In the absence of a nucleus how are the functions of a sieve tube maintained?

Explanation

i.Sieve tubes are associated with companion cells. Which are thin walled specialised parenchyma cells with a nucleus.
ii.They are living and are connected to sieve tubes. Through pits found in their lateral walls.
iii Cytoplasmic connections are maintained through pits between sieve tube and companion cell.
iv. this helps to maintain the pressure gradient in sieve tubes.
v. the nucleus of companion cells control the sieve tube.