1. Source: Glucose is produced in the leaves during photosynthesis. This is the source of the sugar.
2. Phloem Loading: The glucose is actively loaded into the phloem sieve tubes, which are long, thin cells connected end-to-end. This process requires energy and involves specialized proteins that transport the glucose across the cell membrane.
3. Translocation: The sugar is then transported through the phloem by a process called translocation. This involves a pressure gradient created by the difference in osmotic pressure between the source and sink (where the sugar is needed).
4. Sink: The glucose is unloaded from the phloem at various sinks throughout the plant, such as:
* Roots: for growth and storage
* Stems: for growth and support
* Fruits: for development and seed production
* Growing buds: for new growth
5. Phloem Unloading: At the sink, the glucose is actively unloaded from the phloem sieve tubes, again requiring energy and specialized proteins.
Mechanism of Translocation:
The exact mechanism of translocation is still being debated, but the pressure-flow hypothesis is the most widely accepted theory. This hypothesis suggests that:
* High sugar concentration at the source creates a high osmotic pressure, drawing water into the sieve tubes.
* This pressure pushes the sugar solution towards the sink, where sugar is being used or stored.
* Low sugar concentration at the sink creates a lower osmotic pressure, allowing water to move out of the sieve tubes.
Factors Affecting Translocation:
* Temperature: High temperatures increase translocation rate.
* Light intensity: Light increases photosynthesis, providing more glucose for translocation.
* Nutrient availability: Adequate nutrients are essential for phloem function.
* Hormones: Plant hormones like auxin and gibberellin can regulate translocation.
In summary: Glucose is transported through the plant in the phloem, traveling from its source (leaves) to various sinks throughout the plant. This process is driven by pressure gradients created by the difference in osmotic pressure between the source and sink.
