Nocturnal rhabdom cycling and retinal hemocyte functions in crayfish (Procambarus) compound eyes. I. Light microscopy

Abstract

AbstractIn addition to the previously known photoreceptor membrane cycle coupled to light and dark adaptation, detailed study of the late‐night period (24:00 to 06:00 h) in Procambarus compound eyes demonstrates that a second cycle of degradation (about 14% decrease in maximum rhabdom diameter) and resynthesis takes place completely in the dark between midnight and dawn.Invasive granular hemocytes are present in the retina throughout the latenight period in winter. Their distribution around the retinulas during the degradative phase (24:00 to 02:00 h) of the turnover cycle differs significantly from that characteristic of both the synthetic (02:00 to 04:00 h) and resting (04:00 to 06:00 h) phases. This correlation provides an important way of identifying retinal areas in the process of net photoreceptor membrane degradation. Retinal hemocytes are highly significantly more numerous in the resting stage than in either of the other two.Certain associated changes differ between winter and summer series. Total hemocyte numbers in our winter experiments show a positive linear correlation with rhabdom diameters. In the summer series, retinal hemocytes are rare or absent, and rhabdom diameters are significantly smaller than in winter. No hemocytes are associated with the smallest (June) rhabdoms. Yet the latter do show the late‐night breakdown and regeneration. Correlation between hemocyte numbers and rhabdom size becomes almost perfect if our summer and winter series are pooled.