Q.24 Companion cells which are located close to the sieve tube serve the same function as
Companion cells, located adjacent to sieve tubes in phloem, provide metabolic support including protein synthesis and loading/unloading of sugars, a role equivalent to Strasburger cells (also called albuminous cells) in gymnosperms, making option (1) correct.
Option Analysis
Strasburger Cells (1) – Correct
Strasburger cells, or albuminous cells, are specialized parenchyma cells in gymnosperm phloem that function identically to companion cells in angiosperms. They supply sieve cells (gymnosperm equivalents of sieve tubes) with ATP, proteins, and maintenance via plasmodesmata, as sieve cells lack nuclei and ribosomes.
Bulliform Cells (2) – Incorrect
Bulliform cells, or motor cells, are large, thin-walled cells in grass leaf epidermis that regulate water loss and leaf rolling during drought by changing turgor; they have no role in phloem transport or metabolic support.
Phellogen (3) – Incorrect
Phellogen, or cork cambium, is a lateral meristem producing bark (phellem and phelloderm) for secondary growth and protection; it is unrelated to phloem conduction or cellular support functions.
Cells with Bars of Sanio (4) – Incorrect
Bars of Sanio are thickenings on sieve plates in gymnosperm sieve cells, aiding structural integrity during sap flow; they are not cells and do not perform companion cell-like metabolic roles.
Companion cells sieve tube Strasburger cells function highlights the phloem’s efficient nutrient transport in plants, where companion cells support enucleate sieve tubes just as Strasburger cells aid sieve cells in gymnosperms.
Phloem Structure and Role
In angiosperms, sieve tube elements stack end-to-end with sieve plates (pores for sap flow) but lack nuclei/ribosomes, relying on adjacent companion cells for metabolism, sugar loading via plasmodesmata, and pressure gradient maintenance. Gymnosperms use sieve cells with Strasburger (albuminous) cells performing the same support, ensuring bidirectional transport of sucrose and signaling molecules.
| Cell Type | Location | Key Function | Plant Group |
|---|---|---|---|
| Companion Cells | Next to sieve tubes | Metabolic support, phloem loading | Angiosperms |
| Strasburger Cells | Next to sieve cells | Equivalent support, ATP supply | Gymnosperms |
| Bulliform Cells | Leaf epidermis | Water regulation | Grasses |
| Phellogen | Secondary growth | Bark formation | Woody plants |
Exam and Plant Physiology Insights
This analogy is crucial for exams like NEET Botany or GATE Life Sciences, distinguishing phloem specializations from unrelated tissues. In agriculture, enhancing phloem efficiency via these cells boosts crop yield in nutrient-stressed soils like Rajasthan’s arid regions.
