The distribution of iron in Daphnia in connexion with the synthesis and breakdown of haemoglobin

Abstract

Experimental studies have previously been made on invertebrates with haemoglobin in the body fluids. In spite of this the site of formation and breakdown of the respiratory pigment is, in many eases unknown. The aim of this work has been to show these sites in an arthropod, which possesses haemoglobin in the blood, namely Daphnia (Crustacea, Cladocera). The haemoglobin of Daphnia is synthesised in the large fat- and glycogen-containing cells of the fat body. This is an extensive organ which lines the haemocoel and so is everywhere bathed by blood. These fat cells often contain Iron and sometimes haemoglobin. A synthesis of haemoglobin may also take place in the ovaries. A breakdown of haemoglobin occurs in the fat body where Iron is found in an unbound form when the blood haemoglobin content falls. The fate of Iron released from haemoglobin breakdown, differs in Daphnia, from that in mammals. in Daphnia iron has been found in the paired excretory organs following a loss of haemoglobin from the blood. Experimental studies and a study of the histological distribution of iron, have indicated that this iron is excreted. Mammals retain iron, as stores of ferritin, but ferritin has not been found in Daphnia. A histochemical test for bile pigments, failed to reveal any such pigments in Daphnia. Green pigments have been found in Daphnia, these are sometimes carotenoid protein complexes, sometimes green derivatives of haemoglobin, which are not bile pigments. Preliminary results have indicated that a general increase of haem compounds accompanies an increase in the haemoglobin content of the blood. The work is presented as a histochemical study. The distribution of Inorganic iron, organic iron and haem iron, has been studied and it has been found that the distribution of iron is related to the condition of the haemoglobin in the blood. Some experimental work has been undertaken to confirm histochemical observations.