Sieve cells are specialized plant cells found in the phloem tissue, primarily in gymnosperms and lower vascular plants, responsible for transporting sugars and other organic nutrients.
Based on the provided reference: Sieve cells are long, conducting cells with narrow diameter that do not have sieve plates. They are essential components of the phloem system, facilitating the movement of organic materials throughout the plant.
Key Characteristics of Sieve Cells
Sieve cells possess distinct features that enable their function in transport:
- Structure: They are elongated cells with a relatively narrow diameter.
- Absence of Sieve Plates: Unlike sieve tube elements found in angiosperms, sieve cells do not have sieve plates. This is a defining characteristic differentiating them.
- Conducting Role: Their primary function is the conduction of sugars and other organic solutes.
- Association with Albuminous Cells: They are associated with specialized cells called albuminous cells (also known as Strasburger cells).
Function and Association
Sieve cells work in conjunction with albuminous cells. The reference states that albuminous cells help in the transportation of organic materials. This association suggests a symbiotic relationship where albuminous cells provide metabolic support to the sieve cells, which lack certain organelles necessary for maintaining their function over long distances.
The organic materials transported by sieve cells typically include:
- Sugars (primarily sucrose)
- Amino acids
- Hormones
- Some mineral ions
This transport is crucial for delivering energy and building blocks from source tissues (like leaves) to sink tissues (like roots, fruits, and growing points).
Distinguishing Sieve Cells from Sieve Tube Elements
While both types of cells are involved in phloem transport, they differ significantly:
| Feature | Sieve Cells | Sieve Tube Elements |
|---|---|---|
| Presence in | Gymnosperms, lower plants | Angiosperms |
| Shape | Long, narrow | Shorter, wider |
| Sieve Plates | Absent | Present (at ends) |
| Associated Cells | Albuminous Cells | Companion Cells |
| Ends | Tapering | Blunt (connected end-to-end) |
Understanding sieve cells is key to comprehending nutrient transport in a significant group of plants, highlighting the diversity of solutions evolved for essential physiological processes.
