HETEROGENEOUS DISTRIBUTION OF ELEMENTAL CONTENTS IN THE LARVAL MALPIGHIAN TUBULES OF DROSOPHILA-HYDEI - X-RAY-MICROANALYSIS OF FREEZE-DRIEDCRYOSECTIONS

The elements Na, Cl and K are distributed heterogeneously in the larva l cells of the four Malpighian tubules of Drosophila hydei. Elemental gradients are steeper when they are related to the dry weight in compa rison to the weight of water. The high contents of Na, Cl and K in the cytoplasm close to the basal plasma membrane differ significantly fro m the low values found in the neighboring basal '' labyrinth '' and in the intermediate cytoplasm. Elemental contents (K, Cl) increase from the intermediate cytoplasm to the apical microvilli and further to the lumen. The K/Na-ratio changes across the cells from 0.9 in the hemoly mph to 2 in the basal cytoplasm close to the plasma membrane, to 27 in the microvilli, and 89 in the fluid phase of the lumen. In the lumen, K is accumulated in proteoglycan containing type-II concretions. The water content increases from the distal to the proximal segments of an terior and posterior tubules.