ACTIN-DEPENDENT LIGHT-INDUCED TRANSLOCATION OF MITOCHONDRIA AND ER CISTERNAE IN THE PHOTORECEPTOR CELLS OF THE LOCUST SCHISTOCERCA-GREGARIA

Light-dependent changes in the positioning of organelles in photorecep tor cells of arthropods are a well-known phenomenon. In this study, we examine the role of the cytoskeleton in these light-dependent antagon istic movements. In dark-adapted photoreceptor cells of the locust Sch istocerca gregaria, prominent sacs of smooth endoplasmic reticulum (ER ) oppose the bases of the photoreceptive microvilli. Light stimulation causes a translocation of the ER elements towards the main cell body, and an aggregation of mitochondria adjacent to the microvilli. Immuno fluorescence studies and electron-microscopic examination of chemicall y fixed or high-pressure-frozen, freeze-substituted specimens demonstr ate a lack of microtubules in the submicrovillar region. However, nume rous filament bundles are aligned in close association with mitochondr ia and ER elements, along the track of their movement. Fluorescent pha llotoxins and monoclonal antiactin antibodies label filament bundles i n the submicrovillar region, indicating that they are composed of F-ac tin. Finally, depolymerization of the submicrovillar actin filaments b y incubation with cytochalasin B results in a blockade of the movement of mitochondria and ER cisternae towards the rhabdom. These results s uggest that the light-dependent translocation of both ER cisternae and mitochondria occurs along actin filaments.