Photoreceptor membrane breakdown in the spider Dinopis: The fate of rhabdomere products

Summary Photoreceptor membrane breakdown at dawn in the posterior median eyes of the spider Dinopis is described. Coated and smooth vesicles are shed into the receptor cytoplasm and are assembled into multivesicular bodies of two kinds: (i) Coated vesicles form loosely-assembled multivesicular bodies (mvbs) whose bounding membranes are derived from endoplasmic reticulum. (ii) Smooth vesicles generated by the mass disintegration of membrane aggregate to yield tightly-assembled multivesicular bodies which are not membrane-bound. Both types are either lysed in the inter-rhabdomeral cytoplasm, or degrade via multi-lamellar bodies to residual bodies (rbs) while they are being transported to the intermediate segments. Two systems are associated with lysis. Nebenkerne produced by the rapid differentiation of GERL in the intermediate segments fuse with membrane-bound mvbs or rbs and may inject them with hydrolases. Partially-differentiated rigid tubules (Blest et al., 1978) travel to the receptive segments together with RER from the intermediate segments and also fuse with or engulf mvbs. Both systems may contain pro-enzymes which are activated at their target sites. No evidence of a close or necessary geometrical relationship between GERL and Golgi bodies has been seen, and there is no clear demarcation between RER, smooth ER and GERL which is entering into continuity with or engulfing mvbs. The implications of these findings for hypotheses about the origins of isolation membranes and autolytic systems in invertebrate systems are briefly discussed.The authors thank Professor D.T. Anderson, F.R.S., for our use of field facilities at the Crommelin Biological Field Station of Sydney University at Warrah, Pearl Beach, N.S.W., Andrew & Sally Austin and Sally Stowe for help in the field, and Joanne Maples for technical assistance. Professor T.H. Waterman and Dr. V.B. Meyer-Rochow kindly gave us access to certain of their results prior to publication. We are indebted to Rod Whitty and the Electron Microscopy Unit for advice and support throughout these studies