Many mitochondria to produce ATP for A.T of sucrose
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How are companion cell and sieve tube cells connected?
Plasmodesmata
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What are sieve tube cells?
Long columns with holes in end walls called sieve plates
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What are they like?
Alive but lose their nuclei and other organelles and cytoplasm reduced to strands around edge of cells -large vacuole .
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What do companion cells provide sieve cells with?
Protein ATP and other nutrients
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What is a source?
Where food is produced eg leaves (source of sucrose)
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What is a sink?
Where sucrose used (need sucrose eg to make starch)- growing plant eg roots, flower
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Steps of translocation?
Sucrose actively transported into sieve tube by companion cells. Reduces Water potential in phloem so water moves into phloem from xylem by osmosis increasing hydrostatic pressure as move vol in given space
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Next steps?
Inc in HP forces water and ions down to relieve pressure (mass flow-h2o&solutes flow due to force). Sucrose moves by diffusion as in root cells is being used up so dec conc (lowers W.P so moves in). Ions AT into Xylem reducing W.P
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Next?
water moves into xylem from phloem due to dec in WP- then water and dissolved ions are pulled up xylem by tension from leaves (also mass flow)
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What are radioactive isotopes useful for? how does it work?
Tracing movement of substances in plants. C14 makes 14CO2 plant grown in it so 14C incorporated into sugars produced which can be traced as they move through plant and region correspond to where phloem is in stem
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What does this show?
As other Tissues don't blacken shows they don't carry sugars and phloem alone responsible for translocation
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Greenfly/Aphids
Aphids=mouthparts called Stylets used to penetrate Phloem tubes and feed off sugary sap. If aphids anaesthetised with CO2 and cut off Stylets remain so pure phloem sap can be collected for analysis- evidence only in T is phloem
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What ensures stylet doesn't get blocked?
Aphid enzymes
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Ringing experiment?
Section of outer layers (phloem and protective layers) removed from woody stem and stem above missing ring of tissue=swells. Samples of L analysed and is rich in sugars. Non p/sthetic tissues below wither and die and above ring grow
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What does this show?
showing interruption of flow of sugars showing phloem not xylem is tissue responsible as ring didn't extend into xylem so continuity not broken and if X was responsible then then wouldn't have happened
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