ISSN:
1432-234X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary Light- and dark-adapted ocelli (LL and DD for 30 h) of seastars were studied by thin sectioning and freeze-fracture techniques for electron microscopy, and by histofluorescence. Lighting conditions affected the ultrastructure of the sensory microvilli, which became longer, more numerous, and more regularly arranged in darkness. A significant reduction in the density of intramembranous particles (IMPs) occurred in the sensory microvilli of LL specimens (6,600/µm2 in DD, 3,000/µm2 in LL) and, to a lesser extent, in the apical projections, but not in other membranous components including the cilia of the sensory cells. Additional observations on four other species revealed higher densities of IMPs in sensory microvilli than those in cilia. The fact that IMP densities of the LL sensory microvilli and the pinocytotic vesicles were nearly the same was considered to show the relationship of the two membranous structures. A specific fluorescence, indicative of the presence of retinal-based proteins, appeared only in the ocellar lumen of DD specimens, but practically none in LL ones. It was suggested that in the seastar ocelli the sensory microvilli are the primary photoreceptive sites and that they contain a rhodopsin-like substance. These conclusions support the view that asteroid photoreceptors are microvillar and not ciliary.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00310473
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