I know that sieve tubes do not have ribosomes, nuclei and cytoskeletal elements. What other organelles does it not have? Does it have a cytoplasm?
The sieve tubes of the phloem in angiosperms consist of sieve tube elements or members. These are cells which lose their nucleus, ribosomes, and vacuoles at maturity. They of course have cytoplasm, and it is connected by channels to companion cells (which do have these organelles). The sieve tube elements retain mitochondria and plastids. See the Wikipedia page and this page for more details.