Which phloem element closely associates with the sieve tube elements?
GeneralClass 12AllAnswered 27 Mar 2026
Answer
Companion cells
Mechanistic Insight: Companion cells are specialized parenchymatous cells connected to sieve tube elements via plasmodesmata (cytoplasmic bridges). Since mature sieve tubes lack nuclei, companion cells:
- Control sieve tube metabolism
- Maintain pressure gradients for translocation
- Regulate loading/unloading of photoassimilates (sucrose)
Evolutionary Note: This association is unique to angiosperms. Gymnosperms have albuminous cells instead.
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