endosperms or tubers

Question 20

What is a ‘sink’? List some types.

Answer 20

part of the plant that does not produce enough sugars to satisfy its needs

roots, fruits, immature leaves

Question 21

What determines which sources supply which sinks?

Answer 21

proximity and vascular connections

Question 22

What may cause the translocation pattern to change?

Answer 22

development, wounding or pruning

Question 23

Explain the Pressure-Flow model.

Answer 23

-the flow of sap movement driven by a pressure gradient
-this gradient is generated by phloem loading at the source and phloem unloading at the sink
-this difference in pressure at the source and the sink causes the flow of phloem sap
-pressure cause by water coming into the sieve elements from nearby xylem vessel elements
-water moves by a difference in pressure, not from higher to lower water potential
-sap moves passively, only using energy indirectly for the active transport of solutes (sucrose) at source and sink

Question 24

What does the Pressure-Flow model explain? Are there other models explaining this as well?

Answer 24

it explains how sap moves through the phloem, because diffusion is too slow to explain the measured rate of sap mvmt

YES, there are other models explaining sap mvmt

Question 25

How many methods of phloem loading are there? What is/are they

Answer 25

apoplastic loading, symplastic loading w/ polymer trapping, and symplastic loading (w/o polymer trapping)

Question 26

Explain how apoplastic loading works?

Answer 26

_____finish and elaborate on this card_______

molecules in the sap get out of cells into apoplast

sucrose actively transported into companion cells by a symporter

Question 27

Explain how symplastic loading w/ polymer trapping works?

Answer 27

sucrose synthesized in mesophyll cells, goes through the symplast connected by plasmodesmata so it doesn’t have to cross the plasma membrane of any plant cells

however, this loading method does not explain why sucrose moves from companion cells to sieve elements and not backwards

explained by polymer trapping, where there is an enzyme in the companion cell that adds galactose group(s) to the sucrose, increasing its size, so it cannot go backwards, it can only move through the plasmodesmata to sieve elements

Question 28

Explain how symplastic loading (w/o polymer trapping) works?

Answer 28

it works the same as normal symplastic loading w/ polymer trapping

sucrose synthesized in mesophyll cells, goes through the symplast connected by plasmodesmata so it doesn’t have to cross the plasma membrane of any plant cells

the difference is this one does not have polymer trapping as an explanation, the reason why the sucrose moves from companion cells to sieve elements and not backward is unknown.

Question 29

What is allocation? List an example.

Answer 29

the distribution of the carbon into different metabolic pathways at the source

the triose-P (triosephosphates) produced in Calvin cycle can be used to synthesize starch or sucrose, or it can be used in glycolysis for synthesis of ATP

Question 30

What is partitioning? Why is it important? Specifically in agriculture?

Answer 30

partitioning = distribution of transported sugars to different parts of the plant, to different sinks

why? = important because it determines the pattern of plant growth and the crop yield

important in agriculture because we can determine the parts of the plant that get the energy and grow, so if we were to cut them off, then this would allow for the parts of the plant related to growth to get the sugars and make a stronger plant

important to note we do not know how to modify partitioning, so we cannot do this

Question 31

Can glucose and fructose be translocated through the phloem? Why or why not?

Answer 31

NO

they have a free aldehyde or ketone group, so they cannot be translocated. they must be in sucrose form (glucose + fructose)

Question 32

How does a symporter work? (specifically in nitrate and sucrose transport into cells)

Answer 32

The hydrogen ions are pumped out of the cell by the proton pump, then the symporter allows 2 hydrogen ions back into the cell and allows the molecule (nitrate or sucrose) in as well

the hydrogen being allowed back into the cell releases energy, allowing the molecule of nitrate or sucrose in as well