Translocation - PP Exam 2 Flashcards
What compounds can be translocated in the phloem?
amino acids / amides / ureids, proteins, hormones, inorganic ions, and carbohydrates (w/o free aldehyde or ketone group) (non-reducing)
What are types of carbohydrates that can be translocated in the phloem?What can these carbohydrates do?
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)
Why are amino acids and amides translocated in phloem?
they are the main form of nitrogen transport in phloem, amino acid transports form of glutamic acid, amide transports form of glutamine
Why are ureids translocated in the phloem?
they transport species of nitrogen-fixing bacteria, specifically Rhizobia, through allantoic acid, allantoin, and citrulline
Are proteins synthesized in sieve cells?
NO, they are transported there through the plasmodesmata between companion cells and sieve tubes
What type of proteins can be translocated in the phloem?
STRUCTURAL PROTEINS (P-proteins involved in sealing damages sieve elements by plugging sieve plate pores) and SIGNALING PROTEINS
What types of signaling molecules (besides signaling proteins) are translocated in the phloem?
hormones like auxin, cytokinins, gibberellins, and abscisic acid
mRNA
What is the phloem tissue made up of? What may phloem tissue also include?
parenchyma cells, companion cells, and sieve elements (angiosperms) or sieve cells (gymnosperms)
may also include fibers, sclereids, and lactifers
What are lactifers?
cells containing latex, and they may be present in phloem tissue
Are sieve elements in the phloem alive or dead? How are they modified? What do their cell walls lack?
ALIVE
they are modified cells: w/o nuclei, vacuoles, cytoskeleton, Golgi, or ribosomes
their cell walls lack lignin (cell walls still thickened)
How are damaged sieve elements sealed off?
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
What is callose? What is its function?
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
How are companion cells produced? What is their purpose?
produced when a mother cell divides, producing the sieve element and a companion protein
they supply ATP and proteins to sieve elements
What are the three types of companion cells?
ordinary, transfer, and intermediary
Describe ordinary companion cells.
they are only connected through plasmodesmata to their own sieve element, they are symplastically isolated from other cells
Describe transfer companion cells?
have ingrowths at cell wall, that increase the surface area of plasma membrane, also increases the potential for solute transfer across membrane
Describe intermediary companion cells?
numerous plasmodesmata connections with other surrounding cells
How does phloem sap move?
from ‘sources’ to ‘sinks’
What is a ‘source’? List some examples
part of the plant that produces sugars in excess of its needs
a mature leaf, storage tissues as endosperms or tubers
What is a ‘sink’? List some types.
part of the plant that does not produce enough sugars to satisfy its needs
roots, fruits, immature leaves
What determines which sources supply which sinks?
proximity and vascular connections
What may cause the translocation pattern to change?
development, wounding or pruning
Explain the Pressure-Flow model.
-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
What does the Pressure-Flow model explain? Are there other models explaining this as well?
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
How many methods of phloem loading are there? What is/are they
apoplastic loading, symplastic loading w/ polymer trapping, and symplastic loading (w/o polymer trapping)
Explain how apoplastic loading works?
_____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
Explain how symplastic loading w/ polymer trapping works?
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
Explain how symplastic loading (w/o polymer trapping) works?
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.
What is allocation? List an example.
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
What is partitioning? Why is it important? Specifically in agriculture?
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
Can glucose and fructose be translocated through the phloem? Why or why not?
NO
they have a free aldehyde or ketone group, so they cannot be translocated. they must be in sucrose form (glucose + fructose)
How does a symporter work? (specifically in nitrate and sucrose transport into cells)
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
