Cytochemical localization of acid phosphatase in ocelli of the seastar Patiria miniata during recycling of photoreceptoral membranes

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Abstract
The amount and distribution of the lysosomal enzyme acid phosphatase in ocelli of seastars (Patiria miniata) in a 24‐hour light‐dark cycle were studied by a standard cytochemical technique. The enzyme was found in the Golgi apparatus, GERL, and primary and secondary lysosomes of sensory and pigmented supportive cells. We conclude that photoreceptoral membrane of the sensory microvilli is resorbed inthe day by incorporation into pinocytotic vesicles and saccules and degraded in the late day and at night in the secondary lysosomes. Photoreceptoral membrane of microvilli abscised into the ocellar cavity in the day is probably recycled by phagocytosis and digestion in secondary lysosomes of the supportive cells, and perhaps to a lesser extent in the corneal cells. We speculate that recaptured molecules, including photopigment, are returned, in some unknown way, to the distal ends of the sensory cells where the receptoral microvilli are regenerated in the dark. Pinocytotic vesicles may provide stored membrane.