Sieve tubes

Sieve tubes , lattice tubes , sieve vessels ( lat. Tuboli cribrosi ) - conductive sugar, plastic nutrients and elements in the bodies of higher plants , are developed mainly in the bast part of the vascular fiber bundle. Their main function is the transportation of carbohydrates - for example, from leaves to fruits and roots. They were discovered and named by the German biologist and forest explorer Theodor Hartig in 1837 .

The sieve tubes are single-row cords of elongated cells , thick and of various colors; their end walls are sieve plates bearing sieve fields with numerous perforations that are lined with callose from the inside. Simple plates are usually horizontal and contain one sieve field (typical examples are pumpkin and ash ), while the complex ones are inclined and have several sieve fields (such plants include linden , grapes , passionflower , rice ). Each segment of the sieve tube is adjacent to a strand of narrow accompanying cells that are physiologically associated with them ^[1] . With their development, the tonoplasts in the cells are gradually destroyed, causing a mixing of the cytoplasm with cell juice; degeneration of the organelles and cell nucleus occurs . Due to the significant amount of cytoplasm are not considered "real" cells, they do not have a cell nucleus, ribosomes and vacuoles .

In most plants, sieve tubes function for no more than a year, but there are exceptions: they exist in grapes for 2 years, in linden for several years, while in some palm trees several dozen. At the end of the growing season, sieve perforations are completely clogged with callose, which is also deposited on both sides of the sieve plate, resulting in the formation of corpus callosum. The defective sieve tubes and surrounding cells become deformed and obliterated over time.