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Plant physio translocation in the phloem
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Plant physio translocation in the phloem



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  • 1. Translocation in the Phloem
  • 2.
  • 3. Sieve Elements-Cells of the Phloem1. Sieve tube elements – Angiosperm2. Sieve cells – Gymnosperms
  • 4. Sieve Tube Elements Sieve cells( Angiosperms) ( Gymnosperms)
  • 5. Sieve tube elements and Sieve cells Sieve Tube Elements Sieve CellsType of Plants Angiosperms GymnopsermsJunction Open channels, sieve Blocked with membranes platesP-protein present absentAssociated cells Companion cells Albuminous cells
  • 6. P-protein – in all dicots, many monocots, absent in gymnosperms; - seal off damaged sieve elementsCallose – longer solution to damaged sieve tubeWound callose – efficient seal of damaged sieve platesCompanion cells – transport of photosynthate from producing cells to sieve elements; take over some metabolic function during differentiation of sieve elements; supply energy
  • 7. Specialized Companion cells1. Ordinary companion cells – have chloroplasts2. Transfer cells – have wall ingrowths which increase the surface area of the plasma membrane and enhance solute transfer3. Intermediary cells- with numerous plasmodesmata which connect them to sorrounding cells
  • 8. Patterns of TranslocationSources –areas of supply; include photosynthetic parts or exporting storage organSink-areas of metabolism or storage ; nonphotosynthetic organs; ex. Roots,tubers, developing fruits, immature leaves
  • 9. Factors which affect Translocation:1. Proximity2. Development3. Vascular connections orthostichy- vertical row of leavesAnastomoses – vascular interconnections,alternative pathway in cases of interferences inthe translocation path
  • 10. Translocated Materials1. Water – solvent of carbohydrates2. Nitrogen- in the form of amino acids and amides3. Plant hormones – auxin, gibberellins, cytokinins, abscisic acid4. Proteins- P-proteins ( wound sealing); protein kinases( phosphorylation); thioredoxin(disulfide reduction); ubiquitin( protein turnover); chaperones(protein folding); protease inhibitors ( against insects)
  • 11. 5. Inorganic solutes – K, P, Mg, PO4, ClReducing Sugars – not generally translocated inthe phloem : aldehyde and ketoneNonreducing sugars - sucrose
  • 12. Rates of Movement1. Velocity – linera distance travelled per unit time2. Mass transfer rate- quantity of material passing through a given cross sectionof phloem per unit time* Transport velocities in the phloem exceed rateof diffusion over long distances
  • 13. Mechanism of Translocationphloem loading – movement of photosynthate from producing cells into sieve elements phloem unloading – from sieve elements to sink cellsPressure-Flow Model: by Ernst MunchA flow of solution in the sieve elements isdriven by an osmotically generated pressuregradient between source and sink.