Siebelemente. Kernlose Spezialisten fuer den Stofftransport in Pflanzen

1990

5 Abb., 25 Lit. Ang.

Unselbständiges Werk

1451

200033404

Sieve elements are plant cells specialized for long-distance transport and one of the prerequisites for the succesful evolution of higher land plants. Their joining to long files via specifically wide pores in their end walls and their peculiar differentiation involving the loss of major cytoplasmic contents make them a symplastic conduit for the rapid distribution of assimilates. The translocating sieve element is enucleate and evacuolate, but delimited against the apoplast by the plasma membrane controlling import and export of substances. In the seed plants, sieve elements are intimately connected to specialized parenchyma cells (companion cells or Strasburger cells) which help to sustain life and transport functions of their enucleate partner and share their fate when sieve elements cease to function.