Sugars & hormones: Phloem Transport
Carbohydrates: produced by photosynthesis in leaves; need to be transported to growing meristems, fruits, or root storage systems; might also be retrieved from root storage systems
Photosynthetic products (glucose) converted to sucrose for transport
Mass-flow hypothesis: sugars flow from source to sink
- phloem loading: sugars enter sieve tubes by active transport (requires energy); parenchyma & companion cells provide ATP
- because sieve cells now have higher solvent concentration, water follows from adjacent xylem into phloem by osmosis
- turgor pressure in sieve cells increases and drives fluid down the phloem
- at sink, sugars are removed from sieve cells by active transport
- lower solvent in sieve cells ? water leaves phloem back into xylem