Final answer:
The bluish cytoplasm of reticulocytes when stained with Wright-Giemsa is due to the presence of residual ribosomal RNA. These RNA remnants are part of the ribosome networks retained by immature erythrocytes and give the characteristic color before the cell fully matures and loses these organelle remnants.
Step-by-step explanation:
Reticulocytes, which are immature erythrocytes, have a bluish cytoplasm when stained with Wright-Giemsa stain. This bluish color is attributed to the presence of residual ribosomal RNA (rRNA) within the cell. As reticulocytes mature in the bone marrow, they extrude their nucleus and most other organelles but initially may retain some organelles like ribosomes. The reticulum or network of ribosomes, which contain ribosomal RNA, is responsible for the blue hue observed in the stain. These remnants of the ribosomes are quickly lost as the reticulocytes develop into mature erythrocytes, which then lack internal structures like nuclei, endoplasmic reticulum, and ribosomes, and primarily contain hemoglobin for oxygen transport.