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Translocation phloem
plant physiology book- 2nd edition
| Question | Answer |
|---|---|
| Plants evolved long distance transport that allowed the shoot and root efficient exchange of the products of | absorption and assimilation |
| the primary phloem is ____. Both the primary phloem and the primary xylem is surrounded by a ____ ____ of thick walled _____ cells which isolates the___ tissue from the ____ tissue | Toward the outside of the stem, bundle sheath, sclerenchyma cells, vascular tissue, ground tissue |
| the cells of the phloem that conduct sugars and other organic materials throughout the plant are called ____ which include the highly differentiated ___ ___ ___ (angiosperms). These are the only ones that are directly involved in ... | sieve elements, sieve tube elements, translocation |
| In vascular tissue of leaves, the __ ___ surrounds the ___ ___ all the way to their ends, isolating the veins from the ___ ___ of the leaf | bundle sheath, small veins, intercellular space |
| Explain the labeling study that show that sugar is translocated in phloem sieve elements | Marcello Malpighi removed a ring of bark around a tree ( girdling) - effect didn't affect transpiration (xylem) - sugar transport was blocked and accumulated above the girdle bark below girdle dies and bark above girdle is swollen but healthy |
| How did they determine sugar translocation in the old days? | Autoradiograph, either supply radioactively labeled CO2 to mature leaf in plant chamber or inject solution of radioactive sucrose into leaf interior, then expose to film and see where it went |
| If you look at the cross section of a tree ( the tree rings) from inner to outer what would you see? | Pith, xylem, vascular cambium, phloem |
| Sieve elements lose their __ and ___ during development. In mature cells they also lack ___, ___, _____, and ___ The organelles that are retained are | nuclei and tonoplast (vacuolar membrane) - golgi bodies, microfilaments, microbtubles, and ribosomes - modified mitochondria, plastid, and smooth ER |
| Sieve elements are characterized by ___ ___, portions of the cell wall where pores interconnect the conducting cells. (how big? ) | sieve areas, 1um- 15um |
| individual cells are joined together to form a longitudinal series called a ____. They are under very ____ internal ___ pressure. When a sieve tube is cut or punctured, .... | sieve tube, high, turgor, - the release of pressure causes contents to surge toward the cut which causes plants to lose a lot of their sugar rich phloem sap sap= fluid contents of plant cells |
| phloem protein is known as ___. Thought to be made in the ____ and transported to ____ through plasmodesmata. Functions to ____ | p protein, companion cell, sieve elements - seal damaged sieve elements by plugging up the sieve plate pores, prevent further loss of sap |
| long term solution of for damages is.. can be analyzed with ___ ___ stain. It's synthesized in.... and is deposited between ... | callose in the sieve pores, aniline blue stain, the plasma membrane, the plasma membrane and the cell wall |
| Callose synthase is arranged ____ in plasma membrane with substrates on the ____ side and product deposited on the ____ side | vectorially, cytoplasmic, wall |
| How are the sieve tube element and companion cell formed? what do they have? | division of a single mother cell, numerous intercellular connections- plasmodesmata |
| There are 3 different types of companion cells in the minor veins of mature leaves... All 3 have dense ____ and abundant ____ | 1. ordinary 2. transfer 3. intermediary cytoplasm, mitochondria |
| Ordinary companion cells have... | chloroplasts, well developed thylakoids, and a cell wall with a smooth inner surface - this type of companion cell have few plasmodesmata connecting it to other cells except to its own sieve element |
| Transfer companion cell is like ordinary companion cell except... what does this feature doe? | it develops fingerlike wall ingrowths on cell walls that face away from the sieve element. - increases surface area of plasma membrane, increasing potential for solute transfer across the membrane |
| ordinary companion cell and transfer cell are thought to... | be for taking p solutes from apoplast or cell wall space because of structure features (lack of plasmodesmata and wall ingrowths in transfer cells) |
| intermediary cell is well suited for... because... but they also have.. | taking up solutes via. cytoplasmic connections, they have lots of plasmodesmata connecting them to bundle sheath cells - small vacuoles, poorly developed thylakoids, lack of starch gains in chloroplast |
| the plasmodesmata on the intermediary cell are.. | branched, longer and more narrow |
| A molecule such as sucrose that is produced endogenously by the metabolism of the plant (photosynthesis) is called... | assimilate |
| Where do these transport assimilates? - upper mature leaves - young immature leaves - intermediate leaves growth reproduction source leaves interference with translocation pathway | upper mature leaves- growing shoot tip young immature leaves- root system intermediate leaves- both growth- root and shoot reproduction- fruit source leaves prefer supplying sink to direct vascular connection interference causes alter pattern |
| orthostichy | vertical row of leaves- leaf is connected via vascular system to other leaves directly above or below |
| anastomoses ex: | in absence of direct connection between source and sink, vascular interconnections can provide alternative pathway - pruning= cross transfer of assimilates to young leaves on pruned side - upper leaves can transfer to root if lower leaves are removed |
| What is the most abundant substance transported in the phloem | water |
| What concentration of sucrose is in phloem? | 0.3- 0.9 M |
| How is auxin transported? | Xylem and in polar transport pathway |
| What is no in the phloem | nitrate, calcium, sulfur, and iron |
| callose synthase requirers the presence of... | calcium |
| What are reducing sugars? | glucose and fructose - contain an exposed aldehyde or ketone group |
| The rate of movement can be expressed as: | velocity- distance traveled/ time mass transfer rate- how much passes through a given cross section/time |
| How do you measure rate of movement of phloem? | radioactive tracers: C11 or C14 - pulse labeling, and arrival of label at sink tissue is monitored with a detector |
| during the day, ___ ___ is transferred from chloroplast to cytosol, at night ___ is converted | triose phosphate, glucose |
| short distance transport | what I am trying to figure out- covers 2-3 cell diameters |
| sieve element loading is when | sugars are transported into the sieve elements and companion cells where they become more concentrated than the mesophyll |
| long distance transport | translocation through vascular system to sink |
| If phloem loading is partially apoplectic we have 3 basic predictions | 1. transport sugars should be found in the apoplast 2. transport sugars is supplied exogenously to apoplast- should be accumulated by sieve elements and companion cells 3. inhibition of sugar uptake from apoplast should inhibit export from leaf |
| PCMB ( p- chloromercuribenzenesulfonic acid) what does it do? | reagent that inhibits transport of sucrose across PM but does not enter symplast- it inhibits uptake of sucrose from apoplast when sugar is suppled exogenously - also inhibits export of sucrose synthesized from CO2 in mesophyll |
| sucrose cleaving enzyme | invertase |
| You can measure sugar concentration in SE/CC vs mesophyll by measuring... | solute potential using plasmolysis and light or electron microscopy |
| in the apoplectic pathway, sieve element loading uses a | sucrose H+ symport |
| ATP can be coupled to the movements of solutes across membranes in at least 2 ways | 1. primary active transport- same membrane breaks down ATP- proton pump 2. Secondary transport- solute moves against chemical potential gradient, driven indirectly by proton gradient established by primary active transport ATPase |
| the expression of SUC2 transporter begins in the __ and proceeds to the __ in developing leaves during a sink to source transition, the same pattern shown by assimilate export capacity | tip, base |
| SUC2 is in the plasma membrane of the __ ___ and not the __ __ | sieve element, companion cell |
| levels of SUT1 ____ and ____ are lower after 15 hours of darkness than after being in the light | mRNA and protein |
| efflux is enhanced by the presence of certain substances in the apoplast- could coordinate nutrient supply, increased translocation to sinks, and enhanced sink growth | potassium |
| phloem loading appears to be symplastic in plants with intermediary cells, why do they think so? | fluorescent dyes that are mobile in symplast but can't cross membranes can be microinjected into plant cells, they can move from mesophyll to minor veins- from intermediary cells to bundle sheath and mesophyll cells- movement into sieve elements not shown |
| what is the most compelling evidence for symplastic pathway? | loading of endogenous sugars is insensitive to PCMB in plants like coleus which shows they don't pass through apoplast on their way to sieve elements |
| polymer trapping model- Robert Turgeon | sucrose synthesized in the mesophyll diffuses from the bundle sheath into the intermediary cell through plasmodesmata, Raffinose and stachyose are are in the intermediary cells- thus maintaining the diffusion gradient of sucrose |
| Why is the polymer trapping model one possibility? | they can't diffuse back because they are too large... so concentration of transport sugar rises in the intermediary cells and sieve elements |
| What 3 predictions does the polymer trapping model make? | 1. sucrose should be more [ ] in mesophyll vs. intermediary cells 2. enzymes for raffinose and stachyose synthesis should be in intermediary cells 3. PD linking the bundle sheath and intermediary cells should exclude molecules larger than sucrose |
| What supports the polymer trapping model? | numerous biochemical and immunological studies have localized all the enzymes required to synthesize starchyose from sucrose in intermediary cells of cucurbits- although mesophyll cells probably also express these enzymes |
| Alternative to polymer trapping model- Yuri Gamalei and Aart van Bel | most stachyose is synthesized in mesophyll cells and stachyose is loaded into ER that extends from mesophyll into the intermediary cells across plasmodesmata |
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sunying12
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