Autoradiography of Photomembrane in HEMIGRAPSUS NUDUS
Protein synthesis was studied in the visual cells of Hemigrapsus nudus by light microscope autoradiography. Two hours before sunset, crabs were injected with a single dose of tritiated leucine and sacrificed at time intervals coincident with dynamic retinal changes observed in electron microscope (EM) studies of related Arthropods (Blest, 1978 and Stowe, 1980). Two separate experiments were performed to examine time periods in the renewal process. Some periods in each experiment were overlapped to develop more accurate decay curves. Experiment I followed time regimes of 0.5, 1.5, 2.5, 3.0, 3.0, 5.0, and 6.0 hours after sunset. Autoradiographs of retinula cells were examined for temporal variations in grain concentration and in spatial distribution patterns. The concentration of leucine in the retinula cells peaked at 1.5 hours, declined until the third hour, and leveled off through hour six. Region II peripheral to the rhabdome showed the highest concentration for all sample times. In Experiment II, greater resolution of peak times for grain concentration was obtained using sacrifice regimes of 0.0, 0.5, 1.0, 1.5, and 2.5 hours after sunset. Also evaluated were temporal variations in rhabdomeral-cystoplasmic distribution. Other retinula cells were sampled at 0.5 and 1.0 hours after injection to determine the path of newly-synthesized protein before induction of the dark phase. Finally, similar evaluations of grain count and distribution were performed on autoradiographs of visual cells at sunrise (sample times: 0.0, 1.0, 2.0 hours after sunrise) and after long-term exposure to tritiated leucine (sample times: 1, 2, and 7 days after injection, maintaining normal 12:12 Light:Dark conditions). Results from Experiment II showed a peak time for grain concentration to be closer to 1.0 hour after sunset rather than the 1.5 hours of Experiment I. Spatially, labeled protein was more concentrated within the cytoplasm until 0.5 hour after sunset, when the higher proportion of grains shifted to the rnicrovilli, the area specialized for light absorption. Long-term samples continued to show the same spatial differentiation while declining in overall count.
Physiology, Crabs -- physiology; Crustacea -- physiology; Proteins -- metabolism; Retina
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