Mature sieve tube elements retain a highly developed rough endoplasmic reticulum and ribosomes to synthesise the proteins required for active translocation.

Lignified cell walls in mature xylem vessel elements prevent the tubes from collapsing inward under the tension created by the transpiration pull.

Active loading of sucrose involves the active transport of hydrogen ions ($H^{+}$) into companion cells from the apoplast, establishing a proton gradient that drives sucrose symport.

Sieve plates are highly lignified end-walls that contain sieve pores, which actively pump sucrose solution from one sieve tube element to the next.