This document summarizes key aspects of translocation in the phloem. It describes the differences between sieve tube elements in angiosperms and sieve cells in gymnosperms. It also outlines the roles of companion cells, P-proteins, and callose in transport. The document discusses patterns of translocation between sources and sinks, as well as factors that affect translocation rates and the materials translocated, such as sugars, proteins, hormones, and ions. Finally, it briefly introduces the pressure-flow model of translocation driven by osmotic gradients.

1. Translocation in the Phloem

2. •

3. Sieve Elements-Cells of the Phloem
1. Sieve tube elements – Angiosperm
2. Sieve cells – Gymnosperms

5. Sieve Tube Elements Sieve cells
( Angiosperms) ( Gymnosperms)

6. Sieve tube elements and Sieve cells
Sieve Tube Elements Sieve Cells
Type of Plants Angiosperms Gymnopserms
Junction Open channels, sieve Blocked with membranes
plates
P-protein present absent
Associated cells Companion cells Albuminous cells

7. P-protein – in all dicots, many monocots, absent
in gymnosperms;
- seal off damaged sieve elements
Callose – longer solution to damaged sieve tube
Wound callose – efficient seal of damaged sieve
plates
Companion cells – transport of photosynthate
from producing cells to sieve elements;
take over some metabolic function during
differentiation of sieve elements; supply
energy

8. Specialized Companion cells
1. Ordinary companion cells – have chloroplasts
2. Transfer cells – have wall ingrowths which
increase the surface area of the plasma
membrane and enhance solute transfer
3. Intermediary cells- with numerous
plasmodesmata which connect them to
sorrounding cells

9. Patterns of Translocation
Sources –areas of supply;
include photosynthetic parts or
exporting storage organ
Sink-areas of metabolism or storage ;
nonphotosynthetic organs; ex. Roots,
tubers, developing fruits, immature leaves

10. Factors which affect Translocation:
1. Proximity
2. Development
3. Vascular connections
orthostichy- vertical row of leaves
Anastomoses – vascular interconnections,
alternative pathway in cases of interferences in
the translocation path

11. Translocated Materials
1. Water – solvent of carbohydrates
2. Nitrogen- in the form of amino acids and
amides
3. Plant hormones – auxin, gibberellins,
cytokinins, abscisic acid
4. Proteins- P-proteins ( wound sealing); protein
kinases( phosphorylation);
thioredoxin(disulfide reduction); ubiquitin(
protein turnover); chaperones(protein
folding); protease inhibitors ( against insects)

12. 5. Inorganic solutes – K, P, Mg, PO4, Cl
Reducing Sugars – not generally translocated in
the phloem : aldehyde and ketone
Nonreducing sugars - sucrose

13. Rates of Movement
1. Velocity – linera distance travelled per unit
time
2. Mass transfer rate- quantity of material
passing through a given cross sectionof
phloem per unit time
* Transport velocities in the phloem exceed rate
of diffusion over long distances

14. Mechanism of Translocation
phloem loading – movement of photosynthate
from producing cells into sieve elements
phloem unloading – from sieve elements to
sink cells
Pressure-Flow Model: by Ernst Munch
A flow of solution in the sieve elements is
driven by an osmotically generated pressure
gradient between source and sink.