Summary
Pea aphid primary symbiotes have previously been shown to synthesize cholesterol in vitro. Two electron microscopic techniques were used here to determine whether the symbiotes also synthesize cholesterol in vivo and whether this cholesterol is made available to the aphid. We also inquired into a possible role of secondary symbiotes in cholesterol biosynthesis. Treatment of aphids with digitonin resulted in significant alteration of ultrastructural sites in primary and secondary symbiote membranes. We concluded that these sites are areas of high cholesterol concentration in the symbiotes.
Electron microscopic autoradiography with 3H-mevalonate precursor indicated that both primary and secondary symbiotes synthesize cholesterol; in both cases, the majority of grains were associated with the symbiote membranes. While the frequency of grains on the symbiotes remained constant, irrespective of incubation time in labelled media, the frequency of grains over surrounding tissues increased exponentially as the time of incubation was increased from 30 min to 8 h, indicating that symbiote cholesterol is transported to other tissues. High voltage electron microscopic autoradiography permitted thick section autoradiography, reducing the time of emulsion exposure from 54 days (thin section) to 12 days (0.5 μm sections).
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Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, and by a research grant (PCM 74-2401 A01) from The National Science Foundation
The authors wish to thank Dr. G.A. DeZoeten for his invaluable advice and assistance with the autoradiographic techniques, Mr. Gary Gaard for his help with electron microscopy, and Dr. Dale Johnston and Dr. Damien Neuberger for their generous help in the use of the high voltage EM
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Griffiths, G.W., Beck, S.D. In vivo sterol biosynthesis by pea aphid symbiotes as determined by digitonin and electron microscopic autoradiography. Cell Tissue Res. 176, 179–190 (1977). https://doi.org/10.1007/BF00229461
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DOI: https://doi.org/10.1007/BF00229461