In order to generate a tube system of low resistance, sieve elements lose most of their cellular components such as the nucleus, cytoskeleton, ribosomes, tonoplast etc.

Mature sieve elements contain structural phloem specific proteins (P-proteins), mitochondria, ER, and sieve elements plastids.

In plants, sieve tube cells lose their nuclei at maturity (just like our RBCs), and thus lose their chromosomal DNA, but they don't lose their mitochondria.

In eukaryotic cells Wikipedia has divided extrachromosomal DNA into three parts based on where it is seen (I guess):

  1. Mitochondrial
  2. Chloroplast
  3. Circular

Sieve tube cells have mitochondrial extrachromosomal DNA at maturity, but I'm not sure about the existence of extrachromosomal circular DNA in these circumstances.

Do sieve tube cells have any extrachromosomal circular DNA at maturity?

  • $\begingroup$ Hey, got it wrong way around! Sieve cells lose the nucleus, not the companion cells. $\endgroup$ – Polypipe Wrangler Sep 11 '20 at 6:46
  • $\begingroup$ @PolypipeWrangler Corrected! Sorry. I hadn't slept for nearly twenty-four hours when I was writing this question. $\endgroup$ – a.RR Sep 11 '20 at 7:25
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    $\begingroup$ I can't add anything because the "edit" link under my question disappeared but this question is relevant. $\endgroup$ – a.RR Sep 11 '20 at 9:15

This ref. says that the plastids and mitochondria are still intact.

Found by searching for "sieve cell development"

Neuberger, D.S., Evert, R.F. Structure and development of sieve cells in the primary phloem ofPinus resinosa . Protoplasma 87, 27–37 (1976). https://doi.org/10.1007/BF01623956


  • 1
    $\begingroup$ I can't add anything because the "edit" link under my question disappeared but this question is relevant. $\endgroup$ – a.RR Sep 11 '20 at 9:18
  • $\begingroup$ I cannot edit either. $\endgroup$ – Polypipe Wrangler Sep 11 '20 at 9:33
  • $\begingroup$ Mods should do something about it. Do you know an alive plant cell that has no nucleus and no other DNA simultaneously? $\endgroup$ – a.RR Sep 11 '20 at 9:40
  • $\begingroup$ I dont know of any, apart from developing xylem cells. $\endgroup$ – Polypipe Wrangler Sep 11 '20 at 9:46
  • $\begingroup$ You know I've seen a false/true question: An alive plant cell may have no organelles. $\endgroup$ – a.RR Sep 11 '20 at 9:53

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