BRAINCAKEThe Apoplast Pathway
In apoplastic loading, sucrose leaves the symplast and travels through the apoplast, the cell walls and spaces between cells, before being actively taken into the companion cells. Many herbaceous plants, including many crop plants, load in this way.
1. Sucrose made in the mesophyll cells moves through plasmodesmata to cells near the phloem.
2. It then passes out of these cells into the cell walls.
3. It diffuses through the cell walls to the companion cells.
4. It is taken up into the companion cells by active loading, using the proton-sucrose co-transport mechanism described in Phloem Loading: proton pumps use ATP to move hydrogen ions out, and the hydrogen ions diffuse back in through co-transport proteins, carrying sucrose with them.
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Key terms in this lesson
- plasmodesmata
- Fine channels through plant cell walls that connect the cytoplasm of neighbouring cells, allowing transport and communication between them.
More in Transport in Plants
- Factors Affecting Transpiration
- Root Pressure
- Translocation in the Phloem
- Phloem Loading
- The Symplast Pathway
- Phloem Unloading
- Mass Flow Hypothesis
- Pressure Flow Hypothesis
All 21 lessons in Transport in Plants · All Edexcel AS-level Biology topics