Ageing adipokinetic cells in Locusta migratoria: an ultrastructural morphometric study

A morphometric study was made of the ultrastructure of adipokinetic cells in resting adults of Locusta migratoria at 3, 23, and 43 days after imaginal ecdysis. The nucleus, rough endoplasmic reticulum, and Golgi apparatus enlarge with age, which indicates that the synthesis and packaging of secretory substances increases during ageing. The size of the storage compartment, consisting of secretory and ergastoplasmic granules, does not increase earlier than 23-43 days after imaginal ecdysis. The lysosomal compartment markedly enlarges between 3 and 23 days; later on, the growth of this compartment, especially of autophagosomes, is less prominent. This suggests that lysosomal destruction initially compensates for the production of new secretory granules, assuming that exocytosis of secretory granules by adipokinetic cells is insignificant in resting locusts. Afterwards, lysosomal destruction may no longer be sufficient to prevent over-production of secretory granules, as is suggested by the increase in the number of these granules between 23 and 43 days. This coincides with the appearance of a considerable number of large ergastoplasmic granules, which represent a spatially more efficient form of storage of secretory material than the much smaller secretory granules. The increase with age in the amount of secretory products indicates that the biosynthetic activity of the adipokinetic cells is not (finely) tuned to their releasing activity.