Apoferritin in the vacuolar system of insect hemocytes.

Electron microscopy showed no holoferritin in either the cytosol or the vacuolar system of hemocytes (granulocytes) from normal Calpodes ethlius larvae. This does not mean that ferritin is normally absent from hemocytes, since apoferritin lacks contrast and would not be observed. In vitro iron in glycerol treatment of hemocytes from normal larvae caused holoferritin cores to be visible in the rough endoplasmic reticulum, suggesting that hemocytes from normal larvae contain apoferritin. Hemocytes are therefore like the fat body, and could also be a source of hemolymph ferritin. After loading the hemolymph with iron in vivo, many holoferritin cores were resolvable in the vacuolar system of some hemocytes. Ferritin synthesis can therefore be induced by elevated hemolymph iron levels. Iron loading of epidermis and heart showed similar ferritin cores but more rarely. In all tissues they occurred in the secretory pathway and not in the cytosol.