Relationship between sieve tubes and companion cells

Sieve elements vs Companion cells - Compare and contrast table in A Level and IB Biology

relationship between sieve tubes and companion cells

Companion Cells and Sieve Tubes: Difference | Plant Tissue | Botany. Article shared by: The upcoming discussion will update you about the differences. While companion cells attached to the sieve tube elements and helps to maintain the pressure between from where the food transport to where. Sieve cells are long, conducting cells in the phloem that do not form sieve tubes. The major difference between sieve cells and sieve.

Discovery[ edit ] Sieve elements were first discovered by the forest botanist Theodor Hartig in Since this discovery, the structure and physiology of phloem tissue has been emphasized more as there has been greater focus on its specialized components such as the sieve cells.

Since then, multiple studies have been conducted on how sieve elements function in phloem in terms of working as a transport mechanism. By studying the phloem of the leaves in vivo through laser microscopy and the usage of fluorescent markers placed in both companion cells and sieve elementsthe network of companion cells with the compact sieve tubes was highlighted. The markers for sieve elements and companion cells was used to study the network and organization of phloem cells.

Sieve tube element

This allows for supply and maintenance of the plant cells and for signaling between distant organs within the plant.

Companion cells provide Sieve tube members with proteins necessary for signaling and ATP in order to help them transfer molecules between different parts of the plant. It is the companion cells that helps transport carbohydrates from outside the cells into the sieve tube elements.

This is due to the fact that sieve tube members do not have ribosomes to synthesize protein as this makes it harder to determine which active proteins are specifically related to the sieve tube elements.

Phloem Structure | BioNinja

The companion cells shown contain a nucleus which can synthesize additional protein for cell signaling. The bidirectional flow of nutrients is shown with the double arrow.

Sieve tube members and companion cells are connected through plasmodesmata. Structurally, the walls of sieve tubes tend to be dispersed with plasmodesmata grouped together and it is these areas of the tube walls and plasmodesmata that develop into sieve plates over time. Sieve tube members tend to be found largely in angiosperms.

relationship between sieve tubes and companion cells

Sieve plates contain sieve pores which can regulate the size of the openings in the plates with changes in the surroundings of the plants. Formed through these vertical connections between multiple sieve tube members, sieve tubes are directly responsible for the transport through the minimum resistance surrounding their walls. This regulation is necessary for the sieve tubes to respond to changes in the environment and conditions within the organism.

Despite these obstacles it was possible to reveal in comparative plant anatomical studies of monocots definite phylogenetic trends V. The originally scattered pits are concentrated in 'sieve areas' accumulations of pores. The diameter of a pore is around 0. Specialized sieve areas are concentrated in the final walls.

A gradual change of orientation of these final walls from very sloping to right angles occurs. The change is followed by a stepwise transition from compound to simple sieve plates.

The activity of the sieve areas in the side walls is reduced. This leads to canalizing of the flow of assimilates in longitudinal direction and the long-distance transport rates are enhanced. Phloem elements of the roots are normally organized in a more progressive and thus more efficient way than their equivalents in the shoots.

Callose is deposited in the sieve plates at regular intervals and can be detected with special reagents. Resorcin blue gives a blue, aniline blue a bright yellow staining.


The amount of callose increases with cell age, continuously reducing the diameter of the pores. Sieve elements that have lost their function are blocked by thick plugs of callose. The question, what is cause and what result remains.

relationship between sieve tubes and companion cells

Are the cells inactivated by the callose plugs or do these form as a result of the loss of function? Active sieve tubes contain huge amounts of so-called P-proteins phloem - proteins. It has often been speculated, whether they have an active part in assimilate transport. No answer has been found up until now. The sieve tube elements of angiosperms mono- and dicotsbut not those of pteridophytes and gymnosperms are associated with companion cells.

In Ginkgo and other gymnosperms their function is taken over by specialized parenchyma cells, that resemble companion cells in structure: They work out the contacts between phloem and the surrounding transfusion parenchyma and can also be found as mediators between ray parenchyma cells of the bark and mature sieve cells.

relationship between sieve tubes and companion cells

Albuminous cells participate in loading and unloading of these cells. The process has been studied in detail in Pinus. Companion cells and sieve elements are of meristematic origin, their development is similar to that of the xylem. Primary phloem develops by longitudinal division and subsequent elongation of meristematic cells. The cells do often divide unequally.