Abstract
At maturity the companion cell of the phloem of the sycamore Acer pseudoplatanus has a large nucleus, simple plastids closely sheathed with rough endoplasmic reticulum, and numerous mitochondria. The cytoplasm contains numerous ribosomes, resulting in a very electron-opaque cytoplasm after permanganate fixation. Bodies similar to the spherosomes of Frey-Wyssling et al. (4) are collected in clusters and these also contain bodies of an unidentified nature similar to those found by Buttrose (1) in the aleurone cells of the wheat grain. The pores through the wall between the companion cell and sieve tube are complex and develop from a single plasmodesma. Eight to fifteen plasmodesmata on the companion cell side communicate individually with a cavity in the centre of the wall which is linked to the sieve tube by a single pore about twice the diameter of an individual plasmodesma. This pore is lined with material of an electron opacity equivalent to that of material bounding the sieve plate pores. The development of the cell organelles, the possible role played in the phloem tissue by the companion cell, and the function of the complex pores contained in its wall are discussed.
Full Text
The Full Text of this article is available as a PDF (1.4 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- THORNBER J. P., NORTHCOTE D. H. Changes in the chemical composition of a cambial cell during its differentiation into xylem and phloem tissue in trees. I. Main components. Biochem J. 1961 Dec;81:449–455. doi: 10.1042/bj0810449. [DOI] [PMC free article] [PubMed] [Google Scholar]