ISSN:
1432-1351
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
,
Medizin
Notizen:
Summary The compound eye of the tobacco hornworm mothManduca sexta differentiates during the 3 to 4 week period of the pupal instar. We used a morphological system to divide pupal development into 17 stages, each stage representing from 1 to 2 days of chronological age. We followed the progressive maturation of retinular ultrastructure, measured rhodopsin in slices of retina by microspectrophotometry (MSP), and recorded electroretinograms (ERGs) from stages 8 to 17. 1. Endomembrane that accumulates within the receptor cells between stages 5 and 7 (Fig. 3) appears to contribute to the formation of rhabdomere microvilli beginning at stage 9 or 10 (Fig. 4). Rhabdomere volume increases by at least 30-fold between pupal stage 11 and the adult moth. 2. The first ERGs were recorded at stage 10 (Fig. 6, 7) when the rhabdomeres begin to differentiate. The earliest ERGs are pure receptor potentials; higher order components do not appear until stage 14–15. Photoreceptor response, determined by the light intensity required to elicit 1 mV criterion responses from dark-adapted eyes at peak ultradian or circadian sensitivity, increases by a factor of 105 between stages 11 and 15. A further 3 log unit increase between stages 15 and 16, brings it nearly to the adult level. This final jump in responsiveness results from the initial migration of distal screening pigment into its normal dark-adapted position during stage 15. 3. The retina of the adult contains three visual pigments: a green sensitive rhodopsin (R520) and smaller amounts of blue sensitive (R440) and ultraviolet sensitive (R345) rhodopsins. No rhodopsin was measured prior to pupal stage 6. R520, the easiest of the rhodopsins to measure, is first present in developing retinas at stage 6–7 (Fig. 9). We have evidence that R440 is present from at least stage 12, and R345 from at least stage 15. At stage 10, when the rhabdom is just beginning to form, the retina already contains 10–20% of the adult concentration of R520 (Fig. 11). At stage 11 and later, R520 is transformed by orange light to stable metarhodopsin (M485), which can be photoregenerated to R520 with blue light (Fig. 10). At stages 7 and 8, the metarhodopsin of R520 differs from that of the later pupal stages and the adult moth (Fig. 12). Itsλ max is about 470 nm, and photoreversal does not occur. 4. Since the retina contains rhodopsin prior to the formation of the rhabdomere microvilli, and a relatively large amount is present when the rhabdomeres are just forming, there must be an extrarhabdomeric pool of rhodopsin. During these early pupal stages, rhodopsin may be associated with the endomembranes of the differentiating photoreceptor cells.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00606365
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