translocation

definition

• the transport of manufactured food substances (sucrose and amino acids) in plants from the leaves to the rest of the plant

• bi-directional

  • can move up/down phloem tissue

loading of sucrose

• sugars manufactured during photosynthesis may be converted into sucrose

• sucrose (sol. form) movies form mesophyll cells into phloem tissue with the help of companion cells through active transport

unloading of sucrose

• sucrose exits via diffusion down its concentration gradient into cells that are sucrose-hungry

• pressure is reduced at the ‘sink’ and further promote mass flow of more sucrose solution form the ‘source’

process

1. water absorption for nearby cells increases hydrostatic pressure in mesophyll cells

2. PHLOEM LOADING: transfer of organic food form mesophyll cells to sieve tube

3. water entry form xylem to sieve elements by osmosis

4. Hydrostatic pressure difference drives solute movement from sieve tube to sink

5. PHLOEM UNLOADING: transfer of organic food from sieve tube to sink

6. water moves back to xylem vessels by osmosis and transpiration pulls up water