What is the main difference between mature xylem cells and mature ploloem cells?

Both xylem and phloem are vascular tissues. Xylem is a tubular structure which is responsible for water transport from the roots towards all of the parts of the plant. Phloem is also a tubular structure but is responsible for the transportation of food and other nutrients needed by plant. Xylem exists as non-living tissue at maturity, but phloem is living cells.

Xylem cells die as they mature while phloem cells are alive at maturity.