Translocation Flashcards
(15 cards)
Intitail explanation for translocation
Mass flow hypothesis
Source
Where photosynthate is produced and exported
sink
Growing parts of the plant, where photosynthate is used
Explain the mass flow hypothesis
Photosynthesis produces sugars which diffuse into sieve elements of the phloem decreasing water potential
Water enters phloem via osmosis
Hydrostatic pressure increases forsing the sap towards the sink down press grad
arguments against mass flow 5
No use for sieve plates, they just impede flow
No reason for companion cells across WHOLE length of phloem
Bidirectional flow with different rates would not be possible
When phloem cells are killed translocation stops
Rate of translocation is faster than possible by a passive method
New theory to explain loading of sucrose into phloem 3
H+ ions active trans out of companion cells into sink cells
Diffuse back into companion cells via co-transport with sucrose
Sucrose diffuses into the sieve tube elements of phloem via plasmodesmata
Newer explanations for bidirectional flow
Cytoplasmic streaming
Protein filaments
Observations of ringing experiment
Bulge above ring indicating accumulation of sap
Eventual death of roots
Effect of removing a layer of bark
Removes the phloem as they are peripheral
Conclusions of ringing experiment 2
Sucrose moves source to sink
Sucrose must be moving through the phloem as removing the phloem inhibited translocation
Conclusions of aphids and tracers 3
Rate of translocation is fater than passively possible
Sugars must be in phloem
Source to sink
How do radioactive regions appear on autoradiograms
Fogged
Conclusions of autoradiography
Sap flow is bidirectional
Source to sink
how can aphids be used to analyse the phloem contents
Allow to feed
Anethetise with CO2
Cut off inserted styler
Analyse flowing sap
What observation when the styler of aphids is removed suggests that sap is under pressure
Sap flows from stylet
