Plant cells sieve tubes

Sieve cells More primitive than sieve tube members and occur in nonflowering plants sieve cells contain clusters of pores, which are narrow and uniform in structure Translocation of sugars and other organic nutrients... 

It has also been suggested that the betalain- and anthocya-nin-producing families of this order developed from a common ancestor before the widespread occurrence of floral pigments in angiosperms (Mabry, 1976). All families of the Caryophyllales contain sieve-tube cells with proteinaceous inclusions which are not encountered in other plant families. However, because anthocyanins are known from most other groups of plants including gymnosperms and ferns, it seems likely that the ancestors of the Caryophyllales also possessed anthocyanins. 

In other experiments, internodes were cut free of the entire rest of the plant and regeneration tested in these isolated stem pieces. lAA added to the apical end of such an excised older internode increased sieve-tube regeneration over the controls (LaMotte and Jacobs 1963, Thompson and Jacobs 1966). The dose-response curve of apically applied lAA, as it affected both tracheary and sieve cells, is shown in Fig. 4.9 with no externally added lAA, a small number of sieve-tube cells but no tracheary cells regenerated as the lAA level was increased, more vascular cells of both types regenerated (Thompson and Jacobs... 

Plants intact except for the transverse wound regenerated numbers of vascular cells equivalent to those formed by about 0.05% lAA added to the isolated internode (asterisks in Fig. 4.9). Hence, 0.05% lAA in lanolin exactly replaced the root system and the rest of the shoot system in their effects on the regeneration of both sieve tubes and tracheary cells. At any one lAA level, more sieve cells than tracheary cells regenerated. 

Two complex tissues, the xylem and phloem, provide the conducting network or "circulatory system" of plants. In the xylem or woody tissue, most of the cells are dead and the thick-walled tubes (tracheids) serve to transport water and dissolved minerals from the roots to the stems and leaves. The phloem cells provide the principal means of downward conduction of foods from the leaves. Phloem cells are joined end to end by sieve plates, so-called because they are perforated by numerous minute pores through which cytoplasm of adjoining sieve cells appears to be connected by strands 5-9 pm in diameter.154 Mature sieve cells have no nuclei, but each sieve cell is paired with a nucleated "companion" cell. 

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